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Archive for the ‘Oxidative phosphorylation’ Category

Studies of Respiration Lead to Acetyl CoA

Curator: Larry H. Bernstein, MD, FCAP

In this series of discussions it has become clear that the studies of carbohydrate metabolism were highlighted by Meyerhof’s work on the glycolytic pathway, and the further elucidation of a tie between Warburg’s studies of impaired respiration for malignant aerobic cells relying on glycolysis, comparanle to Pasteur’s observations 60 years earlier by for yeast.   The mitochondrion was unknown at the time, and it took many years to discover the key role played by oxidative phosphorylation and Fritz Lipmann’s discovery of “acetyl coenzyme A, and the later explanation of electron transport.  This was crucial to understanding cellular energetics, which explains the high energy of fatty acid catabolism from stored adipose tissue.  I shall here embark on a journey to trace these important connected developments.

  1. Signaling and signaling pathways
  2. Signaling transduction tutorial.
  3. Carbohydrate metabolism

3.1  Selected References to Signaling and Metabolic Pathways in Leaders in Pharmaceutical Intelligence

  1. Lipid metabolism

4.1  Studies of respiration lead to Acetyl CoA

  1. Protein synthesis and degradation
  2. Subcellular structure
  3. Impairments in pathological states: endocrine disorders; stress hypermetabolism; cancer.

Phosphorylation

In some reactions, the purpose of phosphorylation is to “activate” or “volatize” a molecule, increasing its energy so it is able to participate in a subsequent reaction with a negative free-energy change. All kinases require a divalent metal ion such as Mg2+ or Mn2+ to be present, which stabilizes the high-energy bonds of the donor molecule (usually ATP or ATP derivative) and allows phosphorylation to occur.This is a major focus of this discussion.

In other reactions, phosphorylation of a protein substrate can inhibit its activity (as when AKT phosphorylates the enzyme GSK-3). When src is phosphorylated on a particular tyrosine, it folds on itself, and thus masks its own kinase domain, and is thus turned “off”. In still other reactions, phosphorylation of a protein causes it to be bound to other proteins which have “recognition domains” for a phosphorylated tyrosine, serine, or threonine motif. In the late 1990s it was recognized that phosphorylation of some proteins causes them to be degraded by the ATP-dependent ubiquitin/proteasome pathway. This is all that needs to be said at this time about proteins.

 

Oxidative Phosphorylation

ATP is the molecule that supplies energy to metabolism. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is probably so pervasive because it is a highly efficient way of releasing energy, compared to alternative fermentation processes such as anaerobic glycolysis.

During oxidative phosphorylation, electrons are transferred from electron donors to electron acceptors such as oxygen, in redox reactions. These redox reactions release energy, which is used to form ATP. In eukaryotes, these redox reactions are carried out by a series of protein complexes within the cell’s intermembrane wall mitochondria, whereas, in prokaryotes, these proteins are located in the cells’ intermembrane space.

O t to  W a r b u r g
Nobel Lecture, December 10, 1931

The oxygen-transferring ferment of respiration

The effects of iron are very great, and it follows that oxidation and reduction of the ferment iron must occur extremely rapidly. In fact, almost every molecule of oxygen that comes into contact with an atom of ferment iron reacts with it.  Complex-bound bivalent iron in compounds reacts, in vitro as well as in the cell, with molecular oxygen. tt is not yet possible to reduce in vitro trivalent iron with the cell fuel: it is always necessary to add a substance of unknown composition, a ferment, that activates the combustible material for the attack of the iron. It must, therefore, be concluded that activation of the combustible substance in the breathing cell precedes the attack of the ferment iron; this corresponds with “hydrogen activation” as postulated in the theory of Wieland and Thunberg. According to the results of a joint research with W. Christian, this is a cleavage comparable with those known as fermentation.

It is possible that the interplay of splitting ferment and oxygen-transferring ferment does not fully explain the mechanism of cellular respiration; that the iron that reacts with the molecular oxygen does not directly oxidize the activated combustible substances, but that it exerts its effects indirectly through still other iron compounds – the three non-auto-oxidizable cell hemes of MacMunn, which occur in living cells according to the spectroscopic observations of MacMunn and Keilin, and which are reduced in the cell under exclusion of oxygen. It is still not possible to answer the question whether the MacMunn hemes form part of the normal respiratory cycle, i.e., whether respiration is not a simple iron catalysis but a four-fold one. The available spectroscopic observations are also consistent with the view that the MacMunn hemes in the cell are only reduced when the concentration of activated combustible substance is physiologically above normal. This will suffice to indicate that oxygen transfer by the iron of the oxygen transferring ferment is not the whole story of respiration. Respiration requires not only oxygen-transferring ferment and combustible substance, but oxygen-transferring ferment and the living cell.

Inhibition of cellular respiration by prussic acid was discovered some 50 years ago by Claude Bernard, and has interested both chemists and biologists ever since. It takes place as the result of a reaction between the prussic acid and the oxygen-transferring ferment iron, that is, with the ferment iron in trivalent form. [In the prussic acid reaction] the oxidizing OH-group of the trivalent ferment-iron is replaced by the non-oxidizing CN-group, thus bringing transfer of oxygen to a standstill. Prussic acid inhibits reduction of the ferment iron. Inhibition of respiration by carbon monoxide was discovered only a few years ago. [Given] the initial reaction in respiration, then, in the presence of carbon monoxide, the competing reaction will also occur and, varying with the pressures of the carbon monoxide and of the oxygen, more or less of the ferment iron will be removed from the catalytic process on account of fixation of carbon monoxide to the ferment iron. Unlike prussic acid, therefore, carbon monoxide affects the bivalent iron of the ferment. Carbon monoxide inhibits oxidation of the ferment iron.

Thus inhibition of respiration by carbon monoxide, unlike that by prussic acid, depends upon the partial pressure of oxygen. The toxic action of prussic acid in the human subject is based on its inhibitory action on cellular respiration. The toxic effect of carbon monoxide on man has nothing to do with inhibition of cellular respiration by carbon monoxide but is based on the reaction of carbon monoxide with blood iron. For, the effect of carbon monoxide on blood iron occurs at pressures of carbon monoxide far from the level at which cellular respiration would be inhibited.

If carbon monoxide is added to the oxygen in which living cells breathe, respiration ceases, as has already been mentioned, but if exposure to ultraviolet or visible light is administered, respiration recurs. By alternate illumination and darkness it is possible to cause respiration and cessation of respiration in living, breathing cells in mixtures of carbon monoxide and oxygen. In the dark, the iron of the oxygen-transferring ferment becomes bound to carbon monoxide, whereas in the light the carbon monoxide is split off from the iron which is, thus, liberated for oxygen transfer. This fact was discovered in 1926 in collaboration with Fritz Kubowitz. Photochemical dissociation of iron carbonyl compounds was discovered in 1891 by Mond and Langer, by exposing iron pentacarbonyl. This reaction is specific for carbonyl compounds of iron, most of which appear to dissociate in the presence of light, e.g., carbon-monoxide hemoglobin (John Haldane, 1897) carbon-monoxide hemochromogen (Anson and Mirsky, 1925), carbon-monoxide pyridine hemochromogen (H. A. Krebs, 1928), and carbon-monoxide ferrocysteine (W. Cremer, 1929).

When the photochemical dissociation of iron carbonyl compounds is measured quantitatively (we followed hereby Emil Warburg’s photochemical experiments), by using monochromatic light and comparing the amount of light energy absorbed with the amount of carbon monoxide set free, it is found that Einstein’s law of photochemical equivalence is very exactly fulfilled. The number of FeCO-groups set free is equal to the number of light quanta absorbed, and this is independent of the wavelength employed.

Photochemical dissociation of iron carbonyl compounds can be used to determine the absorption spectrum of a catalytic oxygen-transferring iron compound. One combines the catalyst in the dark with carbon monoxide, and so abolishes the oxygen-transferring power of the iron. If then this is exposed to monochromatic light of various wavelengths and of measured quantum intensity, and the effect of light W measured the increase in the rate of catalysis – it is found that the effects of the light are proportional to the quanta absorbed. The arrangement becomes very simple if the catalyst is present, as is usually the case, in infinitesimally low concentration in the exposed system. Then the thickness of the layers related to the amount of absorption of light can be considered to be infinitely thin, the number of quanta absorbed is proportional to the number of quanta supplied by irradiation.

In collaboration with Erwin Negelein, this principle was employed to measure the relative absorption spectrum of the oxygen-transferring respiratory ferment. The respiration of living cells was inhibited by carbon monoxide which was mixed with the oxygen. We then irradiated with monochromatic light of various wavelengths and of measured quantum intensity, and [measured] the increase of respiration together with the relative absorption spectrum. Only practically colorless cells are suitable for this type of experiment, [which requires] a layer infinitely thin with regard to light absorption.

Imagine living cells whose respiration is inhibited by carbon monoxide. If these are irradiated, respiration does not increase suddenly from the dark to the light-value, but there is a definite, although very short, interval until the combination of carbon monoxide with the ferment is broken down by the light. Even without calculation, it is obvious that the rate of increase in the effect of light must be related to the depth of colour of the ferment. If the ferment absorbs strongly, the -monoxide compound will be rapidly broken down, and vice versa.

The time of increase of the action of light can be measured. The time taken for a given intensity of light to cause dissociation of approximately half the carbon-monoxide compound of the ferment can be measured and, from this time, and from the effective intensity of light, the absolute absorption coefficient of the ferment for every wavelength can be calculated. The absorption capacity of the ferment, measured in accordance with this principle, was found to be of the same order as the power of light absorption of our strongest pigments. If one imagines a ferment solution of molar concentration, a layer of 2 x 10-6 cm thickness would weaken the blue mercury line 436 µµ up by half. The fact that the ferment in spite of this cannot be seen in the cells is due to its low concentration.

Monochromators and color filters were used to isolate the lines from these sources of light. If the absorption coefficient is entered as a function of the wavelength, the absorption spectrum of the carbon-monoxide compound of the ferment is obtained. The principal absorption-band or y-band lies in the blue.
This is the spectrum of a heme compound, according to the position of the bands, the intensity state of the bands, and the absolute magnitude of the absorption coefficients.

It appeared essential to have a control to ascertain whether heme as an oxidation catalyst of carbon monoxide and prussic acid really behaves like the ferment. If cysteine is dissolved in water containing pyridine, and a trace of heme is added, and this is shaken with air, the cysteine is catalytically oxidized by the oxygen-transferring power of the heme. According to Krebs, the catalysis is inhibited by carbon monoxide in the dark, but the inhibition ceases when the mixture is illuminated. Prussic acid too acts on this model on cellular respiration, inasmuch as it combines with the trivalent heme and inhibits its reduction. Just as in life, inhibition by carbon monoxide is dependent on the oxygen pressure, while inhibition by prussic acid is independent of the oxygen pressure.

In conjunction with Negelein, this model was also used to test the ferment experiments quantitatively. Heme catalysis in the model was inhibited by carbon monoxide in the dark. Then monochromatic light of known quantum intensity was used to irradiate it, and the absorption spectrum of the catalyst calculated from the effect of the light which was known from direct measurements on the pure substance. The calculation gave the absorption spectrum of the heme that had been added as a catalyst, and so the method was verified as a technique for the determination of the ferment spectrum, both the calculation and the measurement method.

The positions of the principal band and a-band of the ferment are:

Principal band            α-band

433 µµ                    590 µµ

These will be referred to as the “ferment bands” because the ferment was the first for which they were determined. Hemes are the complex iron compounds of the porphyrins, in which two valencies of the iron are bound to nitrogen. The porphyrins, of which Hans Fischer determined the chemical structure, are tetrapyrrole compounds in which the four pyrrole nuclei are held together by four interposed methane groups in the cr-position. Green, red, and mixed shades of hemes are known. If magnesium is replaced by iron in chlorophyll, green hemes are obtained. Their color is due to a strong band in the red which is already recognized in chlorophyll. The ferment does not absorb in the red and cannot, therefore, be a green heme. Red hemes are the usual hemes in blood pigment and in its related substances, such as mesoheme and deuteroheme. Coproheme is also a red heme which is an iron compound of the coproporphyrin that H. Fischer recognized in the body. Other red hemes are 20 µµ further from the red than the ferment bands. It follows that the ferment is not a red heme.

The pheoporphyrins are closely related to blood pigment but, as H. Fischer showed, pheoporphyrin a is simply mesoporphyrin in which the one propionic acid has been oxidized so that ring closure with the porphyrin nucleus is made possible. Pheoporphyrin a is a reduction product of chlorophyll a or an oxidation product of blood pigment, and connects together, in an amazingly simple manner, the principal pigments of the organic world the blood pigment and the leaf pigment.

Chlorophyll b has, in general, bands of longer wavelength than chlorophyll a, and for this reason,

  1. Christian and I applied Fischer’s reduction method to it. In this way we obtained pheoheme b, which, when linked with protein, corresponds with the ferment in respect to the position of the principal band. The principal band of the carbon-monoxide compound of pheohemoglobin b is 435 µµ.
  2. However, while the principal band of pheohemoglobin corresponds with the ferment bands within the permitted limits, the α-band shifts so far beyond them because it lies too near the red. It is, nevertheless, interesting that
  3. when ‘chlorophyll b is reduced, one obtains a pheoporphyrin of which the heme of all the pheohemes that have been demonstrated up to the present time is the most like the ferment.

 

Still nearer the ferment in its spectrum, is a heme occurring in Nature. This is

  • spirographis heme, which has been isolated from chlorocruorin, the blood pigment of the bristle-worm Spirographis,

in collaboration with Negelein and Haas, the bands of spirographis heme, coupled to globin, are :

  • carbon-monoxyhemoglobin of spirographis:  principle band, 434 µµ; α-band, 594 µµ.

Spirographis heme differs from the red hemes by the surplus or ketone oxygen-atom, and is classified as pheoheme. Like Fischer’s pheohemes, spirographis heme is intermediate between chlorophyll and blood pigment in respect of

  • the degree of oxidation of the side-chains.

The two hemes with a spectrum most like that of the ferment – pheoheme b and spirographis heme – possess a remarkable property. If they are dissolved in dilute sodium-hydroxide solution, in the form of ferrous compounds,

  • the absorption bands slowly wander towards the blue, near the bands of blood heme. In this way,
  • mixed-color hemes have been converted into red hemes.

On acidification, the change reverts: the <<blood bands>> disappear and

  • the ferment bands appear.

This experiment shows that

  1. oxidation of the side-chains does not suffice to give rise to the ferment bands, but
  2. some process of the type of anhydride formation must also occur.

The unique intermediate status of the ferment-like hemes demonstrated by these simple experiments suggests

  1. the suspicion that blood pigment and leaf pigments have both arisen from the ferment –
  2. blood pigments by reduction, and leaf pigment by oxidation.
  • For evidently, the ferment existed earlier than hemoglobin and chlorophyll.

The investigations on the oxygen-transferring ferment have been supported from the start by the Notgemeinschaft der deutschen Wissenschaft and the Rockefeller Foundation, without whose help they could not have been carried out. I have to thank both organizations here.

A L B E R T S Z E N T- GY Ö R G Y I      Nobel Lecture, December 11, 1937

Oxidation, energy transfer, and vitamins

A living cell requires energy not only for all its functions, but also

  • for the maintenance of its structure.
  • The source of this energy is the sun’s radiation.

Energy from the sun’s rays is trapped by green plants, and

  • converted into a bound form, invested in a chemical reaction.

When sunlight falls on green-plants, they liberate oxygen from carbon dioxide, and

  1. store up carbon, bound to the elements of water, as carbohydrate.

The radiant energy is now locked up in this carbohydrate molecule. This molecule is our food. When energy is required,

  • the carbohydrate is again combined with oxygen to form carbon dioxide, oxidized, and energy released.

Investigations during the last few decades have brought hydrogen instead of carbon, and instead of CO2 water, the mother of all life, into the foreground. It is becoming increasingly probable that

  1. radiant energy is used primarily to break water down into its elements,
  2. while CO2, serves only to fix the elusive hydrogen thus released.

While this concept of energy fixation was still being developed, the importance of hydrogen in the reversal of this process, whereby energy is liberated by oxidation, had already been confirmed by H. Wieland’s experiments.

Our body really only knowns one fuel, hydrogen. The foodstuff, carbohydrate, is essentially a packet of hydrogen, a hydrogen supplier, a hydrogen donor, and the main event during its combustion is

  • the splitting off of hydrogen.

So the combustion of hydrogen is

  • the real energy-supplying reaction;

To the elucidation of reaction (6), which seems so simple, I have devoted all my energy for the last fifteen years.

When I first ventured into this territory, the foundations had already been laid by the two pioneers H. Wieland and
O. Warburg, and Wieland’s teaching had been applied by Th. Thunberg to the realm of animal physiology.Wieland and Thunberg showed, with regard to foodstuffs, how

  1. the first step in oxidation is the “activation” of hydrogen, whereby
  2. the bonds linking it to the food molecule are loosened, and
  3. hydrogen prepared for splitting off.

But at the same time oxygen is also, as Warburg showed,

  • activated for the reaction by an enzyme.
  • the hydrogen-activating enzymes are called dehydrases or dehydrogenases.

Warburg called his oxygen-activating catalyst, “respiratory enzyme”.These concepts of Wieland and Warburg were apparently contradictory, and

  1. my first task was to show that the two processes are complementary to one another, and that
  2. in muscle cells activated oxygen oxidizes activated hydrogen.

This picture was enriched by the English worker D. Keilin, who showed that

  • activated oxygen does not oxidize activated hydrogen directly, but
  • that a dye, cytochrome, is interposed between them.

In keeping with this function, the “respiratory enzyme” is now also called “cytochrome oxidase”.

About ten years ago, when I tried to construct this system of respiration artificially and added together the respiratory enzyme with cytochrome and some foodstuff together with its dehydrogenase, I could justifiably expect that this system would use up oxygen and oxidize the food. But the system remained inactive. I found that

  • the dehydrogenation of certain donors is linked to the presence of a co-enzyme.

Analysis of this co-enzyme showed it to be a nucleotide, identical with v. Euler’s co-zymase, which H. v. Euler and R. Nilsson had already shown to accelerate the process of dehydration. As a result of Warburg’s investigations,this co-dehydrogenase has recently come very much into the foreground. Warburg showed that

  • it contains a pyridine base, and that it accepts hydrogen directly
    [pyridine nucleotide, triphosphopyridine nucleotide, TPN]

from food when the latter is dehydrogenated. It is therefore, the primary H-acceptor.

While working on the isolation of the co-enzyme with Banga, I found a remarkable dye, which showed clearly by its reversible oxidation that it, too, played a part in the respiration. We called this new dye cytoflav. Later Warburg showed that

  • this substance exercised its function in combination with a protein.

He called this protein complex of the dye, “yellow enzyme”. R. Kuhn, to whom we owe the structural analysis of the dye, called the dye lactoflavin and, with Györgyi and Wagner-Jauregg, showed it to be identical with vitamin B,.But the respiratory system stayed inactive even

  • after the addition of both these new components, codehydrogenase and yellow enzyme.

The C4-dicarboxylic acids and their activators which Thunberg discovered are

  • interposed between cytochrome and the activation of hydrogen as intermediate hydrogen-carriers.

In the case of carbohydrate, hydrogen from the food is first taken up by oxaloacetic acid, which

  • is reacted with the cytoplasmic malic dehydrogenase (and pyridine nucleotide –
    reduced DPN[H])
    , and thereby activated.

By taking up two hydrogen atoms, oxaloacetic acid is changed into malic acid.

  • OAA + NADH – (MDH) – malate + NAD+ + H+

This malic acid now passes on the H-atoms, and thus reverts to oxaloacetic acid,

  • which can again take up new H-atoms.

Malate + NAD+ + H+ — MDH – OAA + NADH

The H-atoms released by malic acid are taken up by fumaric acid, which is similarly

  • activated by the so-called succinic dehydrogenase.

The uptake of two H-atoms

  • converts the fumarate to succinate, to succinic acid.

The two H-atoms of succinic acid are then

  • oxidized away by the cytochrome.

Finally the cytochrome is oxidized by the respiratory enzyme, and

  • the respiratory enzyme by oxygen.

The function of the C4-dicarboxylic acids is not to be pictured as consisting of a certain amount of C4-dicarboxylic acid in the cell which is alternately oxidized and reduced. Fig. 2 corresponds more to the real situation. The protoplasmic surface, which is represented by the semi-circle, has single molecules of oxaloacetate and fumarate attached to it as prosthetic groups. These fused, activated dicarboxylic molecules then temporarily bind the hydrogen from the food. The co-dehydrogenases and the yellow enzymes also take part in this system. I have attempted to add them in at the right place.

This diagram, which will probably still undergo many more modifications, states that the “foodstuff” – H-donor – starts by

  1. passing its hydrogen, which has been activated by dehydrase, to the co-dehydrogenase.
  2. The coenzyme passes it to the oxaloacetic acid*.
  3. The malic acid then passes it on again to a co-enzyme,
  4. which passes the hydrogen to the yellow enzyme.
  5. The yellow enzyme passes the hydrogen to the fumarate.
  6. The succinate so produced is then oxidized by cytochrome,
  7. the cytochrome by respiratory enzyme,
  8. the respiratory enzyme by oxygen.

So the reaction 2H + O – H2O, which seems such a simple one,

  • breaks down into a long series of separate reactions.

With each new step, with each transfer between substances,

  • the hydrogen loses some of its energy,
  • finally combining with oxygen in its lowest-energy compound.

So each hydrogen atom is gradually oxidized in a long series of reactions, and

  • its energy released in stages.

This oxidation of hydrogen in stages seems to be one of the basic principles of biological oxidation. The reason for it is probably mainly that

  • the cell would not be able to harness and transfer to other processes
  • the large amount of energy which would be released by direct oxidation.

The cell needs small change if it is to be able to

  • pay for its functions without losing too much in the process.

So it oxidizes the H-atom by stages, converting the large banknote into small change.

About half of all plants – contain a polyphenol, generally a pyrocatechol derivative, together with an enzyme, polyphenoloxidase, which oxidizes polyphenol with the help of oxygen. The current interpretation of the mode of action of this oxidase was a confused one. I succeeded in showing that the situation was simply this, that

the oxidase oxidizes the polyphenol to quinone with oxygen.

  • In the intact plant the quinone is reduced back again
  • with hydrogen made available from the foodstuff.

Phenol therefore acts as a hydrogen-carrier between oxygen and the H-donor, and we are here again faced with a probably still imperfectly understood system for

  • the stepwise combustion of hydrogen.

——————————————————————————————————————————–

Vitamin C

If benzidine is added to a peroxide in the presence of peroxidase, a deep-blue color appears immediately, which is caused by the oxidation of the benzidine. This reaction does not occur without peroxidase. I simply used some juice which had been squeezed from these plants instead of a purified peroxidase, and added benzidine and peroxide, and the blue pigment appeared, after a small delay of about a second. Analysis of this delay showed that it was due to the presence of a powerful reducing substance, which reduced the oxidized benzidine again, until it had itself been used up. Thanks to the invitation from F. G. Hopkins and the help of the Rockefeller Foundation, I was able ten years ago to transfer my workshop to Cambridge, where for the first time I was able to pay more serious attention to chemistry. Soon I succeeded in isolating the substance in question from adrenals and various plants, and in showing that it corresponded to the formula C6H8O6 and was related to the carbohydrates. This last circumstance induced me to apply to Prof. W. N. Haworth, who immediately recognized the chemical interest of the substance and asked me for a larger quantity to permit analysis of its structure.

The Mayo Foundation and Prof. Kendall came to my help on a large scale, and made it possible for me to work, regardless of expense, on the material from large American slaughter-houses. The result of a year’s

work-was 25 g of a crystalline substance, which was given the name “hexuronic acid”. I shared this amount of the substance with Prof. Haworth. He undertook to investigate the exact structural formula of the substance. I used the other half of my preparation to gain a deeper understanding of the substance’s function. The substance could not replace the adrenals, but caused the disappearance of pigmentation in patients with Addison’s disease.

In 1930 I settled down in my own country at the University of Szeged. I also received a first-rate young American collaborator, J. L. Svirbely, who had experience in vitamin research, but besides this experience brought only the conviction that my hexuronic acid was not identical with vitamin C. In the autumn of 1931 our first experiments were completed, and showed unmistakably that hexuronic acid was power- fully anti-scorbutic, and that the anti-scorbutic acitvity of plant juices corresponded to their hexuronic acid content. We did not publish our results till the following year after repeating our experiments. At this time Tillmans was already directing attention to the connection between the reducing strength and the vitamin activity of plant juices. At the same time King and Waugh also reported crystals obtained from lemon juice, which were active anti-scorbutically and resembled our hexuronic acid.

My town, Szeged, is the centre of the Hungarian paprika industry. Since this fruit travels badly, I had not had the chance of trying it earlier. The sight of this healthy fruit inspired me one evening with a last hope, and that same night investigation revealed that this fruit represented an unbelievably rich source of hexuronic acid, which, with Haworth, I re-baptized ascorbic acid. I also had the privilege of providing my two prize-winning colleagues P. Karrer and W. N. Haworth with abundant material, and making its structural analysis possible for them. I myself produced with Varga the mono-acetone derivative of ascorbic acid, which forms magnificent crystals; from which, after repeated dissolving and recrystallization, ascorbic acid can be separated again with undiminished activity. This was the first proof that ascorbic acid was identical with vitamin C.
————————————————————————————————————————————-

Returning to the processes of oxidation, I now tried to analyse further the system of respiration in plants, in which ascorbic acid and peroxidase played an important part. I had already found in Rochester that the peroxidase plants contain an enzyme which reversibly oxidizes ascorbic acid with two valencies in the presence of oxygen. Further analysis showed that here again a system of respiration was in question, in which hydrogen was oxidized by stages. I would like, in the interests of brevity, to summarize the end result of these experiments, which I carried out with St. Huszák. Ascorbic acid oxidase oxidizes the acid with oxygen to reversible dehydroascorbic acid, whereby the oxygen unites with the two labile H-atoms from the acid to form hydrogen peroxide. This peroxide reacts with peroxidase and oxidizes a second molecule of ascorbic acid. Both these molecules of dehydro-ascorbic acid again take up hydrogen from the foodstuff, possibly by means of SH-groups. But peroxidase does not oxidize ascorbic acid directly. Another substance is interposed between the two, which belongs to the large group of yellow, water-soluble phenol-benzol-r-pyran plant dyes (flavone, flavonol, flavanone). Here the peroxidase oxidizes the phenol group to the quinone, which then oxidizes the ascorbic acid directly, taking up both its H-atoms.

At the time that I had just detected the rich vitamin content of the paprika, I was asked by a colleague of mine for pure vitamin C. This colleague himself suffered from a serious haemorrhagic diathesis. Since I still did not have enough of this crystalline substance at my disposal then, I sent him paprikas. My colleague was cured. But later we tried in vain to obtain the same therapeutic effect with pure vitamin C. Guided by my earlier studies into the peroxidase system, I investigated with my friend St. Rusznyák and his collaborators Armentano and Bentsáth the effect of the other link in the chain, the flavones. Certain members of this group of substances, the flavanone hesperidin (Fig. 5) and the formerly unknown eriodictyolglycoside, a mixture of which we had isolated from lemons and named citrin, now had the same therapeutic effect as paprika itself.

H U G O T H E O R E L L          Nobel Lecture, December 12, 1955

The nature and mode of action of oxidation enzymes

 

Practically all chemical reactions in living nature are started and directed in their course by enzymes. This being the case, Man has of course since time immemorial seen examples of what we now call enzymatic reactions, e.g. fermentation and decay. It would thus be possible to trace the history of enzymes back to the ancient Greeks, or still further for that matter. But it would be rather pointless, since to observe a phenomenon is not the same thing as to explain it. It is more correct to say that our knowledge of enzymes is essentially a product of twentieth-century research.

Jöns Jacob Berzelius, wrote in his yearbook in 1835: “…The catalytic force appears actually to consist thought herein that through their mere presence, and not through their affinity, bodies are able to arouse affinities which at this temperature are slumbering…”  Enzymes are the catalyzers of the biological world, and Berzelius’ description of catalytic force is surprisingly far-sighted…  if one could once understand the mechanism it would doubtless prove that the forces of ordinary chemistry would suffice to explain also these as yet mysterious reactions.

The year 1926 was a memorable one. The German chemist Richard Willstitter gave a lecture then in Deutsche Chemische Gesellschaft, in which he summarized the experiences gained in his attempts over many years to produce pure enzymes. Willstätter drew the conclusion that the enzymes did not belong to any known class of chemical substances, and that the effects of the enzymes derived from a new natural force, thus taking the view that 90 years earlier Berzelius thought to be improbable. That same year, through an irony of fate, the American researcher J. B. Sumner published a work in which he claimed to have crystallized in pure form an enzyme, urease. In the ensuing years J. H. Northrop and his collaborators crystallized out a further three enzyme preparations, pepsin, trypsin, and chymotrypsin, like urease, hydrolytic enzymes that split linkages by introducing water. If these discoveries had been undisputed from the outset it would probably not have been 20 years before Sumner, together with Northrop and Stanley, received a Nobel Prize.

When in 1933 I went on a Rockefeller fellowship to Otto Warburg’s institute in Berlin, Warburg and Christian had in the previous year produced a yellow-coloured preparation of an oxidation enzyme from yeast. The yellow colour was of particular interest: it faded away on reduction and returned on oxidation with e.g. oxygen, so that it was evident that the yellow pigment had to do with the actual enzymatic process of oxido-reduction. It was possible to free the yellow pigment from the high-molecular carrier substance, whose nature was still unknown, for example by treatment with acid methyl alcohol, whereupon the enzyme effect disappeared. Through simultaneous works by Warburg in Berlin, Kuhn in Heidelberg and Karrer in Zurich the constitution of the yellow pigment (lactoflavin, later riboflavin or vitamin B,) was determined. It was here for the first time possible to localize the enzymatic effect to a definite atomic constellation: hydrogen freed from the substrate (hexose monophosphate) is, with the aid of a special enzyme system (TPN-Zwischenferment) whose nature was elucidated somewhat later, placed on the nitrogen atoms of the flavin (1) and (10), giving rise to the colourless leucoflavin. This is reoxidized by oxygen, hydrogen peroxide being formed, and may afterwards be reduced again, and so forth. This cyclic process then continues until the entire amount of substrate has been deprived of two hydrogen atoms and been transformed into phosphogluconic acid; and a corresponding amount of hydrogen peroxide has been formed. At the end of the process the yellow enzyme is still there in unchanged form, and has thus apparently, as Berzelius expressed himself, aroused a chemical affinity through its mere presence.

The polysaccharides, which constituted 80-90% of the entire weight, were completely removed, together with some inactive colourless proteins. After fractionated precipitations with ammonium sulphate I produced a crystalline preparation which on ultracentrifuging and electrophoresis appeared homogeneous. The enzyme was a protein with the molecular weight 75,000 and strongly yellow-colored by the flavin part. The result of the Flavin analysis was 1 mol flavin per 1 mol protein. With dialysis against diluted hydrochloric acid at low temperature the yellow pigment was separated from the protein, which then became colorless. In the enzyme test the flavin part and the protein separately were inactive, but if the flavin part and the protein were mixed at approximately neutral reaction the enzyme effect returned, and the original effect came back when one mixed them in the molecular proportions 1 : 1. That in this connection a combination between the pigment and the protein came about was obvious, moreover, for other reasons: the green-yellow colour of the flavin part changed to pure yellow,and its strong. yellow fluorescence disappeared with linking to the protein.

In my electrophoretic experiments lactoflavin behaved as a neutral body, while the pigment part separated from the yellow enzyme moved rapidly towards the anode and was thus an acid. An analysis for phosphorus showed 1 P per mol flavin, and when after a time (1934) I succeeded in isolating the natural pigment component this proved to be a lactoflavin phosphoric acid ester, thus a kind of nucleotide, and it was obvious that the phosphoric acid served to link the pigment part to the protein. I will now show some simple experiments with the yellow enzyme, its colored part, which we now generally refer to as FMN (flavin mononucleotide), and the colorless enzyme protein.

  • The ferment-solution is pure yellow, the FMN-solution green-yellow,owing to the 1st that the light-absorption band in the blue of the free FMN is displaced somewhat in the long-wave direction on being linked with the protein component. A reducing agent (Na2S2O4) is now added to the one cuvette, it is indifferent which. The colour disappears in consequence of the formation of leucoflavin. Oxygen-gas is bubbled through the solution: the colour comes back as soon as the excess of reducing agent has been consumed. The experiment demonstrates the reaction cycle of the yellow enzyme: reduction through hydrogen from the substrate side, reoxidation with oxygen-gas.
  • A flask containing FMN-solution so diluted that its yellow color is not descernible to the eye is placed on a lamp giving long-wave ultraviolet light. The solution gives a strong, yellow fluorescence which disappears on reduction and returns on bubbling with oxygen-gas.
  • Two flasks are placed on the fluorescence lamp. The one contains a diluted solution of the free protein in phosphate buffer (pH 7), the other phosphate buffer alone. An equal amount of FMN-solution is dripped into each flask. In the flask with protein the fluorescence is at once extinguished,

but in the flask with buffer-solution alone it remains. The experiment demonstrates the resynthesis of  yellow enzyme, and since the fluorescence is extinguished by the protein, one may draw the conclusion that some group in the protein is in this connection linked to the imino-group NH(3) of the flavin, which according to Kuhn must be free for the fluorescence to appear.

The significance of these investigations on the yellow enzyme may be summarized

as follows.

  1. The reversible splitting of the yellow enzyme to apo-enzyme + coenzyme in the simple molecular relation 1 : 1 proved that we had here to do with a pure enzyme; the experiments would have been incomprehensible if the enzyme itself had been only an impurity.
  2. This enzyme was thus demonstrably a protein. In the sequel all the enzymes which have been isolated have proved to be proteins.
  3. The first coenzyme, FMN, was isolated and found to be a vitamin phosphoric acid ester. This has since proved to be something occurring widely in nature: the vitamins nicotinic acid amide, thiamine and pyridoxine form in an analogous way nucleotide-like coenzymes, which like the nucleic acids

themselves combine reversibly with proteins.

During the past 20 years a large number of flavoproteins with various enzyme effects have been produced. Instead of FMN many of them contain a dinucleotide, FAD, which consists of FMN + adenylic acid.

We constructed a very sensitive apparatus to record changes in the intensity of the fluorescence, and were thus able to follow the rapidity with which the fluorescence diminishes when FMN and protein are combined, or increases when they are split. Under suitable conditions the speed of combination is very high. Thanks to the great sensitivity of the fluorescent method my Norwegian collaborator Agnar Nygaard and I were able to make accurate determinations of the speed-constant simply by working in extremely diluted solutions, where the speed of combination is low because an FMN molecule so seldom happens to collide with a protein-molecule. We then varied the degree of acidity, ionic milieu and temperature, and we treated the protein with a large number of different reagents which affect in a known way different groups in proteins. In this way we succeeded with a rather high degree of certainty in ascertaining that phosphoric acid in FMN is linked to primary amino-groups in the protein, and the imino-group (3) in FMN to the phenolic hydroxyl group in a tyrosine residue, whereby the fluorescence is extinguished.

We still do not quite understand how through its linkage to the coenzyme the enzyme-protein “activates” the latter to a rapid absorption and giving off of hydrogen. But something we do know. The so-called oxido-reduction potential of the enzyme is in any case of great importance, and it is determined by a simple relation to the dissociation constants for the oxidized and for the reduced coenzyme-enzyme complex. The dissociation constants are in their turn functions of the velocity constants for the combination between coenzyme and enzyme and for the reverse process, and these velocity constants we have been able to determine both in the yellow ferment and in a number of enzyme systems. Without going into any details I may mention that the linkage of coenzyme to enzyme was found to have surprisingly big effects upon the potential of the former.

Alcohol dehydrogenase

 

Alcohol dehydrogenases occur in both the animal and the vegetable kingdoms, e.g. in liver, in yeast, and in peas. They are colourless proteins which together with DPN may either oxidize alcohol to aldehyde, as occurs chiefly in the liver, or conversely reduce aldehyde to alcohol, as occurs in yeast.

The yeast enzyme was crystallized by Negelein & Wulf (1936) in Warburg’s institute, the liver enzyme (from horse liver) by Bonnichsen & Wassén at our institute in Stockholm in 1948. These two enzymes have come to play a certain general rôle in biochemistry on account of the fact that it has been possible to investigate their kinetics more accurately than is the case with other enzyme systems. The liver enzyme especially, we have on repeated occasions studied with particular thoroughness, since especially favourable experimental conditions here presented themselves. For all reactions with DPN-system it is possible to follow the reaction DPN+ + 2H =+ DPNH + H+ spectrophotometrically, since DPNH has an absorption-band in the more long-wave ultraviolet region, at 340 rnp, and thousands of such experiments have been performed all over the world. A couple of years ago, moreover, we began to apply our fluorescence method, which is based on the fact that DPNH but not DPN fluoresces, even if considerably more weakly than the flavins. Asregards the liver enzyme there is a further effect, which proved extremely useful for certain spectrophotometrical determinations of reaction speeds; together with Bonnichsen I found in 1950 that the 340 rnp band of the reduced coenzyme was displaced, on combination with liver alcohol dehydrogenase, to 325 rnp, and together with Britton Chance we were thus able with the help of his extremely refined rapid spectrophotometric methods to determine the velocity constant for this very rapid reaction. This reaction belongs to the 3 bost problem involving the enzyme, the coenzyme, and the substrate, and both the coenzyme and the substrate occur in both oxidized and reduced forms.

It is a curious whim of nature that the same coenzyme which in the yeast makes alcohol by attaching hydrogen to aldehyde also occurs in the liver to remove from alcohol the same hydrogen, so that the alcohol becomes aldehyde again, which is then oxidized further
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Heme proteins

In 1936 we had obtained cytochrome approximately 80% pure, and in 1939 close to 100%.It is a beautiful red, iron-porphyrin-containing protein which functions as a link in the chain of the cell-respiration enzymes, the iron atom now taking up and now giving off an electron, and the iron thus alternating valency between the 3-valent ferri and the 2-valent ferro stages. It is a very pleasant substance to work with, not merely because it is lovely to look at, but also because it is uncommonly stable and durable. From 100 kg horse heart one can produce 3-4 grams of pure cytochrome c. The molecule weighs about 12,000 and contains one mol iron porphyrin per-mol.

Exp. 4. Two cuvettes each contain a solution of ferricytochrome c. The colour is blood-red. To the one are added some grains of sodium hydrosulphite: the color is changed to violet-red (ferrocytochrome). Oxygen is now bubbled through the ferrocytochrome-solution: no visible change occurs. The ferrocyto-chrome can thus not be oxidized by oxygen. A small amount of cytochrome oxidase is now added: the ferricytochrome color returns.

From this experiment we can draw the conclusion that reduced cytochrome c cannot react with molecular oxygen. In a chain of oxidation enzymes it will thus not be able to be next to the oxygen. The incapacity of cytochrome to react with oxygen was a striking fact that required an explanation. Another peculiarity was the extremely firm linkage between the red heme pigment and the protein part; in contradistinction to the majority of other heme protides, the pigment cannot be split off by the addition of acetone acidified with hydrochloric acid. Further, there was a displacement of the light-absorption bands which indicated that the two unsaturated vinyl groups occurring in ordinary protohemin were saturated in the hematin of

the cytochrome. In 1938 we succeeded in showing that the porphyrin part of the cytochrome was linked to the protein by means of two sulphur bridges from cysteine residues in the protein of the porphyrin in such a way that the vinyl groups were saturated and were converted to α-thioether groups. The firmness of the linkage and the displacement of the spectral bands were herewith explained. This was the first time that it had been possible to show the nature of chemical linkages between a “prosthetic” group (in this case iron porphyrin) and the protein part in an enzyme.

The light-absorption bands of the cytochrome showed that it is a so-called hemochromogen, which means that two as a rule nitrogen-containing groups are linked to the iron, in addition to the four pyrrol-nitrogen atoms in the porphyrin. From magnetic measurements that I made at Linus Pauling’s institute in Pasadena and from amino-acid analyses, titration curves and spectrophotometry together with Å. Åkeson it emerged (1941) that the nitrogen-containing, hemochromogen-forming groups in cytochrome c were histidine residues, or to be more specific, their imidazole groups.   Recently we have got a bit farther. Tuppy & Bodo in Vienna began last year with Sanger’s method to elucidate the amino-acid sequence in the hemin-containing peptide fragment that one obtains with the proteolytic breaking down of cytochrome c, and succeeded in determining the sequence of the amino acids nearest the heme. The experiments were continued and supplemented by Tuppy, Paléus & Ehrenberg at our institute in Stockholm with the following result:

The peptide chain 1-12 (“Val”) = the amino acid valine, “Glu” = glutamine,”Lys” = lysine, and so forth) is by means of two cysteine-S-bridges and a linkage histidine-Fe linked to the heme. When in 1954 Linus Pauling delivered his Nobel Lecture in Stockholm he showed a new kind of models for the study of the steric configuration of peptide chains, which as we know may form helices or “pleated sheets” of various kinds. It struck me then that it would be extremely interesting to study the question as to which of these possibilities might be compatible with the sulphur bridges to the hemin part and with the linkage of nitrogen containing groups to the iron. Pauling was kind enough to make me a present of his peptide-model pieces, which I shall show presently. This is thus the second time they figure in a Lecture.

Anders Ehrenberg and I now made a hemin model on the same scale as the peptide pieces and constructed models of hemin peptides with every conceivable variant of hydrogen bonding. It proved that many variants could be definitely excluded on steric grounds, and others were improbable for other reasons. Of the original, at least 20 alternatives, finally only one remained – a left-twisting a-helix with the cysteine residue no. 4 linked to the porphyrin side-chain in 4-position, and cysteine no. 7 to the side-chain in 2-position. The imidazole residue fitted exactly to linkage with the iron atom. The peptide spiral becomes parallel with the plane of the heme disc.

Through calculations on the basis of the known partial specific volume of the cytochrome we now consider it extremely probable that the heme plate in cytochrome c is surrounded by peptide spirals on all sides in such a way that the heme iron is entirely screened off from contact with oxygen; here is the explanation of our experiment in which we were unable to oxidize reduced cytochrome c with oxygen-gas. The oxygen simply cannot get at the iron atom. There is, on the other hand, a possibility for electrons to pass in and out in the iron atom via the imidazole groups.  It strikes us as interesting that even at this stage the special mode of reacting of the cytochrome is beginning to be understood from what we know of its chemical constitution.

F r i t z  L i p m a n n           Nobel Lecture, December 11, 1953

Development of the acetylation problem: a personal account

 

In my development, the recognition of facts and the rationalization of these facts into a unified picture, have interplayed continuously. After my apprenticeship with Otto Meyerhof, a first interest on my own became the phenomenon we call the Pasteur effect, this peculiar depression of the wasteful fermentation in the respiring cell. By looking for a chemical explanation of this economy measure on the cellular level, I was prompted into a study of the mechanism of pyruvic acid oxidation, since it is at the pyruvic stage where respiration branches off from fermentation. For this study I chose as a promising system a relatively simple looking pyruvic acid oxidation enzyme in a certain strain of Lactobacillus delbrueckii1. The decision to explore this particular reaction started me on a rather continuous journey into partly virgin territory to meet with some unexpected discoveries, but also to encounter quite a few nagging disappointments

The most important event during this whole period, I now feel, was the accidental observation that in the L. delbrueckii system, pyruvic acid oxidation was completely dependent on the presence of inorganic phosphate. This observation was made in the course of attempts to replace oxygen by methylene blue. To measure the methylene blue reduction manometrically, I had to switch to a bicarbonate buffer instead of the otherwise routinely used phosphate. In bicarbonate, to my surprise, as shown in Fig. 1, pyruvate oxidation was very slow, but the addition of a little phosphate caused a  remarkable increase in rate. The next figure, Fig. 2, shows the phosphate effect more drastically, using a preparation from which all phosphate was removed by washing with acetate buffer. Then it appeared that the reaction was really fully dependent on phosphate. In spite of such a phosphate dependence, the phosphate balance measured by the ordinary Fiske-Subbarow procedure did not at first indicate any phosphorylative step. Nevertheless, the suspicion remained that phosphate in some manner was entering into the reaction and that a phosphorylated intermediary was formed. As a first approximation, a coupling of this pyruvate

oxidation with adenylic acid phosphorylation was attempted. And, indeed, addition of adenylic acid to the pyruvic oxidation system brought out a net disappearance of inorganic phosphate, accounted for as adenosine triphosphate (Table 11). In parallel with the then just developing fermentation now concluded that the missing link in the reaction chain was acetyl phosphate. In partial confirmation it was shown that a crude preparation of acetyl phosphate, synthesized by the old method of Kämmerer and Carius2

would transfer phosphate to adenylic acid (Table 2). However, it still took quite some time from then on to identify acetyl phosphate definitely as the initial product of the pyruvic oxidation in this system3,4.

At the time when these observations were made, about a dozen years ago, there was, to say the least, a tendency to believe that phosphorylation was rather specifically coupled with the glycolytic reaction. Here, however, we had found a coupling of phosphorylation with a respiratory system. This observation immediately suggested a rather sweeping biochemical significance, of transformations of electron transfer potential, respiratory or fermentative, to phosphate bond energy and therefrom to a wide range of biosynthetic reactions7.

There was a further unusual feature in this pyruvate oxidation system in that the product emerging from the process not only carried an energy-rich phosphoryl radical such as already known, but the acetyl phosphate was even more impressive through its energy-rich acetyl. It rather naturally became a contender for the role of “active” acetate, for the widespread existence of which the isotope experience had already furnished extensive evidence. I became, therefore, quite attracted by the possibility that acetyl phosphate could serve two rather different purposes, either to transfer its phosphoryl group into the phosphate pool, or to supply its active acetyl for biosynthesis of carbon structures. Thus acetyl phosphate should be able to serve as acetyl donor as well as phosphoryl donor, transferring, as shown in Fig. 3, on either side of the oxygen center, such as indicated by Bentley’s early experiments on cleavage7a of acetyl phosphate in H2 18O.

These two novel aspects of the energy problem, namely

(1) the emergence of an energy-rich phosphate bond from a purely respiratory reaction; and

(2) the presumed derivation of a metabolic building-block through this same there towards a general concept of transfer of activated groupings by carrier as the fundamental reaction in biosynthesis8,9.

Although in the related manner the appearance of acetyl phosphate as a metabolic intermediary first

focussed attention to possible mechanisms for the metabolic elaboration of group activation, it soon turned out that the relationship between acetyl phosphate and acetyl transfer was much more complicated than anticipated. reaction, prompted me to propose

  • not only the generalization of the phosphate bond as a versatile energy distributing system,
  • but also to aim there towards a general concept of transfer of activated groupings by carrier as the fundamental reaction in biosynthesis8,9.

Although in the related manner the appearance of acetyl phosphate as a metabolic intermediary first focussed attention to possible mechanisms for the metabolic elaboration of group activation, it soon turned out that the relationship between acetyl phosphate and acetyl transfer was much more complicated than anticipated.

It appeared that as an energy source the particle bound oxidative phosphorylation of the kind observed first by Herman Kalckar14 could be replaced by ATP, as had first been observed with the acetylation of choline in brain preparations by Nachmansohn and his group15,16. Using ATP and acetate as precursors, it was possible to set up a homogeneous particle-free acetylation system obtained by extraction of acetone pigeon liver. In this extract acetyl phosphate was unable to replace the ATP acetate as acetyl precursor.

In spite of this disappointment with acetyl phosphate, our decision to turn to a study of acetylation started then to be rewarding in another way. During these studies we became aware of the participation of a heat-stable factor which disappeared from our enzyme extracts on aging or dialysis. This cofactor was present in boiled extracts of all organs, as well as in microorganisms and yeast. It could not be replaced by any other known cofactor. Therefore, it was suspected that we were dealing with a new coenzyme. From then on, for a number of years, the isolation and identification of this coenzyme became the prominent task of our laboratory. The problem now increased in volume and I had the very good fortune that a group of exceedingly able people were attracted to the laboratory; first Constance Tuttle, then Nathan O. Kaplan and shortly afterwards, G. David Novelli, and then others.

Early data on the replacement of this heat-stable factor by boiled extracts are shown in the next table (Table 3). The pigeon liver acetylation system proved to be a very convenient assay system for the new coenzyme17 since on aging for 4 hours at room temperature, the cofactor was completely autolyzed.

Fortunately, on the other hand, the enzyme responsible for the decomposition of this factor was quite unstable and faded out during the aging, while the acetylation apoenzymes were unaffected.

The next figure, Fig. 4, shows coenzyme A (CoA) assay curves obtained with acetone pigeon liver extract. Finding pig liver a good source for the coenzyme, we set out to collect a reasonably large quantity of a highly purified preparation and then to concentrate on the chemistry with this material. In this analysis we paid particular attention to the possibility of finding in this obviously novel cofactor one of the vitamins.

The subsequence finding of a B-vitamin in the preparation gave us further confidence that we were dealing here with a key substance. We still felt, however, slightly dissatisfied with the proof for pantothenic acid. Therefore, to liberate the chemically rather unstable pantothenic acid from CoA, we made use of observations on enzymatic cleavage of the coenzyme. Two enzyme preparations, intestinal phosphatase and an enzyme in pigeon liver extract, had caused independent inactivation. It then was found that through combined action of these two enzymes, pantothenic acid was liberated18,19.

The two independent enzymatic cleavages indicated early that in CoA existed two independent sites of attachment to the pantothenic acid molecule. One of these obviously was a phosphate link, linking presumably to one of a hydroxyl group in pantothenic acid. The other moiety attached to pantothenic acid, which, cleaved off by liver enzyme, remained unidentified for a long time. In addition to pantothenic acid, our sample of 40 per cent purity had been found to contain about 2 per cent sulfur by elementary analysis and identified by cyanide-nitroprusside test as a potential SH grouping 20,21. Furthermore, the coenzyme preparation contained large amounts of adenylic acid21.

Units Coenzyme

Fig. 4. Concentration-activity curves for coenzyme A preparations of different purity. The arrow indicates the point of 1 unit on the curve. (o) crude coenzyme, 0.25 unit per mg; (x) purified coenzyme, 130 units per mg.

In the subsequent elaboration of the structure, the indications by enzyme analysis for the two sites of attachment to pantothenic acid have been most helpful. The phosphate link was soon identified as a pyrophosphate bridge22; 5-adenylic acid was identified by Novelli23 as enzymatic split product and by Baddiley 24, through chemical cleavage. At the same time, Novelli made observations which indicated the presence of a third phosphate in addition to the pyrophosphate bridge. These indications were confirmed by analysis of a nearly pure preparation which was obtained by Gregoryas from Streptomyces fradiae in collaboration with the research group at the Upjohn Company26.

It was at this period that we started to pay more and more attention to the sulfur in the coenzyme. As shown in Table 5, our purest preparation contained 4.13 per cent sulfur corresponding to one mole per mole of pantothenate. We also found26 that dephosphorylation of CoA yielded a compound containing pantothenic acid and the sulfur carrying moiety, which we suspected as bound through the carboxyl. Through the work of Snell and his group27, the sulfur-containing moiety proved to be attached to pantothenic acid through a link broken by our liver enzyme. It was identified as thioethanolamine by Snell and his group, linked peptidically to pantothenic acid.

Through analysis and synthesis, Baddiley now identified the point of attachment of the phosphate bridge to pantothenic acid in 4-position24 and Novelli et al.28 completed the structure analysis by enzymatic synthesis of “dephospho-CoA” from pantetheine-4’-phosphates and ATP. Furthermore, the attachment of the third phosphate was identified by Kaplan29 to attach in s-position on the ribose of the 5-adenylic acid (while in triphosphopyridine nucleotide it happens to be in 2-position). Therefore, the structure was now

established, as shown in Fig. 5.

Fig. 5. Structure of coenzyme A

 

The metabolic function of CoA


Parallel with this slow but steady elaboration of the structure, all the time we explored intensively metabolic mechanisms in the acetylation field. By use of the enzymatic assay, as shown in Tables 6, 7, 8, and 9, CoA was found present in all living cells, animals, plants and microorganisms17. Furthermore,

the finding that all cellular pantothenic acid could be accounted for by CoA17 made it clear that CoA represented the only functional form of this vitamin. The finding of the vitamin furnished great impetus; nevertheless, a temptation to connect the pantothenic acid with the acetyl transfer function has

blinded us for a long time to other possibilities.

The first attempts to further explore the function of CoA were made with pantothenic acid-deficient cells and tissues. A deficiency of pyruvate oxidation in pantothenic acid-deficient Proteus morganii, an early isolated observation by Dorfman30 and Hills31, now fitted rather well into the picture. We soon became quite interested in this effect, taking it as an indication for participation of CoA in citric acid synthesis. A parallel between CoA levels and pyruvate oxidation in Proteus morganii was demonstrated32. Using panto thenic aciddeficient yeast, Novelli et al.33 demonstrated a CoA-dependence of acetate oxidation (Fig. 5a) and Olson and Kaplan34 found with duck liver a striking parallel between CoA content and pyruvic utilization, which is shown in Fig. 6.

But more important information was being gathered on -the enzymatic level. The first example of a generality of function was obtained by comparing the activation of apoenzymes for choline- and sulfonamide-acetylation respectively, using our highly purified preparations9 of CoA. As shown in Fig. 7, similar activation curves obtained for the two respective enzymes. Through these experiments, the heat-stable factor for choline acetylation that had been found by Nachmansohn and Berman35 and by Feldberg and Mann36 was identified with CoA. The next most significant step toward a generalization of CoA function for acetyl transfer was made by demonstrating its functioning in the enzymatic synthesis of acetoacetate. The CoA effect in acetoacetate synthesis was studied by Morris Soodak37, who obtained for this reaction a reactivation curve quite similar to those for enzymatic acetylation, as shown in Fig. 8.

Soon afterwards Stern and Ochoa38 showed a CoA-dependent citrate synthesis with a pigeon liver fraction similar to the one used by Soodak for acetoacetate synthesis. In our laboratory, Novelli et al. confirmed and extended this observation with extracts of Escherichia coli39.

In the course of this work, which more and more clearly defined the acetyl transfer function of CoA, Novelli once more tried acetyl phosphate. To our surprise and satisfaction, it then appeared, as shown in Table 9, that in Escherichia coli extracts in contrast to the animal tissue, acetyl phosphate was more than twice as active as acetyl donor for citrate synthesis than ATP acetate 39. Acetyl phosphate, therefore, functioned as a patent microbial acetyl donor. Acetyl transfer from acetyl phosphate, like that from ATP-acetate, was CoA-dependent, as shown in Table 9. Furthermore, a small amount of “microbial conversion factor”, as we called it first, primed acetyl phosphate for activity with pigeon liver acetylation systems40, as shown in Table 10.

Eventually the microbial conversion factor was identified by Stadtman et al.40 with the transacetylase first encountered by Stadtman and Barker in extracts of Clostridium kluyveri41 and likewise, although not clearly defined as such, in extracts of Escherichia coli and Clostridium butylicum by Lipmann and Tuttle42. The definition of such a function was based on the work of Doudoroff et al.43 on transglucosidation with sucrose phosphorylase. Their imaginative use of isotope exchange for closer definition of enzyme mechanisms has been most influential. Like glucose-I-phosphate with sucrose phosphorylase, acetyl phosphate with these various microbial preparations equilibrates its phosphate rapidly with the inorganic phosphate of the solution. As in Doudoroff et al. experiments, first a covalent substrate enzyme derivative had been proposed 43. However, then Stadtman et al.40, with the new experience of CoA dependent acetyl transfer, could implicate CoA in this equilibration between acetyl- and inorganic phosphate and thus could define the transacetylase as an enzyme equilibrating acetyl between phosphate and CoA:

In the course of these various observations, it became quite clear that there existed in cellular metabolism an acetyl distribution system centering around CoA as the acetyl carrier which was rather similar to the ATP-centered phosphoryl distribution system. The general pattern of group transfer became recognizable, with donor and acceptor enzymes being connected through the CoA —- acetyl CoA shuttle. A clearer definition of the donor-acceptor enzyme scheme was obtained through acetone fractionation of our standard system for acetylation of sulfonamide into two separate enzyme fractions, which were inactive separately but showed the acetylation effect when combined. A fraction, A-40, separating out with 40 per cent acetone, was shown by Chou44 to contain the donor enzyme responsible for the ATP-CoA-acetate reaction, while with more acetone precipitated, the acceptor function, A-60, the acetoarylamine kinase as we propose to call this type of enzyme. The need for a combination of the two for overall acetyl transfer is shown in Fig. 9. This showed that a separate system was responsible for acetyl CoA formation through interaction of ATP, CoA and acetate (cf. below) and that the overall acetylation was a two-step reaction:

These observations crystallized into the definition of a metabolic acetyl transfer territory as pictured in Fig. 10. This picture had developed from the growing understanding of enzymatic interplay involving metabolic generation of acyl CoA and transfer of the active acyl to various acceptor systems. A most important, then still missing link in the picture was supplied through the brilliant work of Feodor Lynen45 who chemically identified acetyl CoA as the thioester of CoA. Therewith the thioester link was introduced as a new energy-rich bond and this discovery added a very novel facet to our understanding of the mechanisms of metabolic energy transformation.

Enzyme Localization In The  Anaerobic Mitochondria Of Ascaris L Umbricoides

 

Robert S. Rew And Howard J. Saz

From the Department of Biology, University of Notre Dame, Notre Dame, Indiana 46556

 

Mitochondria from the muscle of the parasitic nematode Ascaris lumbricoides   var. suum function anaerobically in electron transport-associated  phosphorylations under physiological conditions. These helminth organelles have been fractionated into inner and outer membrane, matrix, and intermembrane space fractions. The distributions of enzyme systems were determined and compared with corresponding distributions reported in mammalian mitochondria.  Succinate and pyruvate dehydrogenases as well as NADH  oxidase, Mg++-dependent ATPase, adenylate kinase, citrate synthase, and cytochrome c  reductases  were  determined to be distributed  as  in mammalian mitochondria.  In contrast  with  the  mammalian systems, fumarase and NAD-linked “malic” enzyme were isolated primarily from the intermembrane  space fraction of the worm mitochondria. These enzymes required for the anaerobic  energy-generating system in Ascaris and would be expected to give rise to NADH in the intermembrane space.  The need for and possible mechanism of a proton translocation system to obtain energy generation is suggested.                                Downloaded from jcb.rupress.org

                                                                                                                                                      

                          

                               

                               

                               

                               

David Keilin’s Respiratory Chain Concept and its Chemiosmotic Consequences

Peter Mitchell              Nobel Lecture, 8 December, 1978

Glynn Research Institute, Bodmin, Cornwall, U. K.
“for his contribution to the understanding of biological energy transfer through the formulation of the chemiosmotic theory”

Peter D. Mitchell (1920-1992) received the Nobel Prize in 1978 for developing the Chemiosmotic Theory to explain ATP synthesis resulting from membrane-associated electron transport [Ubiquinone and the Proton Pump].

Mitchell is the last of the gentleman scientists. He first proposed the chemiosmotic principle in a 1961 Nature article while he was at the University of Edinburgh. Shortly after that, ill health forced him to move to Cornwall where he renovated an old manor house and converted it into a research laboratory. From then on, he and his research colleague, Jennifer Moyle, continued to work on the chemiosmotic theory while being funded by his private research foundation. [Peter Mitchell: Wikipedia]

The Chemiosmotic Theory was controversial in 1978 and it still has not been fully integrated into some biochemistry textbooks in spite of the fact that it is now proven. The main reason for the resistance is that it overthrows much of traditional biochemistry and introduces a new way of thinking. It is a good example of a “paradigm shift” in biology.

Because he was such a private, and eccentric, scientist there are very few photos of Peter Mitchell or his research laboratory at Glynn House . The best description of him is in his biography Wandering in the Gardens of the Mind: Peter Mitchell and the Making of Glynn by John Prebble, and Bruce Weber. A Nature review by E.C. Slater [Metabolic Gardening] gives some of the flavor and mentions some of the controversy.

Wandering_in_the_Gardens_of_the_Mind_Peter_Mitchell

Wandering_in_the_Gardens_of_the_Mind_Peter_Mitchell

Peter_Mitchell

Peter_Mitchell

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Many scientists believe that the Chemiosmotic Theory was the second greatest contribution to biology in the 2oth century (after the discovery of the structure of DNA). Mitchell had to overcome many critics including Hans Krebs. The case is strong.

In the 1960s, ATP was known to be the energy currency of life, but the mechanism by which ATP was created in the mitochondria was assumed to be by substrate-level phosphorylation. Mitchell’s chemiosmotic hypothesis was the basis for understanding the actual process of oxidative phosphorylation. At the time, the biochemical mechanism of ATP synthesis by oxidative phosphorylation was unknown.

Mitchell realised that the movement of ions across an electrochemical potential difference could provide the energy needed to produce ATP. His hypothesis was derived from information that was well known in the 1960s. He knew that living cells had a membrane potential; interior negative to the environment. The movement of charged ions across a membrane is thus affected by the electrical forces (the attraction of positive to negative charges). Their movement is also affected by thermodynamic forces, the tendency of substances to diffuse from regions of higher concentration. He went on to show that ATP synthesis was coupled to this electrochemical gradient.[11]

His hypothesis was confirmed by the discovery of ATP synthase, a membrane-bound protein that uses the potential energy of the electrochemical gradient to make ATP.

Growth, development and metabolism are some of the central phenomena in the study of biological organisms. The role of energy is fundamental to such biological processes. The ability to harness energy from a variety of metabolic pathways is a property of all living organisms. Life is dependent on energy transformations; living organisms survive because of exchange of energy within and without.

In a living organism, chemical bonds are broken and made as part of the exchange and transformation of energy. Energy is available for work (such as mechanical work) or for other processes (such as chemical synthesis and anabolic processes in growth), when weak bonds are broken and stronger bonds are made. The production of stronger bonds allows release of usable energy.

One of the major triumphs of bioenergetics is Peter D. Mitchell‘s chemiosmotic theory of how protons in aqueous solution function in the production of ATP in cell organelles such as mitochondria.[5] This work earned Mitchell the 1978 Nobel Prize for Chemistry. Other cellular sources of ATP such as glycolysis were understood first, but such processes for direct coupling of enzyme activity to ATP production are not the major source of useful chemical energy in most cells. Chemiosmotic coupling is the major energy producing process in most cells, being utilized in chloroplasts and several single celled organisms in addition to mitochondria.

Cotransport

In August 1960, Robert K. Crane presented for the first time his discovery of the sodium-glucose cotransport as the mechanism for intestinal glucose absorption.[2] Crane’s discovery of cotransport was the first ever proposal of flux coupling in biology and was the most important event concerning carbohydrate absorption in the 20th century.[3][4]

The free energy (ΔG) gained or lost in a reaction can be calculated: ΔG = ΔH – TΔS
where G = Gibbs free energy, H = enthalpy, T = temperature, and S = entropy.

How inositol pyrophosphates control cellular phosphate homeostasis?

Adolfo Saiardi*

Cell Biology Unit, Medical Research Council Laboratory for Molecular Cell Biology, Department of Cell and Developmental Biology,

University College London, Gower Street, London WC1E 6BT, United Kingdom

Advances in Biological Regulation 52 (2012) 351–359

Phosphorus in his phosphate PO43_ configuration is an essential constituent of all life forms. Phosphate diesters are at the core of nucleic acid structure, while phosphate monoester transmits information under the control of protein kinases and phosphatases. Due to these fundamental roles in biology it is not a surprise that phosphate cellular homeostasis is under tight control.

Inositol pyrophosphates are organic molecules with the highest proportion of phosphate groups, and they are capable of regulating many biological processes, possibly by controlling energetic metabolism and adenosine triphosphate (ATP) production.

Furthermore, inositol pyrophosphates influence inorganic polyphosphates (polyP) synthesis. The polymer polyP is solely constituted by phosphate groups and beside other known functions, it also plays a role in buffering cellular free phosphate [Pi] levels, an event that is ultimately necessary to generate ATP and inositol pyrophosphate.

Two distinct classes of proteins the inositol hexakisphosphates kinases (IP6Ks) and the diphosphoinositol pentakisphosphate kinases (PP-IP5Ks or IP7Ks) are capable of synthesizing inositol pyrophosphates.

IP6Ks utilize ATP as a phosphate donor to phosphorylate IP6 to IP7, generation the isomer 5PP-IP5 (Fig. 1A), and inositol pentakisphosphate I(1,3,4,5,6)P5 to PP-IP4 (Saiardi et al., 1999, 2000; Losito et al., 2009). Furthermore, at least in vitro, IP6Ks generate more complex molecules containing two or more pyrophosphate moieties, or even three-phosphate species (Draskovic et al., 2008; Saiardi et al., 2001). Three IP6K isoforms referred to as IP6K1, 2, 3 exist in mammal; however, there is a single IP6K in the yeast Saccharomyces cerevisiae called Kcs1.

The PP-IP5Ks enzymes, synthesize inositol pyrophosphate from IP6, but not from IP5, (Losito et al., 2009) generating the isomer 1PP-IP5. Kinetic studies performed in vitro suggested that IP7, the 5PP-IP5 isomer generated by IP6Ks, is the primary substrate of this new enzyme, and this finding was confirmed in vivo by analysing PP-IP5K null yeast (vip1D) that accumulate the un-metabolized substrate IP7 (Azevedo et al., 2009; Onnebo and Saiardi, 2009). Thus PP-IP5K is responsible for IP8,

isomer 1,5PP2-IP4 synthesis (Fig. 1A). Two PP-IP5K isoforms referred to as PP-IP5Ka and b exist in mammal while a single PP-IP5K called Vip1 is present in S. cerevisiae.

Inositol pyrophosphates are hydrolysed by the diphosphoinositol-polyphosphate phosphohydrolases (DIPPs) (Safrany et al., 1998). Four mammalian enzymes DIPP1,2,3,4 have been identified, while only one DIPP protein exists in S. cerevisiae called Ddp1. These phosphatases are promiscuous enzymes able to hydrolyse inositol pyrophosphate as well as nucleotide analogues, such as diadenosine hexaphosphate (Ap6A) (Caffrey et al., 2000; Fisher et al., 2002). More recently, it has been shown that DIPPs also degrade polyP (Lonetti et al., 2011). Inositol pyrophosphates control the most disparate biological processes, from telomere length to vesicular trafficking. It is conceivable that all these function can be focused on the fact that inositol pyrophosphates are controlling cellular energy metabolism and consequently, ATP production. We have recently, demonstrated that inositol pyrophosphates control glycolysis and mitochondrial oxidative phosphorylation by both inhibiting the glycolytic flux and increasing mitochondrial activity (Szijgyarto et al., 2011).

Another important molecule to briefly introduce is polyP (Fig. 1B). The interested reader is encouraged to read the following comprehensive reviews (Kornberg et al., 1999; Rao et al., 2009). The polyP polymer likely represents a phosphate buffer that is synthesized and degraded in function of the phosphate needs of the cells. Furthermore, it also functions as a chelator of metal ions, thereby regulating cellular cation homeostasis. However, polyP also possesses more classical signalling roles.

In bacteria for example, it influences pathogenicity (Brown and Kornberg, 2008) and in mammalian cells it has been proposed to regulate fibrinolysis and platelet aggregation (Caen and Wu, 2010). In prokaryotes, polyP synthesis is carried out by a family of conserved polyP kinases (PPKs), whereas degradation is mediated by several polyP phosphatases (Rao et al., 2009). In higher eukaryotes polyP synthesis remains poorly characterized.

In humans alteration of phosphate metabolism is implicated in several pathological states. Higher serum phosphate leads to vascular calcification and cardiovascular complications. Although only very small amount of phosphate circulates in the serum, its concentration is tightly regulated and it is independent from dietary phosphorus intake (de Boer et al., 2009). Therefore, it is not surprising that intense research efforts are aimed to elucidate phosphate uptake and metabolism. IP6K2 was initially cloned while searching for a novel mammalian intestinal phosphate transporter that the group of Murer identified as PiUS (Phosphate inorganic Uptake Stimulator) (Norbis et al., 1997). Once transfected into Xenopus oocytes, PiUS stimulated the cellular uptake of radioactive phosphate.

Subsequently, two groups discovered that PiUS was capable of converting IP6 to IP7 and rename it to IP6K2 (Saiardi et al., 1999; Schell et al., 1999). The ability of inositol pyrophosphate to control the uptake of phosphate is an evolutionary conserved feature; in fact, kcs1D yeast with undetectable level of IP7 exhibits a reduced uptake of phosphate from the culture medium (Saiardi et al., 2004).

In mammals, regulation of phosphate homeostasis is not restricted to IP6K2, all three mammalian IP6Ks are likely to play a role. A genome-wide study aimed at identifying genetic variations associated with changes of serum phosphorus concentration identified IP6K3 (Kestenbaum et al., 2010). This human genetic study identified two independent single nucleotide polymorphisms (SNP) at locus 6p21.31, which are localised within the first intron of the IP6K3 gene. Interestingly, this study that analysed more than 16,000 humans identified SNP variant in only seven genes. Three of which, the sodium phosphate cotransporter type IIa, the calcium sensing receptor and the fibroblast growth factor 23, are well known regulators of phosphate homeostasis. These evidences support a role for IP6K3 in controlling serum phosphate levels in humans (Kestenbaum et al., 2010).

 

The hypothesis

 

Although, inositol pyrophosphate may have acquired unique organism-specific functions, the conserved ability of this class of molecules to regulate phosphate metabolism suggests an evolutionary ancient role. In this last paragraph, I will formulate few hypotheses that I hope will stimulate further research aimed at elucidating the biological link between phosphate, inositol pyrophosphates and polyP.

Inositol pyrophosphates regulate the entry of phosphate into the cells (Norbis et al., 1997), suggesting that they could affect phosphate uptake either directly (by stimulating a transporter, for example) or a indirectly by helping ‘fixing’ free phosphates in organic molecules. The cytosolic concentration of free phosphate [Pi] cannot fluctuate widely. Therefore, cellular entry of phosphates and its utilization may well be coupled. For example, the synthesis of polyP may be linked to phosphate entry in the cell. Inositol pyrophosphate control of energy metabolism (Szijgyarto et al., 2011) affects not only ATP levels but it can also alter the entire cellular balance of adenine nucleotides. Given that phosphate transfer reactions mainly use ATP as a vehicle for the phosphate groups, inositol pyrophosphate could affect phosphate metabolism by regulating the adenylate cellular pool. Moreover, it is tempting to speculate the existence of a feedback mechanism that coordinates the metabolic balance between ATP, phosphate and inositol pyrophosphates.

Inositol pyrophosphates could either contribute to the regulation of polyP synthesis, play a role in polyP degradation, or both. The yeast polyP polymerase has been identified with the subunit four (Vtc4) of the vacuolar membrane transporter chaperone (VTC) complex (Hothorn et al., 2009). Interestingly, pyrophosphates (Pi–Pi) dramatically accelerate the polyP polymerase reaction. It would therefore be interesting to determine whether the pyrophosphate moiety of IP7 can stimulate polyP vacuolar synthesis in a similar fashion. Similarly, it would be interesting to analyse the effect of inositol pyrophosphates on controlling the activity of the actin-like DdIPK2 enzyme. It should be noted however, that the existence even in yeast or Dictyostelium of other enzymes able to synthesize different polyP pools cannot be excluded. Thus, we will be able to validate and fully appreciate the role played by inositol pyrophosphates on polyP synthesis only after the identification of higher eukaryotes polyp synthesizing peptide/s.

The most abundant form of organic phosphate on earth is IP6, or phytic acid, a molecule that is highly abundant in plant seeds from which was originally characterised. In plant seeds, IP6 represents a phosphate storage molecule that it is hydrolysed during germination, releasing phosphates and cations. It will be an astonishing twist of event if inositol pyrophosphates were controlling the levels of their own precursor IP6 (Raboy, 2003), although due to the evolutionary conserved ability of inositol pyrophosphate to control phosphate homeostasis we should not be entirely surprised.

Although it is not yet clear how inositol pyrophosphates regulate cellular metabolism, understanding how inositol pyrophosphates influence phosphates homeostasis will help to clarify this important link.

Auesukaree C, Tochio H, Shirakawa M, Kaneko Y, Harashima S. Plc1p, Arg82p, and Kcs1p, enzymes involved in inositol pyrophosphate synthesis, are essential for phosphate regulation and polyphosphate accumulation in Saccharomyces cerevisiae. J Biol Chem 2005;280:25127–33.

Azevedo C, Burton A, Ruiz-Mateos E, Marsh M, Saiardi A. Inositol pyrophosphate mediated pyrophosphorylation of AP3B1 regulates HIV-1 Gag release. Proc Natl Acad Sci U S A 2009;106:21161–6.

Bennett M, Onnebo SM, Azevedo C, Saiardi A. Inositol pyrophosphates: metabolism and signaling. Cell Mol Life Sci 2006;63:552–64.

Boer VM, Crutchfield CA, Bradley PH, Botstein D, Rabinowitz JD. Growth-limiting intracellular metabolites in yeast growing under diverse nutrient limitations. Mol Biol Cell 2010;21:198–211.

Brown MR, Kornberg A. The long and short of it – polyphosphate, PPK and bacterial survival. Trends Biochem Sci 2008;33:284–90.

Burton A, Hu X, Saiardi A. Are inositol pyrophosphates signalling molecules? J Cell Physiol 2009;220:8–15.

Caen J, Wu Q. Hageman factor, platelets and polyphosphates: early history and recent connection. J Thromb Haemost 2010;8:1670–4.

Caffrey JJ, Safrany ST, Yang X, Shears SB. Discovery of molecular and catalytic diversity among human diphosphoinositol polyphosphate phosphohydrolases. An expanding Nudt family. J Biol Chem 2000;275:12730–6.

A Mitochondrial RNAi Screen Defines Cellular Bioenergetic Determinants and Identifies an Adenylate Kinase as a Key Regulator of ATP Levels

Nathan J. Lanning,1 Brendan D. Looyenga,1,2 Audra L. Kauffman,1 Natalie M. Niemi,1 Jessica Sudderth,3

Ralph J. DeBerardinis,3 and Jeffrey P. MacKeigan1,*

Cell Reports   http://dx.doi.org/10.1016/j.celrep.2014.03.065

Altered cellular bioenergetics and mitochondrial function are major features of several diseases, including cancer, diabetes, and neurodegenerative disorders. Given this important link to human health, we sought to define proteins within mitochondria that are critical for maintaining homeostatic ATP levels.

We screened an RNAi library targeting >1,000 nuclear-encoded genes whose protein products localize to the mitochondria in multiple metabolic conditions in order to examine their effects on cellular ATP levels. We identified a mechanism by which electron transport chain (ETC) perturbation under glycolytic conditions increased ATP production through enhanced glycolytic flux, thereby highlighting the cellular potential for metabolic plasticity.

Additionally, we identified a mitochondrial adenylate kinase (AK4) that regulates cellular ATP levels and AMPK signaling and whose expression significantly correlates with glioma patient survival. This study maps the bioenergetic landscape of >1,000 mitochondrial proteins in the context of varied metabolic substrates and begins to link key metabolic genes with clinical outcome.

Comments to be further addressed by JES Roselino

I will add some observations or at least one single observation.
Just at the beginning, when phosphorylation of proteins is presented, I assume you must mention that some proteins are activated by phosphorylation. This is fundamental in order to present self –organization reflex upon fast regulatory mechanisms. Even from an historical point of view. The first observation arrived from a sample due to be studied on the following day of glycogen synthetase. It was unintended left overnight out of the refrigerator. The result was it has changed from active form of the previous day to a non-active form. The story could have being finished here, if the researcher did not decide to spent this day increasing substrate levels (it could be a simple case of denaturation of proteins that changes its conformation despite the same order of amino acids). He kept on trying and found restoration of maximal activity. This assay was repeated with glycogen phosphorylase and the result was the opposite it increases its activity. This lead to the discovery of cAMP activated protein kinase and the assembly of a very complex system in the glycogen granule that is not a simple carbohydrate polymer. Instead it has several proteins assembled and preserves the capacity to receive from a single event (rise in cAMP) two opposing signals with maximal efficiency, stops glycogen synthesis, as long as levels of glucose 6 phosphate are low and increases glycogen phosphorylation as long as AMP levels are high).
I did everything I was able to do by the end of 1970 in order to repeat this assays with PK I, PKII and PKIII of M. Rouxii and Sutherland route to cAMP failed in this case. I ask Leloir to suggest to my chief (SP) the idea of AA, AB, BB subunits as was observed in lactic dehydrogenase (tetramer) indicating this as his idea. The reason was my “chief”(SP) more than once, have said it to me: “Leave these great ideas for the Houssay, Leloir etc…We must do our career with small things.” However, as she also have a faulty ability for recollection she also uses to arrive some time later, with the very same idea but in that case, as her idea.
Leloir, said to me: I will not offer your interpretation to her as mine. I think it is not phosphorylation, however I think it is glycosylation that explains the changes in the isoenzymes with the same molecular weight preserved. This dialogue explains why during “What is life” reading with him he asked me if from biochemist in exile, to biochemist I talked everything to him. Since I have considered that Schrödinger did not have confronted Darlington & Haldane for being in exile. Also, may explain why Leloir could have answered a bad telephone call from P. Boyer, Editor of The Enzymes in a way that suggest the the pattern could be of covalent changes over a protein. Our FEBS and Eur J. Biochemistry papers on pyruvate kinase of M. Rouxii is wrongly quoted in this way on his review about pyruvate kinase of that year(1971).

Another aspect I think you must call attention, in my opinion, is the following, show in detail with different colors what carbons belongs to CoA a huge molecule, in comparison with the single two carbons of acetate that will produce the enormous jump in energy yield in comparison with anaerobic glycolysis. The idea is how much must have being spent in DNA sequences to build that molecule in order to use only two atoms of carbon. Very limited aspects of biology could be explained in this way. In case we follow an alternative way of thinking, it becomes clearer that proteins were made more stable by interaction with other molecules (great and small). Afterwards, it rather easy to understand how the stability of protein-RNA complexes where transmitted to RNA (vibrational +solvational reactivity stability pair of conformational energy). Latter, millions of years, or as soon as, the information of interaction leading to activity and regulation could be found in RNA, proteins like reverse transcriptase move this information to a more stable form (DNA). In this way it is easier to understand the use of CoA to make two carbon molecules more reactive.

Yours,

JES Roselino

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Lipid Metabolism

Lipid Metabolism

Reporter and Curator: Larry H. Bernstein, MD, FCAP 

 

This is fourth of a series of articles, lipid metabolism, that began with signaling and signaling pathways. These discussion lay the groundwork to proceed in later discussions that will take on a somewhat different approach. These are critical to develop a more complete point of view of life processes.  I have indicated that many of the protein-protein interactions or protein-membrane interactions and associated regulatory features have been referred to previously, but the focus of the discussion or points made were different.  The role of lipids in circulating plasma proteins as biomarkers for coronary vascular disease can be traced to the early work of Frederickson and the classification of lipid disorders.  The very critical role of lipids in membrane structure in health and disease has had much less attention, despite the enormous importance, especially in the nervous system.

  1. Signaling and signaling pathways
  2. Signaling transduction tutorial.
  3. Carbohydrate metabolism

3.1  Selected References to Signaling and Metabolic Pathways in Leaders in Pharmaceutical Intelligence

  1. Lipid metabolism
  2. Protein synthesis and degradation
  3. Subcellular structure
  4. Impairments in pathological states: endocrine disorders; stress hypermetabolism; cancer.

 

Lipid Metabolism

http://www.elmhurst.edu/~chm/vchembook/622overview.html

Overview of Lipid Catabolism:

The major aspects of lipid metabolism are involved with

  • Fatty Acid Oxidationto produce energy or
  • the synthesis of lipids which is called Lipogenesis.

The metabolism of lipids and carbohydrates are related by the conversion of lipids from carbohydrates. This can be seen in the diagram. Notice the link through actyl-CoA, the seminal discovery of Fritz Lipmann. The metabolism of both is upset by diabetes mellitus, which results in the release of ketones (2/3 betahydroxybutyric acid) into the circulation.

 

metabolism of fats

metabolism of fats

 

http://www.elmhurst.edu/~chm/vchembook/images/590metabolism.gif

The first step in lipid metabolism is the hydrolysis of the lipid in the cytoplasm to produce glycerol and fatty acids.

Since glycerol is a three carbon alcohol, it is metabolized quite readily into an intermediate in glycolysis, dihydroxyacetone phosphate. The last reaction is readily reversible if glycerol is needed for the synthesis of a lipid.

The hydroxyacetone, obtained from glycerol is metabolized into one of two possible compounds. Dihydroxyacetone may be converted into pyruvic acid, a 3-C intermediate at the last step of glycolysis to make energy.

In addition, the dihydroxyacetone may also be used in gluconeogenesis (usually dependent on conversion of gluconeogenic amino acids) to make glucose-6-phosphate for glucose to the blood or glycogen depending upon what is required at that time.

Fatty acids are oxidized to acetyl CoA in the mitochondria using the fatty acid spiral. The acetyl CoA is then ultimately converted into ATP, CO2, and H2O using the citric acid cycle and the electron transport chain.

There are two major types of fatty acids – ω-3 and ω-6.  There are also saturated and unsaturated with respect to the existence of double bonds, and monounsaturated and polyunsatured.  Polyunsaturated fatty acids (PUFAs) are important in long term health, and it will be seen that high cardiovascular risk is most associated with a low ratio of ω-3/ω-6, the denominator being from animal fat. Ω-3 fatty acids are readily available from fish, seaweed, and flax seed. More can be said of this later.

Fatty acids are synthesized from carbohydrates and occasionally from proteins. Actually, the carbohydrates and proteins have first been catabolized into acetyl CoA. Depending upon the energy requirements, the acetyl CoA enters the citric acid cycle or is used to synthesize fatty acids in a process known as LIPOGENESIS.

The relationships between lipid and carbohydrate metabolism are
summarized in Figure 2.

 

fattyacidspiral

fattyacidspiral

http://www.elmhurst.edu/~chm/vchembook/images/620fattyacidspiral.gif

 

 Energy Production Fatty Acid Oxidation:

Visible” ATP:

In the fatty acid spiral, there is only one reaction which directly uses ATP and that is in the initiating step. So this is a loss of ATP and must be subtracted later.

A large amount of energy is released and restored as ATP during the oxidation of fatty acids. The ATP is formed from both the fatty acid spiral and the citric acid cycle.

 

Connections to Electron Transport and ATP:

One turn of the fatty acid spiral produces ATP from the interaction of the coenzymes FAD (step 1) and NAD+ (step 3) with the electron transport chain. Total ATP per turn of the fatty acid spiral is:

Electron Transport Diagram – (e.t.c.)

Step 1 – FAD into e.t.c. = 2 ATP
Step 3 – NAD+ into e.t.c. = 3 ATP
Total ATP per turn of spiral = 5 ATP

In order to calculate total ATP from the fatty acid spiral, you must calculate the number of turns that the spiral makes. Remember that the number of turns is found by subtracting one from the number of acetyl CoA produced. See the graphic on the left bottom.

Example with Palmitic Acid = 16 carbons = 8 acetyl groups

Number of turns of fatty acid spiral = 8-1 = 7 turns

ATP from fatty acid spiral = 7 turns and 5 per turn = 35 ATP.

This would be a good time to remember that single ATP that was needed to get the fatty acid spiral started. Therefore subtract it now.

NET ATP from Fatty Acid Spiral = 35 – 1 = 34 ATP

Review ATP Summary for Citric Acid Cycle:The acetyl CoA produced from the fatty acid spiral enters the citric acid cycle. When calculating ATP production, you have to show how many acetyl CoA are produced from a given fatty acid as this controls how many “turns” the citric acid cycle makes.Starting with acetyl CoA, how many ATP are made using the citric acid cycle? E.T.C = electron transport chain

 Step  ATP produced
7  1
Step 4 (NAD+ to E.T.C.) 3
Step 6 (NAD+ to E.T.C.)  3
Step10 (NAD+ to E.T.C.)  3
Step 8 (FAD to E.T.C.) 2
 NET 12 ATP

 

 

 ATP Summary for Palmitic Acid – Complete Metabolism:The phrase “complete metabolism” means do reactions until you end up with carbon dioxide and water. This also means to use fatty acid spiral, citric acid cycle, and electron transport as needed.Starting with palmitic acid (16 carbons) how many ATP are made using fatty acid spiral? This is a review of the above panel E.T.C = electron transport chain

 Step  ATP (used -) (produced +)
Step 1 (FAD to E.T.C.) +2
Step 4 (NAD+ to E.T.C.) +3
Total ATP  +5
 7 turns  7 x 5 = 35
initial step  -1
 NET  34 ATP

The fatty acid spiral ends with the production of 8 acetyl CoA from the 16 carbon palmitic acid.

Starting with one acetyl CoA, how many ATP are made using the citric acid cycle? Above panel gave the answer of 12 ATP per acetyl CoA.

E.T.C = electron transport chain

 Step  ATP produced
One acetyl CoA per turn C.A.C. +12 ATP
8 Acetyl CoA = 8 turns C.A.C. 8 x 12 = 96 ATP
Fatty Acid Spiral 34 ATP
GRAND TOTAL  130 ATP

 

Fyodor Lynen

Feodor Lynen was born in Munich on 6 April 1911, the son of Wilhelm Lynen, Professor of Mechanical Engineering at the Munich Technische Hochschule. He received his Doctorate in Chemistry from Munich University under Heinrich Wieland, who had won the Nobel Prize for Chemistry in 1927, in March 1937 with the work: «On the Toxic Substances in Amanita». in 1954 he became head of the Max-Planck-Institut für Zellchemie, newly created for him as a result of the initiative of Otto Warburg and Otto Hahn, then President of the Max-Planck-Gesellschaft zur Förderung der Wissenschaften.

Lynen’s work was devoted to the elucidation of the chemical details of metabolic processes in living cells, and of the mechanisms of metabolic regulation. The problems tackled by him, in conjunction with German and other workers, include the Pasteur effect, acetic acid degradation in yeast, the chemical structure of «activated acetic acid» of «activated isoprene», of «activated carboxylic acid», and of cytohaemin, degradation of fatty acids and formation of acetoacetic acid, degradation of tararic acid, biosynthesis of cysteine, of terpenes, of rubber, and of fatty acids.

In 1954 Lynen received the Neuberg Medal of the American Society of European Chemists and Pharmacists, in 1955 the Liebig Commemorative Medal of the Gesellschaft Deutscher Chemiker, in 1961 the Carus Medal of the Deutsche Akademie der Naturforscher «Leopoldina», and in 1963 the Otto Warburg Medal of the Gesellschaft für Physiologische Chemie. He was also a member of the U>S> National Academy of Sciences, and shared the Nobel Prize in Physiology and Medicine with Konrad Bloch in 1964, and was made President of the Gesellschaft Deutscher Chemiker (GDCh) in 1972.

This biography was written at the time of the award and first published in the book series Les Prix Nobel. It was later edited and republished in Nobel Lectures, and shortened by myself.

The Pathway from “Activated Acetic Acid” to the Terpenes and Fatty Acids

My first contact with dynamic biochemistry in 1937 occurred at an exceedingly propitious time. The remarkable investigations on the enzyme chain of respiration, on the oxygen-transferring haemin enzyme of respiration, the cytochromes, the yellow enzymes, and the pyridine proteins had thrown the first rays of light on the chemical processes underlying the mystery of biological catalysis, which had been recognised by your famous countryman Jöns Jakob Berzelius. Vitamin B2 , which is essential to the nourishment of man and of animals, had been recognised by Hugo Theorell in the form of the phosphate ester as the active group of an important class of enzymes, and the fermentation processes that are necessary for Pasteur’s “life without oxygen”

had been elucidated as the result of a sequence of reactions centered around “hydrogen shift” and “phosphate shift” with adenosine triphosphate as the phosphate-transferring coenzyme. However, 1,3-diphosphoglyceric acid, the key substance to an understanding of the chemical relation between oxidation and phosphorylation, still lay in the depths of the unknown. Never-

theless, Otto Warburg was on its trail in the course of his investigations on the fermentation enzymes, and he was able to present it to the world in 1939.

 

This was the period in which I carried out my first independent investigation, which was concerned with the metabolism of yeast cells after freezing in liquid air, and which brought me directly into contact with the mechanism of alcoholic fermentation. This work taught me a great deal, and yielded two important pieces of information.

 

  • The first was that in experiments with living cells, special attention must be given to the permeability properties of the cell membranes, and
  • the second was that the adenosine polyphosphate system plays a vital part in the cell,
    • not only in energy transfer, but
    • also in the regulation of the metabolic processes.

 

.

This investigation aroused by interest in problems of metabolic regulation, which led me to the investigation of the Pasteur effects, and has remained with me to the present day.

 

My subsequent concern with the problem of the acetic acid metabolism arose from my stay at Heinrich Wieland’s laboratory. Workers here had studied the oxidation of acetic acid by yeast cells, and had found that though most of the acetic acid undergoes complete oxidation, some remains in the form of succinic and citric acids.

 

The explanation of these observations was provided-by the Thunberg-Wieland process, according to which two molecules of acetic acid are dehydrogenated to succinic acid, which is converted back into acetic acid via oxaloacetic acid, pyruvic acid, and acetaldehyde, or combines at the oxaloacetic acid stage with a further molecule of acetic acid to form citric acid (Fig. 1). However, an experimental check on this view by a Wieland’s student Robert Sonderhoffs brought a surprise. The citric acid formed when trideuteroacetic acid was supplied to yeast cells contained the expected quantity of deuterium, but the succinic acid contained only half of the four deuterium atoms required by Wieland’s scheme.

 

This investigation aroused by interest in problems of metabolic regulation, which led me to the investigation of the Pasteur effects, and has remained with me to the present day. My subsequent concern with the problem of the acetic acid metabolism arose from my stay at Heinrich Wieland’s laboratory. Workers here had studied the oxidation of acetic acid by yeast cells, and had found that though most of the acetic acid undergoes complete oxidation, some remains in the form of succinic and citric acid

The answer provided by Martius was that citric acid  is in equilibrium with isocitric acid and is oxidised to cr-ketoglutaric acid, the conversion of which into succinic acid had already been discovered by Carl Neuberg (Fig. 1).

It was possible to assume with fair certainty from these results that the succinic acid produced by yeast from acetate is formed via citric acid. Sonderhoff’s experiments with deuterated acetic acid led to another important discovery.

In the analysis of the yeast cells themselves, it was found that while the carbohydrate fraction contained only insignificant quantities of deuterium, large quantities of heavy hydrogen were present in the fatty acids formed and in the sterol fraction. This showed that

  • fatty acids and sterols were formed directly from acetic acid, and not indirectly via the carbohydrates.

As a result of Sonderhoff’s early death, these important findings were not pursued further in the Munich laboratory.

  • This situation was elucidated only by Konrad Bloch’s isotope experiments, on which he reports.

My interest first turned entirely to the conversion of acetic acid into citric acid, which had been made the focus of the aerobic degradation of carbohydrates by the formulation of the citric acid cycle by Hans Adolf Krebs. Unlike Krebs, who regarded pyruvic acid as the condensation partner of acetic acid,

  • we were firmly convinced, on the basis of the experiments on yeast, that pyruvic acid is first oxidised to acetic acid, and only then does the condensation take place.

Further progress resulted from Wieland’s observation that yeast cells that had been “impoverished” in endogenous fuels by shaking under oxygen were able to oxidise added acetic acid only after a certain “induction period” (Fig. 2). This “induction period” could be shortened by addition of small quantities of a readily oxidisable substrate such as ethyl alcohol, though propyl and butyl alcohol were also effective. I explained this by assuming that acetic acid is converted, at the expense of the oxidation of the alcohol, into an “activated acetic acid”, and can only then condense with oxalacetic acid.

In retrospect, we find that I had come independently on the same group of problems as Fritz Lipmann, who had discovered that inorganic phosphate is indispensable to the oxidation of pyruvic acid by lactobacilli, and had detected acetylphosphate as an oxidation product. Since this anhydride of acetic acid and phosphoric acid could be assumed to be the “activated acetic acid”.

I learned of the advances that had been made in the meantime in the investigation of the problem of “activated acetic acid”. Fritz Lipmann has described the development at length in his Nobel Lecture’s, and I need not repeat it. The main advance was the recognition that the formation of “activated acetic acid” from acetate involved not only ATP as an energy source, but also the newly discovered coenzyme A, which contains the vitamin pantothenic acid, and that “activated acetic acid” was probably an acetylated coenzyme  A.

http://www.nobelprize.org/nobel_prizes/medicine/laureates/1964/lynen-bio.html

http://onlinelibrary.wiley.com/store/10.1002/anie.201106003/asset/image_m/mcontent.gif?v=1&s=1e6dc789dfa585fe48947e92cc5dfdcabd8e2677

Fyodor Lynen

Lynen’s most important research at the University of Munich focused on intermediary metabolism, cholesterol synthesis, and fatty acid biosynthesis. Metabolism involves all the chemical processes by which an organism converts matter and energy into forms that it can use. Metabolism supplies the matter—the molecular building blocks an organism needs for the growth of new tissues. These building blocks must either come from the breakdown of molecules of food, such as glucose (sugar) and fat, or be built up from simpler molecules within the organism.

Cholesterol is one of the fatty substances found in animal tissues. The human body produces cholesterol, but this substance also enters the body in food. Meats, egg yolks, and milk products, such as butter and cheese, contain cholesterol. Such organs as the brain and liver contain much cholesterol. Cholesterol is a type of lipid, one of the classes of chemical compounds essential to human health. It makes up an important part of the membranes of each cell in the body. The body also uses cholesterol to produce vitamin D and certain hormones.

All fats are composed of an alcohol called glycerol and substances called fatty acids. A fatty acid consists of a long chain of carbon atoms, to which hydrogen atoms are attached. There are three types of fatty acids: saturated, monounsaturated, and polyunsaturated.

Living cells manufacture complicated chemical compounds from simpler substances through a process called biosynthesis. For example, simple molecules called amino acids are put together to make proteins. The biosynthesis of both fatty acids and cholesterol begins with a chemically active form of acetate, a two-carbon molecule. Lynen discovered that the active form of acetate is a coenzyme, a heat-stabilized, water-soluble portion of an enzyme, called acetyl coenzyme A. Lynen and his colleagues demonstrated that the formation of cholesterol begins with the condensation of two molecules of acetyl coenzyme A to form acetoacetyl coenzyme A, a four-carbon molecule.

http://science.howstuffworks.com/dictionary/famous-scientists/biologists/feodor-lynen-info.htm

Fyodor Lynen

Fyodor Lynen

 

SREBPs: activators of the complete program of cholesterol and fatty acid synthesis in the liver

Jay D. Horton1,2, Joseph L. Goldstein1 and Michael S. Brown1

1Department of Molecular Genetics, and
2Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA

J Clin Invest. 2002;109(9):1125–1131.
http://dx.doi.org:/10.1172/JCI15593
Lipid homeostasis in vertebrate cells is regulated by a family of membrane-bound transcription factors designated sterol regulatory element–binding proteins (SREBPs). SREBPs directly activate the expression of more than 30 genes dedicated to the synthesis and uptake of cholesterol, fatty acids, triglycerides, and phospholipids, as well as the NADPH cofactor required to synthesize these molecules (14). In the liver, three SREBPs regulate the production of lipids for export into the plasma as lipoproteins and into the bile as micelles. The complex, interdigitated roles of these three SREBPs have been dissected through the study of ten different lines of gene-manipulated mice. These studies form the subject of this review.

SREBPs: activation through proteolytic processing

SREBPs belong to the basic helix-loop-helix–leucine zipper (bHLH-Zip) family of transcription factors, but they differ from other bHLH-Zip proteins in that they are synthesized as inactive precursors bound to the endoplasmic reticulum (ER) (1, 5). Each SREBP precursor of about 1150 amino acids is organized into three domains: (a) an NH2-terminal domain of about 480 amino acids that contains the bHLH-Zip region for binding DNA; (b) two hydrophobic transmembrane–spanning segments interrupted by a short loop of about 30 amino acids that projects into the lumen of the ER; and (c) a COOH-terminal domain of about 590 amino acids that performs the essential regulatory function described below.

In order to reach the nucleus and act as a transcription factor, the NH2-terminal domain of each SREBP must be released from the membrane proteolytically (Figure 1). Three proteins required for SREBP processing have been delineated in cultured cells, using the tools of somatic cell genetics (see ref. 5for review). One is an escort protein designated SREBP cleavage–activating protein (SCAP). The other two are proteases, designated Site-1 protease (S1P) and Site-2 protease (S2P). Newly synthesized SREBP is inserted into the membranes of the ER, where its COOH-terminal regulatory domain binds to the COOH-terminal domain of SCAP (Figure 1).

 

Figure 1

Model for the sterol-mediated proteolytic release of SREBPs from membranes JCI0215593.f1

Model for the sterol-mediated proteolytic release of SREBPs from membranes JCI0215593.f1

 

Model for the sterol-mediated proteolytic release of SREBPs from membranes. SCAP is a sensor of sterols and an escort of SREBPs. When cells are depleted of sterols, SCAP transports SREBPs from the ER to the Golgi apparatus, where two proteases, Site-1 protease (S1P) and Site-2 protease (S2P), act sequentially to release the NH2-terminal bHLH-Zip domain from the membrane. The bHLH-Zip domain enters the nucleus and binds to a sterol response element (SRE) in the enhancer/promoter region of target genes, activating their transcription. When cellular cholesterol rises, the SCAP/SREBP complex is no longer incorporated into ER transport vesicles, SREBPs no longer reach the Golgi apparatus, and the bHLH-Zip domain cannot be released from the membrane. As a result, transcription of all target genes declines. Reprinted from ref. 5 with permission.

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SCAP is both an escort for SREBPs and a sensor of sterols. When cells become depleted in cholesterol, SCAP escorts the SREBP from the ER to the Golgi apparatus, where the two proteases reside. In the Golgi apparatus, S1P, a membrane-bound serine protease, cleaves the SREBP in the luminal loop between its two membrane-spanning segments, dividing the SREBP molecule in half (Figure 1). The NH2-terminal bHLH-Zip domain is then released from the membrane via a second cleavage mediated by S2P, a membrane-bound zinc metalloproteinase. The NH2-terminal domain, designated nuclear SREBP (nSREBP), translocates to the nucleus, where it activates transcription by binding to nonpalindromic sterol response elements (SREs) in the promoter/enhancer regions of multiple target genes.

 

Figure 1

 

When the cholesterol content of cells rises, SCAP senses the excess cholesterol through its membranous sterol-sensing domain, changing its conformation in such a way that the SCAP/SREBP complex is no longer incorporated into ER transport vesicles. The net result is that SREBPs lose their access to S1P and S2P in the Golgi apparatus, so their bHLH-Zip domains cannot be released from the ER membrane, and the transcription of target genes ceases (1, 5). The biophysical mechanism by which SCAP senses sterol levels in the ER membrane and regulates its movement to the Golgi apparatus is not yet understood. Elucidating this mechanism will be fundamental to understanding the molecular basis of cholesterol feedback inhibition of gene expression.

SREBPs: two genes, three proteins

The mammalian genome encodes three SREBP isoforms, designated SREBP-1a, SREBP-1c, and SREBP-2. SREBP-2 is encoded by a gene on human chromosome 22q13. Both SREBP-1a and -1c are derived from a single gene on human chromosome 17p11.2 through the use of alternative transcription start sites that produce alternate forms of exon 1, designated 1a and 1c (1). SREBP-1a is a potent activator of all SREBP-responsive genes, including those that mediate the synthesis of cholesterol, fatty acids, and triglycerides. High-level transcriptional activation is dependent on exon 1a, which encodes a longer acidic transactivation segment than does the first exon of SREBP-1c. The roles of SREBP-1c and SREBP-2 are more restricted than that of SREBP-1a. SREBP-1c preferentially enhances transcription of genes required for fatty acid synthesis but not cholesterol synthesis. Like SREBP-1a, SREBP-2 has a long transcriptional activation domain, but it preferentially activates cholesterol synthesis (1). SREBP-1a and SREBP-2 are the predominant isoforms of SREBP in most cultured cell lines, whereas SREBP-1c and SREBP-2 predominate in the liver and most other intact tissues (6).

When expressed at higher than physiologic levels, each of the three SREBP isoforms can activate all enzymes indicated in Figure 2, which shows the biosynthetic pathways used to generate cholesterol and fatty acids. However, at normal levels of expression, SREBP-1c favors the fatty acid biosynthetic pathway and SREBP-2 favors cholesterologenesis. SREBP-2–responsive genes in the cholesterol biosynthetic pathway include those for the enzymes HMG-CoA synthase, HMG-CoA reductase, farnesyl diphosphate synthase, and squalene synthase. SREBP-1c–responsive genes include those for ATP citrate lyase (which produces acetyl-CoA) and acetyl-CoA carboxylase and fatty acid synthase (which together produce palmitate [C16:0]). Other SREBP-1c target genes encode a rate-limiting enzyme of the fatty acid elongase complex, which converts palmitate to stearate (C18:0) (ref.7); stearoyl-CoA desaturase, which converts stearate to oleate (C18:1); and glycerol-3-phosphate acyltransferase, the first committed enzyme in triglyceride and phospholipid synthesis (3). Finally, SREBP-1c and SREBP-2 activate three genes required to generate NADPH, which is consumed at multiple stages in these lipid biosynthetic pathways (8) (Figure 2).

 

Figure 2

 

major metabolic intermediates in the pathways for synthesis of cholesterol, fatty acids, and triglycerides JCI0215593.f2

major metabolic intermediates in the pathways for synthesis of cholesterol, fatty acids, and triglycerides JCI0215593.f2

 

 

 

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Genes regulated by SREBPs. The diagram shows the major metabolic intermediates in the pathways for synthesis of cholesterol, fatty acids, and triglycerides. In vivo, SREBP-2 preferentially activates genes of cholesterol metabolism, whereas SREBP-1c preferentially activates genes of fatty acid and triglyceride metabolism. DHCR, 7-dehydrocholesterol reductase; FPP, farnesyl diphosphate; GPP, geranylgeranyl pyrophosphate synthase; CYP51, lanosterol 14α-demethylase; G6PD, glucose-6-phosphate dehydrogenase; PGDH, 6-phosphogluconate dehydrogenase; GPAT, glycerol-3-phosphate acyltransferase.

Genes regulated by SREBPs. The diagram shows the major metabolic intermediates in the pathways for synthesis of cholesterol, fatty acids, and triglycerides. In vivo, SREBP-2 preferentially activates genes of cholesterol metabolism, whereas SREBP-1c preferentially activates genes of fatty acid and triglyceride metabolism. DHCR, 7-dehydrocholesterol reductase; FPP, farnesyl diphosphate; GPP, geranylgeranyl pyrophosphate synthase; CYP51, lanosterol 14α-demethylase; G6PD, glucose-6-phosphate dehydrogenase; PGDH, 6-phosphogluconate dehydrogenase; GPAT, glycerol-3-phosphate acyltransferase.

Knockout and transgenic mice

Ten different genetically manipulated mouse models that either lack or overexpress a single component of the SREBP pathway have been generated in the last 6 years (916). The key molecular and metabolic alterations observed in these mice are summarized in Table 1.

 

Table 1
Alterations in hepatic lipid metabolism in gene-manipulated mice overexpressing or lacking SREBPs

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Knockout mice that lack all nSREBPs die early in embryonic development. For instance, a germline deletion of S1p, which prevents the processing of all SREBP isoforms, results in death before day 4 of development (15, 17). Germline deletion of Srebp2 leads to 100% lethality at a later stage of embryonic development than does deletion of S1p (embryonic day 7–8). In contrast, germline deletion of Srebp1, which eliminates both the 1a and the 1c transcripts, leads to partial lethality, in that about 15–45% of Srebp1–/– mice survive (13). The surviving homozygotes manifest elevated levels of SREBP-2 mRNA and protein (Table 1), which presumably compensates for the loss of SREBP-1a and -1c. When the SREBP-1c transcript is selectively eliminated, no embryonic lethality is observed, suggesting that the partial embryonic lethality in the Srebp1–/– mice is due to the loss of the SREBP-1a transcript (16).

To bypass embryonic lethality, we have produced mice in which all SREBP function can be disrupted in adulthood through induction of Cre recombinase. For this purpose, loxP recombination sites were inserted into genomic regions that flank crucial exons in the Scap or S1p genes (so-called floxed alleles) (14, 15). Mice homozygous for the floxed gene and heterozygous for a Cre recombinase transgene, which is under control of an IFN-inducible promoter (MX1-Cre), can be induced to delete Scap or S1p by stimulating IFN expression. Thus, following injection with polyinosinic acid–polycytidylic acid, a double-stranded RNA that provokes antiviral responses, the Cre recombinase is produced in liver and disrupts the floxed gene by recombination between the loxP sites.

Cre-mediated disruption of Scap or S1p dramatically reduces nSREBP-1 and nSREBP-2 levels in liver and diminishes expression of all SREBP target genes in both the cholesterol and the fatty acid synthetic pathways (Table 1). As a result, the rates of synthesis of cholesterol and fatty acids fall by 70–80% in Scap- and S1p-deficient livers.

In cultured cells, the processing of SREBP is inhibited by sterols, and the sensor for this inhibition is SCAP (5). To learn whether SCAP performs the same function in liver, we have produced transgenic mice that express a mutant SCAP with a single amino acid substitution in the sterol-sensing domain (D443N) (12). Studies in tissue culture show that SCAP(D443N) is resistant to inhibition by sterols. Cells that express a single copy of this mutant gene overproduce cholesterol (18). Transgenic mice that express this mutant version of SCAP in the liver exhibit a similar phenotype (12). These livers manifest elevated levels of nSREBP-1 and nSREBP-2, owing to constitutive SREBP processing, which is not suppressed when the animals are fed a cholesterol-rich diet. nSREBP-1 and -2 increase the expression of all SREBP target genes shown in Figure 2, thus stimulating cholesterol and fatty acid synthesis and causing a marked accumulation of hepatic cholesterol and triglycerides (Table 1). This transgenic model provides strong in vivo evidence that SCAP activity is normally under partial inhibition by endogenous sterols, which keeps the synthesis of cholesterol and fatty acids in a partially repressed state in the liver.

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Function of individual SREBP isoforms in vivo

To study the functions of individual SREBPs in the liver, we have produced transgenic mice that overexpress truncated versions of SREBPs (nSREBPs) that terminate prior to the membrane attachment domain. These nSREBPs enter the nucleus directly, bypassing the sterol-regulated cleavage step. By studying each nSREBP isoform separately, we could determine their distinct activating properties, albeit when overexpressed at nonphysiologic levels.

Overexpression of nSREBP-1c in the liver of transgenic mice produces a triglyceride-enriched fatty liver with no increase in cholesterol (10). mRNAs for fatty acid synthetic enzymes and rates of fatty acid synthesis are elevated fourfold in this tissue, whereas the mRNAs for cholesterol synthetic enzymes and the rate of cholesterol synthesis are not increased (8). Conversely, overexpression of nSREBP-2 in the liver increases the mRNAs only fourfold. This increase in cholesterol synthesis is even more remarkable when encoding all cholesterol biosynthetic enzymes; the most dramatic is a 75-fold increase in HMG-CoA reductase mRNA (11). mRNAs for fatty acid synthesis enzymes are increased to a lesser extent, consistent with the in vivo observation that the rate of cholesterol synthesis increases 28-fold in these transgenic nSREBP-2 livers, while fatty acid synthesis increases one considers the extent of cholesterol overload in this tissue, which would ordinarily reduce SREBP processing and essentially abolish cholesterol synthesis (Table 1).

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We have also studied the consequences of overexpressing SREBP-1a, which is expressed only at low levels in the livers of adult mice, rats, hamsters, and humans (6). nSREBP-1a transgenic mice develop a massive fatty liver engorged with both cholesterol and triglycerides (9), with heightened expression of genes controlling cholesterol biosynthesis and, still more dramatically, fatty acid synthesis (Table 1). The preferential activation of fatty acid synthesis (26-fold increase) relative to cholesterol synthesis (fivefold increase) explains the greater accumulation of triglycerides in their livers. The relative representation of the various fatty acids accumulating in this tissue is also unusual. Transgenic nSREBP-1a livers contain about 65% oleate (C18:1), markedly higher levels than the 15–20% found in typical wild-type livers (8) — a result of the induction of fatty acid elongase and stearoyl-CoA desaturase-1 (7). Considered together, the overexpression studies indicate that both SREBP-1 isoforms show a relative preference for activating fatty acid synthesis, whereas SREBP-2 favors cholesterol.

The phenotype of animals lacking the Srebp1 gene, which encodes both the SREBP-1a and -1c transcripts, also supports the notion of distinct hepatic functions for SREBP-1 and SREBP-2 (13). Most homozygous SREBP-1 knockout mice die in utero. The surviving Srebp1–/– mice show reduced synthesis of fatty acids, owing to reduced expression of mRNAs for fatty acid synthetic enzymes (Table 1). Hepatic nSREBP-2 levels increase in these mice, presumably in compensation for the loss of nSREBP-1. As a result, transcription of cholesterol biosynthetic genes increases, producing a threefold increase in hepatic cholesterol synthesis (Table 1).

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The studies in genetically manipulated mice clearly show that, as in cultured cells, SCAP and S1P are required for normal SREBP processing in the liver. SCAP, acting through its sterol-sensing domain, mediates feedback regulation of cholesterol synthesis. The SREBPs play related but distinct roles: SREBP-1c, the predominant SREBP-1 isoform in adult liver, preferentially activates genes required for fatty acid synthesis, while SREBP-2 preferentially activates the LDL receptor gene and various genes required for cholesterol synthesis. SREBP-1a and SREBP-2, but not SREBP-1c, are required for normal embryogenesis.

Transcriptional regulation of SREBP genes

Regulation of SREBPs occurs at two levels — transcriptional and posttranscriptional. The posttranscriptional regulation discussed above involves the sterol-mediated suppression of SREBP cleavage, which results from sterol-mediated suppression of the movement of the SCAP/SREBP complex from the ER to the Golgi apparatus (Figure 1). This form of regulation is manifest not only in cultured cells (1), but also in the livers of rodents fed cholesterol-enriched diets (19).

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The transcriptional regulation of the SREBPs is more complex. SREBP-1c and SREBP-2 are subject to distinct forms of transcriptional regulation, whereas SREBP-1a appears to be constitutively expressed at low levels in liver and most other tissues of adult animals (6). One mechanism of regulation shared by SREBP-1c and SREBP-2 involves a feed-forward regulation mediated by SREs present in the enhancer/promoters of each gene (20, 21). Through this feed-forward loop, nSREBPs activate the transcription of their own genes. In contrast, when nSREBPs decline, as in Scap or S1p knockout mice, there is a secondary decline in the mRNAs encoding SREBP-1c and SREBP-2 (14, 15).

Three factors selectively regulate the transcription of SREBP-1c: liver X-activated receptors (LXRs), insulin, and glucagon. LXRα and LXRβ, nuclear receptors that form heterodimers with retinoid X receptors, are activated by a variety of sterols, including oxysterol intermediates that form during cholesterol biosynthesis (2224). An LXR-binding site in the SREBP-1c promoter activates SREBP-1c transcription in the presence of LXR agonists (23). The functional significance of LXR-mediated SREBP-1c regulation has been confirmed in two animal models. Mice that lack both LXRα and LXRβ express reduced levels of SREBP-1c and its lipogenic target enzymes in liver and respond relatively weakly to treatment with a synthetic LXR agonist (23). Because a similar blunted response is found in mice that lack SREBP-1c, it appears that LXR increases fatty acid synthesis largely by inducing SREBP-1c (16). LXR-mediated activation of SREBP-1c transcription provides a mechanism for the cell to induce the synthesis of oleate when sterols are in excess (23). Oleate is the preferred fatty acid for the synthesis of cholesteryl esters, which are necessary for both the transport and the storage of cholesterol.

LXR-mediated regulation of SREBP-1c appears also to be one mechanism by which unsaturated fatty acids suppress SREBP-1c transcription and thus fatty acid synthesis. Rodents fed diets enriched in polyunsaturated fatty acids manifest reduced SREBP-1c mRNA expression and low rates of lipogenesis in liver (25). In vitro, unsaturated fatty acids competitively block LXR activation of SREBP-1c expression by antagonizing the activation of LXR by its endogenous ligands (26). In addition to LXR-mediated transcriptional inhibition, polyunsaturated fatty acids lower SREBP-1c levels by accelerating degradation of its mRNA (27). These combined effects may contribute to the long-recognized ability of polyunsaturated fatty acids to lower plasma triglyceride levels.

SREBP-1c and the insulin/glucagon ratio

The liver is the organ responsible for the conversion of excess carbohydrates to fatty acids to be stored as triglycerides or burned in muscle. A classic action of insulin is to stimulate fatty acid synthesis in liver during times of carbohydrate excess. The action of insulin is opposed by glucagon, which acts by raising cAMP. Multiple lines of evidence suggest that insulin’s stimulatory effect on fatty acid synthesis is mediated by an increase in SREBP-1c. In isolated rat hepatocytes, insulin treatment increases the amount of mRNA for SREBP-1c in parallel with the mRNAs of its target genes (28, 29). The induction of the target genes can be blocked if a dominant negative form of SREBP-1c is expressed (30). Conversely, incubating primary hepatocytes with glucagon or dibutyryl cAMP decreases the mRNAs for SREBP-1c and its associated lipogenic target genes (30, 31).

In vivo, the total amount of SREBP-1c in liver and adipose tissue is reduced by fasting, which suppresses insulin and increases glucagon levels, and is elevated by refeeding (32, 33). The levels of mRNA for SREBP-1c target genes parallel the changes in SREBP-1c expression. Similarly, SREBP-1c mRNA levels fall when rats are treated with streptozotocin, which abolishes insulin secretion, and rise after insulin injection (29). Overexpression of nSREBP-1c in livers of transgenic mice prevents the reduction in lipogenic mRNAs that normally follows a fall in plasma insulin levels (32). Conversely, in livers of Scap knockout mice that lack all nSREBPs in the liver (14) or knockout mice lacking either nSREBP-1c (16) or both SREBP-1 isoforms (34), there is a marked decrease in the insulin-induced stimulation of lipogenic gene expression that normally occurs after fasting/refeeding. It should be noted that insulin and glucagon also exert a posttranslational control of fatty acid synthesis though changes in the phosphorylation and activation of acetyl-CoA carboxylase. The posttranslational regulation of fatty acid synthesis persists in transgenic mice that overexpress nSREBP-1c (10). In these mice, the rates of fatty acid synthesis, as measured by [3H]water incorporation, decline after fasting even though the levels of the lipogenic mRNAs remain high (our unpublished observations).

Taken together, the above evidence suggests that SREBP-1c mediates insulin’s lipogenic actions in liver. Recent in vitro and in vivo studies involving adenoviral gene transfer suggest that SREBP-1c may also contribute to the regulation of glucose uptake and glucose synthesis. When overexpressed in hepatocytes, nSREBP-1c induces expression of glucokinase, a key enzyme in glucose utilization. It also suppresses phosphoenolpyruvate carboxykinase, a key gluconeogenic enzyme (35, 36).

SREBPs in disease

Many individuals with obesity and insulin resistance also have fatty livers, one of the most commonly encountered liver abnormalities in the US (37). A subset of individuals with fatty liver go on to develop fibrosis, cirrhosis, and liver failure. Evidence indicates that the fatty liver of insulin resistance is caused by SREBP-1c, which is elevated in response to the high insulin levels. Thus, SREBP-1c levels are elevated in the fatty livers of obese (ob/ob) mice with insulin resistance and hyperinsulinemia caused by leptin deficiency (38, 39). Despite the presence of insulin resistance in peripheral tissues, insulin continues to activate SREBP-1c transcription and cleavage in the livers of these insulin-resistant mice. The elevated nSREBP-1c increases lipogenic gene expression, enhances fatty acid synthesis, and accelerates triglyceride accumulation (31, 39). These metabolic abnormalities are reversed with the administration of leptin, which corrects the insulin resistance and lowers the insulin levels (38).

Metformin, a biguanide drug used to treat insulin-resistant diabetes, reduces hepatic nSREBP-1 levels and dramatically lowers the lipid accumulation in livers of insulin-resistant ob/ob mice (40). Metformin stimulates AMP-activated protein kinase (AMPK), an enzyme that inhibits lipid synthesis through phosphorylation and inactivation of key lipogenic enzymes (41). In rat hepatocytes, metformin-induced activation of AMPK also leads to decreased mRNA expression of SREBP-1c and its lipogenic target genes (41), but the basis of this effect is not understood.

The incidence of coronary artery disease increases with increasing plasma LDL-cholesterol levels, which in turn are inversely proportional to the levels of hepatic LDL receptors. SREBPs stimulate LDL receptor expression, but they also enhance lipid synthesis (1), so their net effect on plasma lipoprotein levels depends on a balance between opposing effects. In mice, the plasma levels of lipoproteins tend to fall when SREBPs are either overexpressed or underexpressed. In transgenic mice that overexpress nSREBPs in liver, plasma cholesterol and triglycerides are generally lower than in control mice (Table 1), even though these mice massively overproduce fatty acids, cholesterol, or both. Hepatocytes of nSREBP-1a transgenic mice overproduce VLDL, but these particles are rapidly removed through the action of LDL receptors, and they do not accumulate in the plasma. Indeed, some nascent VLDL particles are degraded even before secretion by a process that is mediated by LDL receptors (42). The high levels of nSREBP-1a in these animals support continued expression of the LDL receptor, even in cells whose cholesterol concentration is elevated. In LDL receptor–deficient mice carrying the nSREBP-1a transgene, plasma cholesterol and triglyceride levels rise tenfold (43).

Mice that lack all SREBPs in liver as a result of disruption of Scap or S1p also manifest lower plasma cholesterol and triglyceride levels (Table 1).

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In these mice, hepatic cholesterol and triglyceride synthesis is markedly reduced, and this likely causes a decrease in VLDL production and secretion. LDL receptor mRNA and LDL clearance from plasma is also significantly reduced in these mice, but the reduction in LDL clearance is less than the overall reduction in VLDL secretion, the net result being a decrease in plasma lipid levels (15). However, because

humans and mice differ substantially with regard to LDL receptor expression, LDL levels, and other aspects of lipoprotein metabolism,

it is difficult to predict whether human plasma lipids will rise or fall when the SREBP pathway is blocked or activated.

SREBPs in liver: unanswered questions

The studies of SREBPs in liver have exposed a complex regulatory system whose individual parts are coming into focus. Major unanswered questions relate to the ways in which the transcriptional and posttranscriptional controls on SREBP activity are integrated so as to permit independent regulation of cholesterol and fatty acid synthesis in specific nutritional states. A few clues regarding these integration mechanisms are discussed below.

Whereas cholesterol synthesis depends almost entirely on SREBPs, fatty acid synthesis is only partially dependent on these proteins. This has been shown most clearly in cultured nonhepatic cells such as Chinese hamster ovary cells. In the absence of SREBP processing, as when the Site-2 protease is defective, the levels of mRNAs encoding cholesterol biosynthetic enzymes and the rates of cholesterol synthesis decline nearly to undetectable levels, whereas the rate of fatty acid synthesis is reduced by only 30% (44). Under these conditions, transcription of the fatty acid biosynthetic genes must be maintained by factors other than SREBPs. In liver, the gene encoding fatty acid synthase (FASN) can be activated transcriptionally by upstream stimulatory factor, which acts in concert with SREBPs (45). The FASN promoter also contains an LXR element that permits a low-level response to LXR ligands even when SREBPs are suppressed (46). These two transcription factors may help to maintain fatty acid synthesis in liver when nSREBP-1c is low.

Another mechanism of differential regulation is seen in the ability of cholesterol to block the processing of SREBP-2, but not SREBP-1, under certain metabolic conditions. This differential regulation has been studied most thoroughly in cultured cells such as human embryonic kidney (HEK-293) cells. When these cells are incubated in the absence of fatty acids and cholesterol, the addition of sterols blocks processing of SREBP-2, but not SREBP-1, which is largely produced as SREBP-1a in these cells (47). Inhibition of SREBP-1 processing requires an unsaturated fatty acid, such as oleate or arachidonate, in addition to sterols (47). In the absence of fatty acids and in the presence of sterols, SCAP may be able to carry SREBP-1 proteins, but not SREBP-2, to the Golgi apparatus. Further studies are necessary to document this apparent independent regulation of SREBP-1 and SREBP-2 processing and to determine its mechanism.

 

Acknowledgments

Support for the research cited from the authors’ laboratories was provided by grants from the NIH (HL-20948), the Moss Heart Foundation, the Keck Foundation, and the Perot Family Foundation. J.D. Horton is a Pew Scholar in the Biomedical Sciences and is the recipient of an Established Investigator Grant from the American Heart Association and a Research Scholar Award from the American Digestive Health Industry.

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  1. Sakakura, Y, et al. Sterol regulatory element-binding proteins induce an entire pathway of cholesterol synthesis. Biochem Biophys Res Commun 2001. 286:176-183.

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  1. Goldstein, JL, Rawson, RB, Brown, MS. Mutant mammalian cells as tools to delineate the sterol regulatory element-binding protein pathway for feedback regulation of lipid synthesis. Arch Biochem Biophys 2002. 397:139-148.

View this article via: PubMed

  1. Shimomura, I, Shimano, H, Horton, JD, Goldstein, JL, Brown, MS. Differential expression of exons 1a and 1c in mRNAs for sterol regulatory element binding protein-1 in human and mouse organs and cultured cells. J Clin Invest 1997. 99:838-845.

View this article via: JCI.org PubMed

  1. Moon, Y-A, Shah, NA, Mohapatra, S, Warrington, JA, Horton, JD. Identification of a mammalian long chain fatty acyl elongase regulated by sterol regulatory element-binding proteins. J Biol Chem 2001. 276:45358-45366.

View this article via: PubMed

  1. Shimomura, I, Shimano, H, Korn, BS, Bashmakov, Y, Horton, JD. Nuclear sterol regulatory element binding proteins activate genes responsible for entire program of unsaturated fatty acid biosynthesis in transgenic mouse liver. J Biol Chem 1998. 273:35299-35306.

View this article via: PubMed

  1. Shimano, H, et al. Overproduction of cholesterol and fatty acids causes massive liver enlargement in transgenic mice expressing truncated SREBP-1a. J Clin Invest 1996. 98:1575-1584.

View this article via: JCI.org PubMed

  1. Shimano, H, et al. Isoform 1c of sterol regulatory element binding protein is less active than isoform 1a in livers of transgenic mice and in cultured cells. J Clin Invest 1997. 99:846-854.

View this article via: JCI.org PubMed

  1. Horton, JD, et al. Activation of cholesterol synthesis in preference to fatty acid synthesis in liver and adipose tissue of transgenic mice overproducing sterol regulatory element-binding protein-2. J Clin Invest 1998. 101:2331-2339.

View this article via: JCI.org PubMed

  1. Korn, BS, et al. Blunted feedback suppression of SREBP processing by dietary cholesterol in transgenic mice expressing sterol-resistant SCAP(D443N). J Clin Invest 1998. 102:2050-2060.

View this article via: JCI.org PubMed

  1. Shimano, H, et al. Elevated levels of SREBP-2 and cholesterol synthesis in livers of mice homozygous for a targeted disruption of the SREBP-1 gene. J Clin Invest 1997. 100:2115-2124.

View this article via: JCI.org PubMed

  1. Matsuda, M, et al. SREBP cleavage-activating protein (SCAP) is required for increased lipid synthesis in liver induced by cholesterol deprivation and insulin elevation. Genes Dev 2001. 15:1206-1216.

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  1. Yang, J, et al. Decreased lipid synthesis in livers of mice with disrupted Site-1 protease gene. Proc Natl Acad Sci USA 2001. 98:13607-13612.

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Liang, G, et al. Diminished hepatic response to fasting/refeeding and liver X receptor agonists in mice with selective deficiency of sterol regulatory element-binding protein-1c. J Biol Chem 2002. 277:9520-9528.

http://www.jci.org/articles/view/15593

 

Structural Biochemistry/Lipids/Membrane Lipids

< Structural Biochemistry‎ | Lipids

Membrane proteins rely on their interaction with membrane lipids to uphold its structure and maintain its functions as a protein. For membrane proteins to purify and crystallize, it is essential for the membrane protein to be in the appropriate lipid environment. Lipids assist in crystallization and stabilize the protein and provide lattice contacts. Lipids can also help obtain membrane protein structures in a native conformation. Membrane protein structures contain bound lipid molecules. Biological membranes are important in life, providing permeable barriers for cells and their organelles. The interaction between membrane proteins and lipids facilitates basic processes such as respiration, photosynthesis, transport, signal transduction and motility. These basic processes require a diverse group of proteins, which are encoded by 20-30% of an organism’s annotated genes.

There exist a great number of membrane lipids. Specifically, eukaryotic cells have a very complex collection of lipids that rely on many of the cell’s resources for its synthesis. Interactions between proteins and lipids can be very specific. Specific types of lipids can make a structure stable, provide control in insertion and folding processes, and help to assemble multisubunit complexes or supercomplexes, and most importantly, can significantly affect a membrane protein’s functions. Protein and lipid interactions are not sufficiently tight, meaning that lipids are retained during membrane protein purification. Since cellular membranes are fluid arrangements of lipids, some lipids affect interesting changes to membrane due to their characteristics. Glycosphigolipids and cholesterol tend to form small islands within the membranes, called lipid rafts, due to their physical properties. Some proteins also tend to cluster in lipid raft, while others avoid being in lipid rafts. However, the existence of lipid rafts in cells seems to be transitory.

Recent progress in determining membrane protein structure has brought attention to the importance of maintaining a favorable lipid environment so proteins to crystallize and purify successfully. Lipids assist in crystallization by stabilizing the protein fold and the relationships between subunits or monomers. The lipid content in protein-lipid detergent complexes can be altered by adjusting solubilisation and purification protocols, also by adding native or non-native lipids.

There are three type of membrane lipids: 1. Phospholipids: major class of membrane lipids. 2. glycolipids. 3. Cholesterols. Membrane lipids were started with eukaryotes and bacteria.

http://en.wikibooks.org/wiki/Structural_Biochemistry/Lipids/Membrane_Lipids

Types of Membrane Lipids

Lipids are often used as membrane constituents. The three major classes that membrane lipids are divided into are phospholipids, glycolipids, and cholesterol. Lipids are found in eukaryotes and bacteria. Although the lipids in archaea have many features that are related to the membrane formation that is similar with lipids of other organisms, they are still distinct from one another. The membranes of archaea differ in composition in three major ways. Firstly, the nonpolar chains are joined to a glycerol backbone by ether instead of esters, allowing for more resistance to hydrolysis. Second, the alkyl chains are not linear, but branched and make them more resistant to oxidation. The ability of archaeal lipids to resist hydrolysis and oxidation help these types of organisms to withstand the extreme conditions of high temperature, low pH, or high salt concentration. Lastly, the stereochemistry of the central glycerol is inverted. Membrane lipids have an extensive repertoire, but they possess a critical common structural theme in which they are amphipathic molecules, meaning they contain both a hydrophilic and hydrophobic moiety.

Membrane lipids are all closed bodies or boundaries separating substituent parts of the cell. The thickness of membranes is usually between 60 and 100 angstroms. These bodies are constructed from non-covalent assemblies. Their polar heads align with each other and their non-polar hydrocarbon tails align as well. The resulting stability is credited to hydrophobic interaction which proves to be quite stable due to the length of their hydrocarbon tails.

 

Membrane Lipids

Lipid Vesicles

Lipid vesicles, also known as liposomes, are vesicles that are essentially aqueous vesicles that are surrounded by a circular phospholipid bilayer. Like the other phospholipid structures, they have the hydrocarbon/hydrophobic tails facing inward, away from the aqueous solution, and the hydrophilic heads facing towards the aqueous solution. These vesicles are structures that form enclosed compartments of ions and solutes, and can be utilized to study the permeability of certain membranes, or to transfer these ions or solutes to certain cells found elsewhere.

Liposomes as vesicles can serve various clinical uses. Injecting liposomes containing medicine or DNA (for gene therapy) into patients is a possible method of drug delivery. The liposomes fuse with other cells’ membranes and therefore combine their contents with that of the patient’s cell. This method of drug delivery is less toxic than direct exposure because the liposomes carry the drug directly to cells without any unnecessary intermediate steps.

Because of the hydrophobic interactions among several phospholipids and glycolipids, a certain structure called the lipid bilayer or bimolecular sheet is favored. As mentioned earlier, phospholipids and glycolipids have both hydrophilic and hydrophobic moieties; thus, when several phospholipids or glycolipids come together in an aqueous solution, the hydrophobic tails interact with each other to form a hydrophobic center, while the hydrophilic heads interact with each other forming a hydrophilic coating on each side of the bilayer.

http://upload.wikimedia.org/wikibooks/en/b/ba/Liposome_final%2A.png

http://upload.wikimedia.org/wikibooks/en/f/fa/Membrane_bilayer.jpg

 

Liposome_

Liposome_

 

 

Membrane_bilayer

Membrane_bilayer

 

 

 

Evidence Report/Technology Assessment   Number 89

 

Effects of Omega-3 Fatty Acids on Lipids and Glycemic Control in Type II Diabetes and the Metabolic Syndrome and on Inflammatory Bowel Disease, Rheumatoid Arthritis, Renal Disease, Systemic Lupus Erythematosus, and Osteoporosis

 

Prepared for:

Agency for Healthcare Research and Quality

U.S. Department of Health and Human Services

540 Gaither Road

Rockville, MD 20850

http://www.ahrq.gov

Contract No. 290-02-0003

 

Chapter 1. Introduction

This report is one of a group of evidence reports prepared by three Agency for Healthcare Research and Quality (AHRQ)-funded Evidence-Based Practice Centers (EPCs) on the role of omega-3 fatty acids (both from food sources and from dietary supplements) in the prevention or treatment of a variety of diseases. These reports were requested and funded by the Office of Dietary Supplements, National Institutes of Health. The three EPCs – the Southern California EPC (SCEPC, based at RAND), the Tufts-New England Medical Center (NEMC) EPC, and the University of Ottawa EPC – have each produced evidence reports. To ensure consistency of approach, the three EPCs collaborated on selected methodological elements, including literature search strategies, rating of evidence, and data table design.

The aim of these reports is to summarize the current evidence on the effects of omega-3 fatty acids on prevention and treatment of cardiovascular diseases, cancer, child and maternal health, eye health, gastrointestinal/renal diseases, asthma, immune- mediated diseases, tissue/organ transplantation, mental health, and neurological diseases and conditions. In addition to informing the research community and the public on the effects of omega-3 fatty acids on various health conditions, it is anticipated that the findings of the reports will also be used to help define the agenda for future research.

This report focuses on the effects of omega-3 fatty acids on immune- mediated diseases, bone metabolism, and gastrointestinal/renal diseases. Subsequent reports from the SCEPC will focus on cancer and neurological diseases and conditions.

This chapter provides a brief review of the current state of knowledge about the metabolism, physiological functions, and sources of omega-3 fatty acids.

 

The Recognition of Essential Fatty Acids

Dietary fat has long been recognized as an important source of energy for mammals, but in the late 1920s, researchers demonstrated the dietary requirement for particular fatty acids, which came to be called essential fatty acids. It was not until the advent of intravenous feeding, however, that the importance of essential fatty acids was widely accepted: Clinical signs of essential fatty acid deficiency are generally observed only in patients on total parenteral nutrition who received mixtures devoid of essential fatty acids or in those with malabsorption syndromes.

These signs include dermatitis and changes in visual and neural function. Over the past 40 years, an increasing number of physiological functions, such as immunomodulation, have been attributed to the essential fatty acids and their metabolites, and this area of research remains quite active.1, 2

Fatty Acid Nomenclature

The fat found in foods consists largely of a heterogeneous mixture of triacylglycerols (triglycerides)–glycerol molecules that are each combined with three fatty acids. The fatty acids can be divided into two categories, based on chemical properties: saturated fatty acids, which are usually solid at room temperature, and unsaturated fatty acids, which are liquid at room temperature. The term “saturation” refers to a chemical structure in which each carbon atom in the fatty acyl chain is bound to (saturated with) four other atoms, these carbons are linked by single bonds, and no other atoms or molecules can attach; unsaturated fatty acids contain at least one pair of carbon atoms linked by a double bond, which allows the attachment of additional atoms to those carbons (resulting in saturation). Despite their differences in structure, all fats contain approximately the same amount of energy (37 kilojoules/gram, or 9 kilocalories/gram).

The class of unsaturated fatty acids can be further divided into monounsaturated and polyunsaturated fatty acids. Monounsaturated fatty acids (the primary constituents of olive and canola oils) contain only one double bond. Polyunsaturated fatty acids (PUFAs) (the primary constituents of corn, sunflower, flax seed and many other vegetable oils) contain more than one double bond. Fatty acids are often referred to using the number of carbon atoms in the acyl chain, followed by a colon, followed by the number of double bonds in the chain (e.g., 18:1 refers to the 18-carbon monounsaturated fatty acid, oleic acid; 18:3 refers to any 18-carbon PUFA with three double bonds).

PUFAs are further categorized on the basis of the location of their double bonds. An omega or n notation indicates the number of carbon atoms from the methyl end of the acyl chain to the first double bond. Thus, for example, in the omega-3 (n-3) family of PUFAs, the first double bond is 3 carbons from the methyl end of the molecule. The trivial names, chemical names and abbreviations for the omega-3 fatty acids are detailed in Table 1.1.  Finally, PUFAs can be categorized according to their chain length. The 18-carbon n-3 and n-6 short-chain PUFAs are precursors to the longer 20- and 22-carbon PUFAs, called long-chain PUFAs (LCPUFAs).

Fatty Acid Metabolism

Mammalian cells can introduce double bonds into all positions on the fatty acid chain except the n-3 and n-6 position. Thus, the short-chain alpha- linolenic acid (ALA, chemical abbreviation: 18:3n-3) and linoleic acid (LA, chemical abbreviation: 18:2n-6) are essential fatty acids.

No other fatty acids found in food are considered ‘essential’ for humans, because they can all be synthesized from the short chain fatty acids.

Following ingestion, ALA and LA can be converted in the liver to the long chain, more unsaturated n-3 and n-6 LCPUFAs by a complex set of synthetic pathways that share several enzymes (Figure 1). LC PUFAs retain the original sites of desaturation (including n-3 or n-6). The omega-6 fatty acid LA is converted to gamma-linolenic acid (GLA, 18:3n-6), an omega- 6 fatty acid that is a positional isomer of ALA. GLA, in turn, can be converted to the longerchain omega-6 fatty acid, arachidonic acid (AA, 20:4n-6). AA is the precursor for certain classes of an important family of hormone- like substances called the eicosanoids (see below).

The omega-3 fatty acid ALA (18:3n-3) can be converted to the long-chain omega-3 fatty acid, eicosapentaenoic acid (EPA; 20:5n-3). EPA can be elongated to docosapentaenoic acid (DPA 22:5n-3), which is further desaturated to docosahexaenoic acid (DHA; 22:6n-3). EPA and DHA are also precursors of several classes of eicosanoids and are known to play several other critical roles, some of which are discussed further below.

The conversion from parent fatty acids into the LC PUFAs – EPA, DHA, and AA – appears to occur slowly in humans. In addition, the regulation of conversion is not well understood, although it is known that ALA and LA compete for entry into the metabolic pathways.

Physiological Functions of EPA and AA

As stated earlier, fatty acids play a variety of physiological roles. The specific biological functions of a fatty acid are determined by the number and position of double bonds and the length of the acyl chain.

Both EPA (20:5n-3) and AA (20:4n-6) are precursors for the formation of a family of hormone- like agents called eicosanoids. Eicosanoids are rudimentary hormones or regulating – molecules that appear to occur in most forms of life. However, unlike endocrine hormones, which travel in the blood stream to exert their effects at distant sites, the eicosanoids are autocrine or paracrine factors, which exert their effects locally – in the cells that synthesize them or adjacent cells. Processes affected include the movement of calcium and other substances into and out of cells, relaxation and contraction of muscles, inhibition and promotion of clotting, regulation of secretions including digestive juices and hormones, and control of fertility, cell division, and growth.3

The eicosanoid family includes subgroups of substances known as prostaglandins, leukotrienes, and thromboxanes, among others. As shown in Figure 1.1, the long-chain omega-6 fatty acid, AA (20:4n-6), is the precursor of a group of eicosanoids that include series-2 prostaglandins and series-4 leukotrienes. The omega-3 fatty acid, EPA (20:5n-3), is the precursor to a group of eicosanoids that includes series-3 prostaglandins and series-5 leukotrienes. The AA-derived series-2 prostaglandins and series-4 leukotrienes are often synthesized in response to some emergency such as injury or stress, whereas the EPA-derived series-3 prostaglandins and series-5 leukotrienes appear to modulate the effects of the series-2 prostaglandins and series-4 leukotrienes (usually on the same target cells). More specifically, the series-3 prostaglandins are formed at a slower rate and work to attenuate the effects of excessive levels of series-2 prostaglandins. Thus, adequate production of the series-3 prostaglandins seems to protect against heart attack and stroke as well as certain inflammatory diseases like arthritis, lupus, and asthma.3.

EPA (22:6 n-3) also affects lipoprotein metabolism and decreases the production of substances – including cytokines, interleukin 1ß (IL-1ß), and tumor necrosis factor a (TNF-a) – that have pro-inflammatory effects (such as stimulation of collagenase synthesis and the expression of adhesion molecules necessary for leukocyte extravasation [movement from the circulatory system into tissues]).2 The mechanism responsible for the suppression of cytokine production by omega-3 LC PUFAs remains unknown, although suppression of omega-6-derived eicosanoid production by omega-3 fatty acids may be involved, because the omega-3 and omega-6 fatty acids compete for a common enzyme in the eicosanoid synthetic pathway, delta-6 desaturase.

DPA (22:5n-3) (the elongation product of EPA) and its metabolite DHA (22:6n-3) are frequently referred to as very long chain n-3 fatty acids (VLCFA). Along with AA, DHA is the major PUFA found in the brain and is thought to be important for brain development and function. Recent research has focused on this role and the effect of supplementing infant formula with DHA (since DHA is naturally present in breast milk but not in formula).

Dietary Sources and Requirements

Both ALA and LA are present in a variety of foods. LA is present in high concentrations in many commonly used oils, including safflower, sunflower, soy, and corn oil. ALA is present in some commonly used oils, including canola and soybean oil, and in some leafy green vegetables. Thus, the major dietary sources of ALA and LA are PUFA-rich vegetable oils. The proportion of LA to ALA as well as the proportion of those PUFAs to others varies considerably by the type of oil. With the exception of flaxseed, canola, and soybean oil, the ratio of LA to ALA in vegetable oils is at least 10 to 1. The ratios of LA to ALA for flaxseed, canola, and soy are approximately 1: 3.5, 2:1, and 8:1, respectively; however, flaxseed oil is not typically consumed in the North American diet. It is estimated that on average in the U.S., LA accounts for 89% of the total PUFAs consumed, and ALA accounts for 9%. Another estimate suggests that Americans consume 10 times more omega-6 than omega-3 fatty acids.4 Table 1.2 shows the proportion of omega 3 fatty acids for a number of foods.

Syntheis and Degradation

Source of Acetyl CoA for Fatty Acid Synthesis

Source of Acetyl CoA for Fatty Acid Synthesis

step 1

step 1

condensation reaction with malonyl ACP

ACP (acyl carrier protein)

ACP (acyl carrier protein)

synthesis requires acetyl CoA from citrate shuttle

synthesis requires acetyl CoA from citrate shuttle

conversion to fatty acyl co A in cytoplasm

conversion to fatty acyl co A in cytoplasm

ACP (acyl carrier protein)

ACP (acyl carrier protein)

FA synthesis not exactly reverse of catabolism

FA synthesis not exactly reverse of catabolism

 

Fatty Acid Synthase

Fatty Acid Synthase

complete FA synthesis

complete FA synthesis

Desaturation

Desaturation

Elongation and Desaturation of Fatty Acids

Elongation and Desaturation of Fatty Acids

release of FAs from adiposites

release of FAs from adiposites

Fatty acid beta oxidation and Krebs cycle produce NAD, NADH, FADH2

Fatty acid beta oxidation and Krebs cycle produce NAD, NADH, FADH2

ketone bodies

ketone bodies

metabolism of ketone bodies

metabolism of ketone bodies

Arachidonoyl-mimicking

Arachidonoyl-mimicking

Arachidonate pathways

Arachidonate pathways

arachidonic acid derivatives

arachidonic acid derivatives

major metabolic intermediates in the pathways for synthesis of cholesterol, fatty acids, and triglycerides

major metabolic intermediates in the pathways for synthesis of cholesterol, fatty acids, and triglycerides

Model for the sterol-mediated proteolytic release of SREBPs from membrane

Model for the sterol-mediated proteolytic release of SREBPs from membrane

hormone regulation

hormone regulation

 insulin receptor and and insulin receptor signaling pathway (IRS)

insulin receptor and and insulin receptor signaling pathway (IRS)

 islet brain glucose signaling

islet brain glucose signaling

 

 

 

 

 

 

 

 

Fish source

Fish source

omega FAs

omega FAs

 

Excessive omega 6s

Excessive omega 6s

omega 6s

omega 6s

diet and cancer

diet and cancer

Patients at risk of FA deficiency

Patients at risk of FA deficiency

PPAR role

PPAR role

PPAR role

PPAR role

Omega 6_3 pathways

Omega 6_3 pathways

n3 vs n6 PUFAs

n3 vs n6 PUFAs

triene-teraene ratio

triene-teraene ratio

arachidonic acid, leukotrienes, PG and thromboxanes

arachidonic acid, leukotrienes, PG and thromboxanes

Cox 2 and cancer

Cox 2 and cancer

Lipidomics of atherosclerotic plaques

Lipidomics of atherosclerotic plaques

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Effect of TPN on EFAD

Effect of TPN on EFAD

benefits of omega 3s

benefits of omega 3s

food consumption

food consumption

 

Read Full Post »

Selected References to Signaling and Metabolic Pathways in PharmaceuticalIntelligence.com

Curator: Larry H. Bernstein, MD, FCAP

 

This is an added selection of articles in Leaders in Pharmaceutical Intelligence after the third portion of the discussion in a series of articles that began with signaling and signaling pathways. There are fine features on the functioning of enzymes and proteins, on sequential changes in a chain reaction, and on conformational changes that we shall return to.  These are critical to developing a more complete understanding of life processes.  I have indicated that many of the protein-protein interactions or protein-membrane interactions and associated regulatory features have been referred to previously, but the focus of the discussion or points made were different.

  1. Signaling and signaling pathways
  2. Signaling transduction tutorial.
  3. Carbohydrate metabolism3.1  Selected References to Signaling and Metabolic Pathways in Leaders in Pharmaceutical Intelligence
  4. Lipid metabolism
  5. Protein synthesis and degradation
  6. Subcellular structure
  7. Impairments in pathological states: endocrine disorders; stress hypermetabolism; cancer.

Selected References to Signaling and Metabolic Pathwayspublished in this Open Access Online Scientific Journal, include the following:

Update on mitochondrial function, respiration, and associated disorders

Curator and writer: Larry H. Benstein, MD, FCAP

http://pharmaceuticalintelligence.com/2014/07/08/update-on-mitochondrial-function-respiration-and-associated-disorders/

A Synthesis of the Beauty and Complexity of How We View Cancer


Cancer Volume One – Summary

A Synthesis of the Beauty and Complexity of How We View Cancer

Author: Larry H. Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2014/03/26/a-synthesis-of-the-beauty-and-complexity-of-how-we-view-cancer/

Introduction – The Evolution of Cancer Therapy and Cancer Research: How We Got Here?

Author and Curator: Larry H Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2014/04/04/introduction-the-evolution-of-cancer-therapy-and-cancer-research-how-we-got-here/

 The Centrality of Ca(2+) Signaling and Cytoskeleton Involving Calmodulin Kinases and Ryanodine Receptors in Cardiac Failure, Arterial Smooth Muscle, Post-ischemic Arrhythmia, Similarities and Differences, and Pharmaceutical Targets

Author and Curator: Larry H Bernstein, MD, FCAP, 
Author, and Content Consultant to e-SERIES A: Cardiovascular Diseases: Justin Pearlman, MD, PhD, FACC
And Curator: Aviva Lev-Ari, PhD, RN

http://pharmaceuticalintelligence.com/2013/09/08/the-centrality-of-ca2-signaling-and-cytoskeleton-involving-calmodulin-kinases-and-ryanodine-receptors-in-cardiac-failure

Renal Distal Tubular Ca2+ Exchange Mechanism in Health and Disease

Author and Curator: Larry H. Bernstein, MD, FCAP
Curator:  Stephen J. Williams, PhD
and Curator: Aviva Lev-Ari, PhD, RN

http://pharmaceuticalintelligence.com/2013/09/02/renal-distal-tubular-ca2-exchange-mechanism-in-health-and-disease/

Mitochondrial Metabolism and Cardiac Function

Curator: Larry H Bernstein, MD, FACP

http://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-metabolism-and-cardiac-function/

Mitochondrial Dysfunction and Cardiac Disorders

Curator: Larry H Bernstein, MD, FACP

http://pharmaceuticalintelligence.com/2013/04/14/mitochondrial-metabolism-and-cardiac-function/

Reversal of Cardiac mitochondrial dysfunction

Curator: Larry H Bernstein, MD, FACP

http://pharmaceuticalintelligence.com/2013/04/14/reversal-of-cardiac-mitochondrial-dysfunction/

Advanced Topics in Sepsis and the Cardiovascular System  at its End Stage

Author: Larry H Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2013/08/18/advanced-topics-in-Sepsis-and-the-Cardiovascular-System-at-its-End-Stage/

Ubiquinin-Proteosome pathway, autophagy, the mitochondrion, proteolysis and cell apoptosis

Curator: Larry H Bernstein, MD, FACP

http://pharmaceuticalintelligence.com/2012/10/30/ubiquinin-proteosome-pathway-autophagy-the-mitochondrion-proteolysis-and-cell-apoptosis/

Ubiquitin-Proteosome pathway, Autophagy, the Mitochondrion, Proteolysis and Cell Apoptosis: Part III

Curator: Larry H Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2013/02/14/ubiquinin-proteosome-pathway-autophagy-the-mitochondrion-proteolysis-and-cell-apoptosis-reconsidered/

 

Nitric Oxide, Platelets, Endothelium and Hemostasis (Coagulation Part II)

Curator: Larry H. Bernstein, MD, FCAP 

http://pharmaceuticalintelligence.com/2012/11/08/nitric-oxide-platelets-endothelium-and-hemostasis/


Mitochondrial Damage and Repair under Oxidative Stress

Curator: Larry H Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2012/10/28/mitochondrial-damage-and-repair-under-oxidative-stress/

Mitochondria: Origin from oxygen free environment, role in aerobic glycolysis, metabolic adaptation

Reporter and Curator: Larry H Bernstein, MD, FACP

http://pharmaceuticalintelligence.com/2012/09/26/mitochondria-origin-from-oxygen-free-environment-role-in-aerobic-glycolysis-metabolic-adaptation/

 

Nitric Oxide has a Ubiquitous Role in the Regulation of Glycolysis – with a Concomitant Influence on Mitochondrial Function

Reporter, Editor, and Topic Co-Leader: Larry H. Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2012/09/16/nitric-oxide-has-a-ubiquitous-role-in-the-regulation-of-glycolysis-with-a-concomitant-influence-on-mitochondrial-function/


Mitochondria and Cancer: An overview of mechanisms

Author and Curator: Ritu Saxena, Ph.D.

http://pharmaceuticalintelligence.com/2012/09/01/mitochondria-and-cancer-an-overview/

Mitochondria: More than just the “powerhouse of the cell”

Author and Curator: Ritu Saxena, Ph.D.

http://pharmaceuticalintelligence.com/2012/07/09/mitochondria-more-than-just-the-powerhouse-of-the-cell/

Overview of Posttranslational Modification (PTM)

Curator: Larry H. Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2014/07/29/overview-of-posttranslational-modification-ptm/


Ubiquitin Pathway Involved in Neurodegenerative Diseases

Author and curator: Larry H Bernstein, MD,  FCAP

http://pharmaceuticalintelligence.com/2013/02/15/ubiquitin-pathway-involved-in-neurodegenerative-diseases/

Is the Warburg Effect the Cause or the Effect of Cancer: A 21st Century View?

Author: Larry H. Bernstein, MD, FCAP 

http://pharmaceuticalintelligence.com/2012/10/17/is-the-warburg-effect-the-cause-or-the-effect-of-cancer-a-21st-century-view/

New Insights on Nitric Oxide donors – Part IV

Curator and Author: Larry H. Bernstein, MD, FCAP

http://pharmaceuticalintelligence.com/2012/11/26/new-insights-on-no-donors/

Perspectives on Nitric Oxide in Disease Mechanisms [Kindle Edition]

Margaret Baker PhD (Author), Tilda Barliya PhD (Author), Anamika Sarkar PhD (Author), Ritu Saxena PhD (Author), Stephen J. Williams PhD (Author), Larry Bernstein MD FCAP (Editor), Aviva Lev-Ari PhD RN (Editor), Aviral Vatsa PhD (Editor)

http://pharmaceuticalintelligence.com/biomed-e-books/series-a-e-books-on-cardiovascular-diseases/perspectives-on-nitric-oxide-in-disease-mechanisms-v2/

 

Summary

Nitric oxide and its role in vascular biology

Signal transmission by a gas that is produced by one cell, penetrates through membranes and regulates the function of another cell represents an entirely new principle for signaling in biological systems.   All compounds that inhibit endothelium-derived relaxation-factor (EDRF) have one property in common, redox activity, which accounts for their inhibitory action on EDRF. One exception is hemoglobin, which inactivates EDRF by binding to it. Furchgott, Ignarro and Murad received the Nobel Prize in Physiology and Medicine for discovery of EDRF in 1998 and demonstrating that it might be nitric oxide (NO) based on a study of the transient relaxations of endothelium-denuded rings of rabbit aorta.  These investigators working independently demonstrated that NO is indeed produced by mammalian cells and that NO has specific biological roles in the human body. These studies highlighted the role of NO in cardiovascular, nervous and immune systems. In cardiovascular system NO was shown to cause relaxation of vascular smooth muscle cells causing vasodilatation, in nervous system NO acts as a signaling molecule and in immune system it is used against pathogens by the phagocytosis cells. These pioneering studies opened the path of investigation of role of NO in biology.

NO modulates vascular tone, fibrinolysis, blood pressure and proliferation of vascular smooth muscles. In cardiovascular system disruption of NO pathways or alterations in NO production can result in preponderance to hypertension, hypercholesterolemia, diabetes mellitus, atherosclerosis and thrombosis. The three enzyme isoforms of NO synthase family are responsible for generating NO in different tissues under various circumstances.

Reduction in NO production is implicated as one of the initial factors in initiating endothelial dysfunction. This reduction could be due to

  • reduction in eNOS production
  • reduction in eNOS enzymatic activity
  • reduced bioavailability of NO

Nitric oxide is one of the smallest molecules involved in physiological functions in the body. It is seeks formation of chemical bonds with its targets.  Nitric oxide can exert its effects principally by two ways:

  • Direct
  • Indirect

Direct actions, as the name suggests, result from direct chemical interaction of NO with its targets e.g. with metal complexes, radical species. These actions occur at relatively low NO concentrations (<200 nM)

Indirect actions result from the effects of reactive nitrogen species (RNS) such as NO2 and N2O3. These reactive species are formed by the interaction of NO with superoxide or molecular oxygen. RNS are generally formed at relatively high NO concentrations (>400 nM)

Although it can be tempting for scientists to believe that RNS will always have deleterious effects and NO will have anabolic effects, this is not entirely true as certain RNS mediated actions mediate important signalling steps e.g. thiol oxidation and nitrosation of proteins mediate cell proliferation and survival, and apoptosis respectively.

  • Cells subjected to NO concentration between 10-30 nM were associated with cGMP dependent phosphorylation of ERK
  • Cells subjected to NO concentration between 30-60 nM were associated with Akt phosphorylation
  • Concentration nearing 100 nM resulted in stabilisation of hypoxia inducible factor-1
  • At nearly 400 nM NO, p53 can be modulated
  • >1μM NO, it nhibits mitochondrial respiration

 

Nitric oxide signaling, oxidative stress,  mitochondria, cell damage

Recent data suggests that other NO containing compounds such as S- or N-nitrosoproteins and iron-nitrosyl complexes can be reduced back to produce NO. These NO containing compounds can serve as storage and can reach distant tissues via blood circulation, remote from their place of origin. Hence NO can have both paracrine and ‘endocrine’ effects.

Intracellularly the oxidants present in the cytosol determine the amount of bioacitivity that NO performs. NO can travel roughly 100 microns from NOS enzymes where it is produced.

NO itself in low concentrations have protective action on mitochondrial signaling of cell death.

The aerobic cell was an advance in evolutionary development, but despite the energetic advantage of using oxygen, the associated toxicity of oxygen abundance required adaptive changes.

Oxidation-reduction reactions that are necessary for catabolic and synthetic reactions, can cumulatively damage the organism associated with cancer, cardiovascular disease, neurodegerative disease, and inflammatory overload.  The normal balance between production of pro-oxidant species and destruction by the antioxidant defenses is upset in favor of overproduction of the toxic species, which leads to oxidative stress and disease.

We reviewed the complex interactions and underlying regulatory balances/imbalances between the mechanism of vasorelaxation and vasoconstriction of vascular endothelium by way of nitric oxide (NO), prostacyclin, in response to oxidative stress and intimal injury.

Nitric oxide has a ubiquitous role in the regulation of glycolysis with a concomitant influence on mitochondrial function. The influence on mitochondrial function that is active in endothelium, platelets, vascular smooth muscle and neural cells and the resulting balance has a role in chronic inflammation, asthma, hypertension, sepsis and cancer.

Potential cytotoxic mediators of endothelial cell (EC) apoptosis include increased formation of reactive oxygen and nitrogen species (ROSRNS) during the atherosclerotic process. Nitric oxide (NO) has a biphasic action on oxidative cell killing with low concentrations protecting against cell death, whereas higher concentrations are cytotoxic.

ROS induces mitochondrial DNA damage in ECs, and this damage is accompanied by a decrease in mitochondrial RNA (mtRNA) transcripts, mitochondrial protein synthesis, and cellular ATP levels.

NO and circulatory diseases

Blood vessels arise from endothelial precursors that are thin, flat cells lining the inside of blood vessels forming a monolayer throughout the circulatory system. ECs are defined by specific cell surface markers that characterize their phenotype.

Scientists at the University of Helsinki, Finland, wanted to find out if there exists a rare vascular endothelial stem cell (VESC) population that is capable of producing very high numbers of endothelial daughter cells, and can lead to neovascular growth in adults.

VESCs discovered that reside at the blood vessel wall endothelium are a small population of CD117+ ECs capable of self-renewal.  These cells are capable of undergoing clonal expansion unlike the surrounding ECs that bear limited proliferating potential. A single VESC cell isolated from the endothelial population was able to generate functional blood vessels.

Among many important roles of Nitric oxide (NO), one of the key actions is to act as a vasodilator and maintain cardiovascular health. Induction of NO is regulated by signals in tissue as well as endothelium.

Chen et. al. (Med. Biol. Eng. Comp., 2011) developed a 3-D model consisting of two branched arterioles and nine capillaries surrounding the vessels. Their model not only takes into account of the 3-D volume, but also branching effects on blood flow.

The model indicates that wall shear stress changes depending upon the distribution of RBC in the microcirculations of blood vessels, lead to differential production of NO along the vascular network.

Endothelial dysfunction, the hallmark of which is reduced activity of endothelial cell derived nitric oxide (NO), is a key factor in developing atherosclerosis and cardiovascular disease. Vascular endothelial cells play a pivotal role in modulation of leukocyte and platelet adherence, thrombogenicity, anticoagulation, and vessel wall contraction and relaxation, so that endothelial dysfunction has become almost a synonym for vascular disease. A single layer of endothelial cells is the only constituent of capillaries, which differ from other vessels, which contain smooth muscle cells and adventitia. Capillaries directly mediate nutritional supply as well as gas exchange within all organs. The failure of the microcirculation leads to tissue apoptosis/necrosis.

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Carbohydrate Metabolism

Author and Curator: Larry H. Bernstein, MD, FCAP

This is the portion of the discussion in a series of articles that began with signaling and signaling pathways. There are features on the functioning of enzymes and proteins, on sequential changes in a chain reaction, and on conformational changes that we shall return to.  These are critical to developing a more complete understanding of life processes.  I have indicated that many of the protein-protein interactions or protein-membrane interactions and associated regulatory features have been referred to previously, but the focus of the discussion or points made were different.  Even though I considered placing this after the discussion of proteins and how they play out their essential role, I needed to lay out the scope of metabolic reactions and pathways, and their complementary changes. These may not appear to be adaptive, if the circumstances and the duration is not clear. The metabolic pathways map in total is in interaction with environmental conditions – light, heat, external nutrients and minerals, and toxins – all of which give direction and strength to these reactions. I shall again take from Wikipedia, as needed, and also follow mechanisms and examples from the literature, which give insight into the developments in cell metabolism. A developing goal is to discover how views introduced by molecular biology and genomics don’t clarify functional cellular dynamics that are not related to the classical view.  The work is vast.

  1. Signaling and signaling pathways
  2. Signaling transduction tutorial.
  3. Carbohydrate metabolism
  4. Lipid metabolism
  5. Protein synthesis and degradation
  6. Subcellular structure
  7. Impairments in pathological states: endocrine disorders; stress hypermetabolism; cancer.

Carbohydrate metabolism

Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms.

The most important carbohydrate is glucose, a simple sugar (monosaccharide) that is metabolized by nearly all known organisms. Glucose and other carbohydrates are part of a wide variety of metabolic pathways across species: plants synthesize carbohydrates from carbon dioxide and water by photosynthesis storing the absorbed energy internally, often in the form of starch or lipids. Plant components are consumed by animals and fungi, and used as fuel for cellular respiration. Oxidation of one gram of carbohydrate yields approximately 4 kcal of energy and from lipids about 9 kcal. Energy obtained from metabolism (e.g. oxidation of glucose) is usually stored temporarily within cells in the form of ATP.[1] Organisms capable of aerobic respiration metabolize glucose and oxygen to release energy with carbon dioxide and water as byproducts.

Complex carbohydrates contain three or more sugar units linked in a chain, with most containing hundreds to thousands of sugar units. They are digested by enzymes to release the simple sugars.
I shall not go into the digestion, breakdown and absorption of these sugar molecules. Carbohydrates are used for short-term fuel, and the most important is glucose.  Even though they are simpler to metabolize than fats or those amino acids (components of proteins) that can be used for fuel, they do not produce as effect an energy yield measured by ATP.  In animals, The concentration of glucose in the blood is linked to the pancreatic endocrine hormone, insulin.

Carbohydrates are typically stored as long polymers of glucose molecules with glycosidic bonds for structural support (e.g. chitin, cellulose) or for energy storage (e.g. glycogen, starch). However, the strong affinity of most carbohydrates for water makes storage of large quantities of carbohydrates inefficient due to the large molecular weight of the solvated water-carbohydrate complex. In most organisms, excess carbohydrates are regularly catabolised to form acetyl-CoA, which is a feed stock for the fatty acid synthesis pathway; fatty acids, triglycerides, and other lipids are commonly used for long-term energy storage. The hydrophobic character of lipids makes them a much more compact form of energy storage than hydrophilic carbohydrates. However, animals, including humans, lack the necessary enzymatic machinery and so do not synthesize glucose from lipids, though glycerol can be converted to glucose.[6]

Metabolic pathways in eukaryotes

  • Carbon fixation, or photosynthesis, in which CO2 is reduced to carbohydrate.  [omitted]
  • Glycolysis – the metabolism of glucose molecules to obtain ATP and pyruvate[7] by way of first splitting a six-carbon into two three csrbon chains, which are converted to lactic acid from pyruvate in the lactic dehydrogenase reaction. The reverse conversion is by a separate unidirectional reaction back to pyruvate after moving through pyruvate dehydrogenase complex.[8]
  • Krebs, tricarboxylic acic, or citric acid cycle
    • Typically, a breakdown of one molecule of glucose by aerobic respiration (i.e. involving both glycolysis and Kreb’s cycle) is about 33-35 ATP.[1] This is categorized as:
  • Glycogenolysis – the breakdown of glycogen into glucose, which provides a glucose supply for glucose-dependent tissues.
    • Glycogenolysis in liver provides circulating glucose short term.
    • Glycogenolysis in muscle is obligatory for muscle contraction.
    •     Anaerobic breakdown by glycolysis – yielding 8-10 ATP
    •     Aerobic respiration by kreb’s cycle – yielding 25 ATP
  • The pentose phosphate pathway (shunt) converts hexoses into pentoses and regenerates NADPH.[9] NADPH is an essential antioxidant in cells which prevents oxidative damage and acts as precursor for production of many biomolecules.
  • Glycogenesis – the conversion of excess glucose into glycogen as a cellular storage mechanism; achieving low osmotic pressure.
  • Gluconeogenesisde novo synthesis of glucose molecules from simple organic compounds. An example in humans is the conversion of a few amino acids in cellular protein to glucose.
    Metabolic use of glucose is highly important as an energy source for muscle cells and in the brain, and red blood cells.

Glucoregulation

The hormone insulin is the primary glucose regulatory signal in animals. It mainly promotes glucose uptake by the cells,  and causes liver to store excess glucose as glycogen. Its absence turns off glucose uptake, reverses electrolyte adjustments, begins glycogen breakdown and glucose release into the circulation by some cells, begins lipid release from lipid storage cells, etc. The level of circulatory glucose (known informally as “blood sugar”) is the most important signal to the insulin-producing cells. Because the level of circulatory glucose is largely determined by the intake of dietary carbohydrates, diet controls major aspects of metabolism via insulin. In humans, insulin is made by beta cells in the pancreas, fat is stored in adipose tissue cells, and glycogen is both stored and released as needed by liver cells. Regardless of insulin levels, no glucose is released to the blood from internal glycogen stores from muscle cells.

The hormone glucagon, on the other hand, opposes that of insulin, forcing the conversion of glycogen in liver cells to glucose, and then release into the blood. Muscle cells, however, lack the ability to export glucose into the blood. The release of glucagon is precipitated by low levels of blood glucose. Other hormones, notably growth hormone, cortisol, and certain catecholamines (such as epinepherine) have glucoregulatory actions similar to glucagon.  These hormones are referred to as stress hormones because they are released under the influence of catabolic proinflammatory (stress) cytokines – interleukin-1 (IL1) and tumor necrosis factor α (TNFα).

metabolic pathways

metabolic pathways

Glycemic control in DM

Glycemic control in DM

  1. Catabolic proinflammatory cytokines. Argilés JM1López-Soriano FJ. Curr Opin Clin Nutr Metab Care.1998 May;1(3):245-51.
  2. Tumor necrosis factor as a mediator of shock, cachexia and inflammation. Cerami A. Blood Purif. 1993; 11(2):108-17.
  3. Mediators of cytokine-induced insulin resistance in obesity and other inflammatory settings. Marette A. Curr Opin Clin Nutr Metab Care. 2002 Jul; 5(4):377-83.
  4. Inflammation: the link between insulin resistance, obesity and diabetes. Dandona P, Aljada A, Bandyopadhyay A. Trends Immunol. 2004 Jan; 25(1):4-7
  5. Proinflammatory cytokines and skeletal muscle. Späte U1, Schulze PC. Curr Opin Clin Nutr Metab Care. 2004 May;7(3):265-9.
  6. Insulin-like growth factor-1 and muscle wasting in chronic heart failure. Schulze PC, Späte U. Int J Biochem Cell Biol. 2005 Oct; 37(10):2023-35.
  7. IGF-I stimulates muscle growth by suppressing protein breakdown and expression of atrophy-related ubiquitin ligases, atrogin-1 and MuRF1. Sacheck JM, Ohtsuka A, McLary SC, Goldberg AL. Am J Physiol Endocrinol Metab. 2004 Oct; 287(4):E591-601. Epub 2004 Apr 20.

Glycolysis – Animation and Notes

By Sweety Mehta – Sept 20, 2011  in: Animations, Biochemistry Animations, Biochemistry Notes

http://pharmaxchange.info/press/2011/09/glycolysis-animation-and-notes/

Cellular respiration involves breaking the bonds of glucose to produce energy in the form of ATP (adenosine triphosphate). The total energy produced during glucose metabolism is described at Energetics of Cellular Respiration. Glycolysis is the most critical phase in glucose metabolism during cellular respiration. The term “glycolysis” literally means breakdown of glucose and sugars. Biochemically, it involves the breakdown of glucose to pyruvate (or pyruvic acid) via a series of enzymes. Glycolysis does not require molecular oxygen and is hence considered anaerobic. Therefore, it is a common pathway for all living organisms.

Glycolysis is followed by

Kreb’s cycle in the stages of cellular respiration.

Glycolysis is said to occur in two phases:

  1. The Preparatory Phase: From glucose till formation of Glyceraldehyde 3-Phosphate (GADP)
  2. The Pay-off Phase: From Glyceraldehyde-3-Phosphate (GADP) to the final product pyruvate

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.

glycolysis

The animation below gives an outline of the entire pathway of glucose metabolism by glycolysis

Note – The animation is best played in full screen. To go forward in the animation, press the Play button. To skip the whole section press the forward button. To go back press the rewind button.

The Preparatory Phase

In this stage of the cycle, ATP or energy is actually consumed and is hence also known as the investment phase of glycolysis.

Step 1, involves the conversion of glucose to glucose-6-phosphate (G6P) with the help of the enzyme hexokinase and the consumption of 1 molecule of ATP. This reaction helps keep the concentration of glucose low in the cell, allowing for more absorption of glucose into it. Additionally, G6P is not transported out of the cell as there are no G6P transporters on the cell.

Step 2 involves the rearrangement of glucose-6-phosphate to fructose-6-phosphate (F6P) with the help of the enzyme phosphohexose isomerase in a reversible manner. Fructose can directly enter the glycolysis pathway at this point. This isomerization to a keto-sugar such as fructose is essential for carbanion stabilization required for the next step.

Step 3 involves the phosphorylation of fructose-6-phosphate to fructose-1,6-biphosphate (F1,6BP) by the use of 1 molecule of ATP and the enzyme phosphofructokinase-1 (PPK1). This phosphorylation step destabilizes the molecule and helps drive the next reaction which ensures breakdown of the molecule to a 3-carbon unit.

Step 4 involves the breakdown of fructose-1,6-biphosphate (6 carbons) to two molecules of 3-carbon units i.e. glyceralde 3-phosphate (GADP) and Dihydroxyacetone phosphate (DHAP). The GADP can be interconverted to DHAP by enzyme triose phosphate isomerase.

The Pay-Off Phase

In this stage of the cycle, ATP or energy is produced either in the form of ATP alone or in the form of NADH + H+ which can be later converted to ATP via the electron transport chain (ETS). In this since energy is restored it is known as the pay-off phase of glycolysis. All steps in this phase occur with 2 molecules of the substrates each as indicated in the brackets by the name of the molecules.

Step 1, involves the dehydrogenation of glyceraldehyde-3-phosphate (GADP) to 1,3-biphophoglycerate (1,3BPG) by the use of 2 molecules of inorganic phosphate (Pi) with the production of 2 molecules of NADH + H+ in the presence of the enzyme glyceraldehyde 3-phosphate dehydrogenase.

Step 2, in this step dephosphorylation of 1,3-biphosphoglycerate (1,3BPG) to 3-phospoglycerate (3PG) produces 2 molecules of ATP by the enzyme phosphoglycerate kinase.

Step 3, involves the isomerisation of 3-phosphoglycerate (3PG) to 2-phosphoglycerate (2PG) by the enzyme phosphoglycerate mutase in a reversible manner.

Step 4 involves the enolization of 2-phosphoglycerate (2PG) to phosphoenolpyruvate (PEP) with the loss of one molecule of water in the presence of enzyme enolase.

Step 5 is the final step of the glycolysis pathway and it involves the dephosphorylation of the phosphoenolpyruvate (PEP) to pyruvate by enzyme pyruvate kinase to produce 2 more molecules of ATP.

Net Yield of Glycolysis

  1. The preparatory phase consumes 2 ATP
  2. The pay-off phase produces 4 ATP.
  3. The gross yield of glycolysis is therefore
    4 ATP – 2 ATP = 2 ATP
  4. The pay-off phase also produces 2 molecules of NADH + H+ which can be further converted to a total of 5 molecules of ATP* by the electron transport chain (ETC) during oxidative phosphorylation.
  5. Thus the net yield during glycolysis is 7 molecules of ATP.

* This is calculated assuming one NADH molecule gives 2.5 molecules of ATP during oxidative phosphorylation.

References

  1. David L. Nelson and Michael M. Cox, Lehninger Principles of Biochemistry, 4th Ed.
  2. Jeremy M. Berg, John L. Tymockzo and Luber Stryer, Biochemistry, 7th Ed.

Tags: cellular respiration, electron transport chain, etc, glucose, glycolysis, metabolism, pay-off phase

Kreb’s Cycle or Citric Acid Cycle or Tricarboxylic Acid Cycle (with Animation)

By Sweety Mehta  – Sept 21, 2013  in: Animations, Biochemistry Animations, Biochemistry Notes
http://pharmaxchange.info/press/2013/09/krebs-cycle-citric-acid-cycle-tricarboxylic-acid-cycle-animation/

Introduction

Cellular respiration involves 3 stages for the breakdown of glucose – glycolysis, Kreb’s cycle and the electron transport system. The total energy produced during glucose metabolism is described at Energetics of Cellular Respiration. We have seen the glycolysis pathway with animation previously. The Kreb’s cycle is named after Adolf Krebs who studied the utilization of oxygen in a pigeon. It is also commonly known as the citric acid cycle or the tricarboxylic acid cycle. Kreb’s cycle is a very important step in the metabolic pathway as it produces about 60-70% of ATP for release of energy in the body. It directly or indirectly connects with all the other individual pathways in the body too. It takes place in the mitochondria as all the enzymes and co-enzymes required are present there.

The Kreb’s Cycle occurs in two stages:

1. Conversion of Pyruvate to Acetyl CoA

Glycolysis of 1 molecule of glucose produces 2 molecules of pyruvate. Each pyruvate in the presence of pyruvate dehydrogenase (PDH) complex in the mitochondria gets converted to acetyl CoA which in turn enters the Kreb’s cycle. This reaction is called as oxidative  decarboxylation as the carboxyl group is removed from the pyruvate molecule in the form of CO2 thus yielding 2-carbon acetyl group which along with the coenzyme A forms acetyl CoA.

The pyruvate dehydrogenase complex (PDH) comprises of three enzymes – pyruvate dehydrogenase, dihydrolipoyl transacetylase and dihydrolipoyl dehydrogenase each one playing an important role in the reaction as shown below. The PDH requires the sequential action of five co-factors or co-enzymes for the combined action of dehydrogenation and decarboxylation to take place. These five are TPP (thiamine phosphate), FAD (flavin adenine dinucleotide), NAD (nicotinamide adenine dinucleotide), coenzyme A (denoted as CoA-SH at times to depict role of -SH group) and lipoamide.

Conversion of pyruvate to acetyl CoA by the pyruvate dehydrogenase complex

pyruvate_dehydrogenase_complex_new2

Conversion of pyruvate to acetyl CoA by the pyruvate dehydrogenase complex

Pyruvate reacts with the TPP (Thiamine Phosphate) bound part of pyruvate dehydrogenase and undergoes decarboxylation to give hydroxyethyl-TPP.

This hydroxyethyl-TPP in turn gets oxidised to acetyl lipoamide by the same enzyme pyruvate dehydrogenase by the transfer of two electrons. These electrons then reduce the disulfide bond of the enzyme dihydrolipoyl transacetylase with the transfer of the acetyl group as highlighted in purple.

Dihydrolipoyl transacetylase catalyses the transesterification forming acetyl CoA by transfer of acetyl group to coenzyme A.

When acetyl CoA is being formed, at the same time reduced lipoamide is getting converted to oxidised lipoamide due to enzyme dihydrolipoyl dehydrogenase by the transfer of 2 hydrogen atoms to FAD.

Dihydrolipoyl dehydrogenase transfers the reduced equivalents (2 hydrogen atoms) to FAD thus forming FADH2. FADH2 in turn transfers a hydride ion to NAD+ to form NADH+H+.

2. Acetyl CoA Enters the Kreb’s Cycle

The acetyl CoA produced from the pyruvate dehydrogenase complex enters the Kreb’s cycle.

The animation below describes the Kreb’s cycle in detail followed by the discussion. A static image of the cycle can be found next to the discussion for reference. Press the play button to progress in the animation.

Discussion

Krebs1 cycle

The Kreb’s Cycle or Citric Acid Cycle or Tricarboxylic Acid Cycle in a static image version of the animation.

Acetyl CoA condenses with oxaloacetate (4C) to form a citrate (6C) by transferring its acetyl group in the presence of enzyme citrate synthase. The CoA liberated in this reaction is ready to participate in the oxidative decarboxylation of another molecule of pyruvate by PDH complex.

  • Citrate is then isomerised to Isocitrate by the enzyme aconitase through the formation of the intermediate cis-aconitate. This is a reversible reaction as aconitase has an iron-sulfur center which can promote reversible addition of H2O to the double bond of enzyme-bound cis-aconitate in 2 different ways, one forming citrate and the other isocitrate.
  • Isocitrate undergoes oxidative decarboxylation by the enzyme isocitrate dehydrogenase to form oxalosuccinate (intermediate- not shown) which in turn forms α-ketoglutarate (also known as oxoglutarate) which is a five carbon compound. CO2 and NADH are released in this step.
  • α-ketoglutarate (5C) undergoes oxidative decarboxylation once again to form succinyl CoA (4C) catalysed by the enzyme α-ketoglutarate dehydrogenase complex. α-ketoglutarate dehydrogenase complex is similar to PDH complex and is made up of 3 enzymes and is dependent on five co-enzymes TPP, FAD, NAD, bound lipoate and conenzyme A. In this step once again NADH and CO2 are liberated. So in all 2 molecules of NADH and 2 molecules of CO2 is produced till now.
  • Succinyl CoA is then converted to succinate by succinate thiokinase or succinyl coA synthetase in a reversible manner. This reaction involves an intermediate step in which the enzyme gets phosphorylated and then the phosphoryl group which has a high group transfer potential is transferred to GDP to form GTP. This GTP is converted to ATP by the enzyme nucleoside diphosphate kinase by donating its phosphoryl group to ADP. This reaction which involves the formation of GTP is a substrate level phosphorylation as it happens by using the energy formed by the oxidative decarboxylation of α-ketoglutarate.
  • Succinate then gets oxidised reversibly to fumarate by succinate dehydrogenase. The enzyme contains iron-sulfur clusters and covalently bound FAD which when undergoes electron exchange in the mitochondria causes the production of FADH2.
  • Fumarate is then by the enzyme fumarase converted to malate by hydration(addition of H2O) in a reversible manner.
  • Malate is then reversibly converted to oxaloacetate by malate dehydrogenase which is NAD linked and thus produces NADH.
  • The oxaloacetate produced is now ready to be utilized in the next cycle by the citrate synthase reaction and thus the equilibrium of the cycle shifts to the right.
Schrodingers_cat

Schrodingers_cat

Energetics of the Kreb’s Cycle

Keeping in mind that 1 molecule of glucose would produce 2 molecules of pyruvate via glycolysis. Hence the net energy produced by the Kreb’s cycle for each molecule of pyruvate is doubled for each molecule of glucose. Thus net energy yield in Kreb’s cycle can be summarized as follows for each molecule of glucose:

Reaction                                                              Number of ATP or                                        Number of ATP
reduced coenzyme formed                        ultimately formed

2 Pyruvate → 2 acetyl CoA                                  2 NADH                                                             5

2 Isocitrate → 2 α- ketoglutarate                     2 NADH                                                              5

2 α- ketoglutarate → 2 succinyl CoA             2 NADH                                                               5

2 Succinyl CoA → 2 succinate                           2 ATP                                                                  2

2 Succinate → 2 fumarate                               2 FADH2                                                               3

2 Malate → 2 oxaloacetate                            2 NADH                                                                  5

TOTAL                                                                                                                                                 25 ATP

* Note- This is calculated as 2.5 ATP per NADH and 1.5 ATP per FADH2. This is because there are multiple electron transport shuttle pathways through which these can be broken to ATP.

Regulation of Kreb’s Cycle

The amount of ADP and ATP largely control the citric acid cycle along with the activity of three key enzymes within the cycle:

Availability of ADP: ADP is a key substrate which finally gets converted to ATP that is essential for the energetics of the cell. A drop in ADP levels would result in inhibition of the electron transport system leading to accumulation of NADH and FADH2. These in turn inhibit the enzymes below.

Citrate Synthase: inhibited by ATP, acetyl CoA, NADH, and succinyl CoA.
Isocitrate Dehydrogenase: activated by ADP, and inhibited by NADH and ATP.
α-ketoglutarate dehydrogenase: inhibited by NADH and succinyl CoA.

Recommended Texts

David L. Nelson and Michael M. Cox, Lehninger Principles of Biochemistry 6th Edition
Jeremy M. Berg, John L. Tymockzo and Luber Stryer, Biochemistry 7th Edition

Tags: acetyl coA, animation, cellular respiration, citric acid cycle, energy, kreb’s cycle, pyruvate, pyruvate dehydrogenase, TCA cycle, tricarboxylic acid cycle

Energetics of Cellular Respiration (Glucose Metabolism)

By Sweety Mehta   – Oct 9, 2013 in: Biochemistry Notes, Notes
http://pharmaxchange.info/press/2013/10/energetics-of-cellular-respiration-glucose-metabolism/

energetics-of-cellular-respiration

electron transport chain in the mitochondrion energetics-of-cellular-respiration

Important Note: The NADH formed in the cytosol can yield variable amounts of ATP depending on the shuttle system utilized to transport them into the mitochondrial matrix. This NADH, formed in the cytosol, is impermeable to the mitochondrial inner-membrane where oxidative phosphorylation takes place. Thus to carry this NADH to the mitochondrial matrix there are special shuttle systems in the body. The most active shuttle is the malate-aspartate shuttle via which 2.5 molecules of ATP are generated for 1 NADH molecule. This shuttle is mainly used by the heart, liver and kidneys. The brain and skeletal muscles use the other shuttle known as glycerol 3-phosphate shuttle which synthesizes 1.5 molecules of ATP for 1 NADH.

Note: The above calculations are done considering that one NADH molecules produces 2.5 ATP and one FADH2 molecule produces 1.5 ATP in the ETS cycle (See full reasoning above). This is because the Kreb’s cycle occurs within the mitochondria and therefore does not require any shuttle pathway for the transport of the NADH into the mitochondrial matrix. Hence there is optimal conversion of NADH to ATP.

Development of the acetylation problem: a personal account

FRITZ LI P M A N N  Nobel Prize  1953

After my  apprenticeship with Otto Meyerhof, a first interest on my own became the phenomenon we call the Pasteur effect, this peculiar depression of the wasteful fermentation in the respiring cell. By looking for a chemical explanation of this economy measure on the cellular level, I was prompted into a study of the mechanism of pyruvic acid oxidation, since it is at the pyruvic stage where respiration branches off from fermentation. For this study I chose as a  promising system a relatively simple looking pyruvic acid oxidation enzyme in a certain strain of Lactobacillus delbrueckii1.

The most important event during this whole period, I now feel, was the accidental observation that in the L. delbrueckii system, pyruvic acid oxidation was completely dependent on the presence of inorganic phosphate. This observation was made in the course of attempts to replace oxygen by methylene blue. To measure the methylene blue reduction manometrically,
I had to switch to a bicarbonate buffer instead of the otherwise routinely used In bicarbonate, to my surprise, as shown in Fig. 1, pyruvate oxidation was very slow, but the addition of a little phosphate caused a remarkable increase in rate. The next figure, Fig. 2, shows the phosphate effect more drastically, using a preparation from which all phosphate was removed by washing with acetate buffer. Then it appeared that the reaction was really fully dependent on phosphate.

In spite of such a phosphate dependence, the phosphate balance measured by the ordinary Fiske-Subbarow procedure did not at first indicate any phosphorylative step. Nevertheless, the suspicion remained that phosphate in  some manner was entering into the reaction and that a phosphorylated intermediary was formed. As a first approximation, a coupling of this pyruvate oxidation with adenylic acid phosphorylation was attempted. And,indeed, addition of adenylic acid to the pyruvic oxidation system brought out a net  disappearance of inorganic phosphate, accounted for as adenosine triphosphate (Table 11).

I  now concluded that the missing link in the reaction chain was acetyl phosphate. In partial confirmation it was shown that a crude preparation of acetyl phosphate, synthesized by the old method of Kämmerer and Carius 2 would transfer phosphate to adenylic acid (Table 2). However, it still took quite some time from then on to identify acetyl phosphate definitely as the initial product of the pyruvic oxidation in this system3,4

At the time when these observations were made, about a dozen years ago,there was, to say the least, a tendency to believe that phosphorylation was rather specifically coupled with the glycolytic reaction. Here, however, we had found a coupling of phosphorylation with a respiratory system. This observation immediately suggested a rather sweeping biochemical significance, of transformations of electron transfer potential, respiratory or fermentative, to phosphate bond energy and therefrom to a wide range of biosynthetic reactions7.

There was a further unusual feature in this pyruvate oxidation system in that the product emerging from the process not only carried an energy-rich phosphoryl radical such as already known, but the acetyl phosphate was even more impressive through its energy-rich acetyl. It rather naturally became a contender for the role of “active” acetate, for the widespread existence of which the isotope experience had already furnished extensive evidence. I became, therefore, quite attracted by the possibility that acetyl phosphate could serve two rather different purposes, either to transfer its phosphoryl group into the phosphate pool, or to supply its active acetyl for biosynthesisof carbon structures. Thus acetyl phosphate should be able to serve as acetyldonor as well as phosphoryl donor, transferring, as shown in Fig. 3, on either side of the oxygen center, such as indicated by Bentley’s early experiments on cleavage7a of acetyl phosphate in H218O.

Phosphate dependence of pyruvate oxidation

Phosphate dependence of pyruvate oxidation

These two novel aspects of the energy problem, namely

(1) the emergence of an energy-rich phosphate bond from a purely
respiratory reaction; and

(2) the presumed derivation of a metabolic building-block through this same
reaction, prompted me to propose not only

  • the generalization of the phosphate bond as a versatie energy distributing system, but also to
    aim from there towards
  • a general concept of transfer of activated groupings by carrier as the fundamental reaction in
    biosynthesis8,9.

Although in the related manner the appearance of acetyl phosphate as a
metabolic intermediary first

  •  focused attention to possible mechanisms for the metabolic elaboration of  group activation,

it soon turned out that the relationship between acetyl phosphate and
acetyl transfer was much more complicated than anticipated.

Acetyl phosphate as acetyl and phosphoryl donor.

Although acetylation was found with rabbit liver homogenate, the
reaction was rather weak. In search of a more active system,   Pigeon
liver homogenate was tried and found to harbour an exceedingly potent
acetylation system (Ref. 11, cf. also Ref. 12). This finding of a particularly
active acetylation reaction in cell-free pigeon liver preparations was most
fortunate and played a quite important part in the development of the
acetylation problem.

[portion of lecture]

The pentose phosphate pathway is the major source for the NADPH
required for anabolic processes.
Pentose Phosphate Pathway

http://chemwiki.ucdavis.edu/Biological_Chemistry/Metabolism/Pentose_
Phosphate_Pathway

  • There are three distinct phases each of which has a distinct outcome.
  • Depending on the needs of the organism the metabolites of that outcome
    can be fed into many other pathways.
  • Gluconeogenesis is directly connected to the pentose phosphate pathway.
  • As the need for glucose-6-phosphate (the beginning metabolite in the pentose
    phosphate pathway) increases so does the activity of gluconeogenesis.

 pentose-phosphate-pathway

http://images.tutorvista.com/content/respiration/pentose-phosphate-pathway.jpeg

Introduction

The main molecule in the body that makes anabolic processes possible is NADPH.  Because of the structure of this molecule it readily donates hydrogen ions to metabolites thus reducing them and making them available for energy harvest at a later time. The PPP is the main source of synthesis for NADPH.  The pentose phosphate pathway (PPP) is also responsible for the production of Ribose-5-phosphate which is an important part of nucleic acids. Finally the PPP can also be used to produce glyceraldehyde-3-phosphate which can then be fed into the TCA and ETC cycles allowing for the harvest of energy. Depending on the needs of the cell certain enzymes can be regulated and thus increasing or decreasing the production of desired metabolites. The enzymes reasonable for catalyzing the steps of the PPP are found most abundantly in the liver (the major site of gluconeogenesis) more specifically in the cytosol. The cytosol is where fatty acid synthesis takes place which is a NADPH dependent process.

 

Oxidation Phase

  • The beginning molecule for the PPP is glucose-6-P which is the second intermediate metabolite in glycolysis. Glucose-6-P is oxidized in the presence of glucose-6-P dehydrogenase and NADP+.  This step is irreversible and is highly regulated.  NADPH and fatty acyl-CoA are strong negative inhibitors to this enzyme.  The purpose of this is to decrease production of NADPH when concentrations are high or the synthesis of fatty acids is no longer necessary.
  • The metabolic product of this step is gluconolactone which is hydrolytrically unstable.  Gluconolactonase causes gluconolactone to undergo a ring opening hydrolysis.  The product of this reaction is the more stable sugar acid, 6-phospho-D-gluconate.
  • 6-phospho-D-gluconate is oxidized by NADP+ in the presence of 6-phosphogluconate dehydrogenase which yields ribulose-5-phosphate.
  • The oxidation phase of the PPP is solely responsible for the production of the NADPH to be used in anabolic processes.

Isomerization Phase

  •  Ribulose-5-phosphate can then be isomerized by phosphopentose isomerase to produce ribose-5-phosphate.  Ribose-5-phosphate is one of the main building blocks of nucleic acids and the PPP is the primary source of production of ribose-5-phosphate.
  • If production of ribose-5-phosphate exceeds the needs of required ribose-5-phosphate in the organism, then phosphopentose epimerase catalyzes a chiralty rearrangement about the center carbon creating xylulose-5-phosphate.
  • The products of these two reactions can then be rearranged to produce many different length carbon chains.  These different length carbon chains have a variety of metabolic fates.

Rearrangement Phase 

  •  There are two main classes of enzymes responsible for the rearrangement and synthesis of the different length carbon chain molecules.  These are transketolase and transaldolase.
  • Transketolase is responsible for the cleaving of a two carbon unit from xylulose-5-P and adding that two carbon unit to ribose-5-P thus resulting in glyceraldehyde-3-P and sedoheptulose-7-P.
  • Transketolase is also responsible for the cleaving of a two carbon unit from xylulose-5-P and adding that two carbon unit to erythrose-4-P resulting in glyceraldehyde-3-P and fructose-6-P.
  • Transaldolase is responsible for cleaving the three carbon unit from sedoheptulose-7-P and adding that three carbon unit to glyceraldehyde-3-P thus resulting in erythrose-4-P and fructose-6-P.
  • The end results of the rearrangement phase is a variety of different length sugars which can be fed into many other metabolic processes.  For example, fructose-6-P is a key intermediate of glycolysis as well as glyceraldehyde-3-P.

References

  1. Garrett, H., Reginald and Charles Grisham. Biochemistry. Boston: Twayne Publishers, 2008.
  2. Raven, Peter. Biology. Boston: Twayne Publishers, 2005.

Glycogen Metabolism

Glycogen is a readily mobilized storage form of glucose. It is a very large, branched polymer of glucose residues (Figure 21.1) that can be broken down to yield glucose molecules when energy is needed. Most of the glucose residues in glycogen are linked by α-1,4-glycosidic bonds. Branches at about every tenth residue are created by α-1,6-glycosidic bonds. Recall that α-glycosidic linkages form open helical polymers, whereas β linkages produce nearly straight strands that form structural fibrils, as in cellulose (Section 11.2.3).

http://www.ncbi.nlm.nih.gov/books/NBK21190/bin/ch21f1.jpg

Figure 21.1

Glycogen Structure ch21f1

Glycogen Structure. In this structure of two outer branches of a glycogen molecule, the residues at the nonreducing ends are shown in red and residue that starts a branch is shown in green. The rest of the glycogen molecule is represented by R.

Glycogen is not as reduced as fatty acids are and consequently not as energy rich. Why do animals store any energy as glycogen? Why not convert all excess fuel into fatty acids? Glycogen is an important fuel reserve for several reasons. The controlled breakdown of glycogen and release of glucose increase the amount of glucose that is available between meals. Hence, glycogen serves as a buffer to maintain blood-glucose levels. Glycogen’s role in maintaining blood-glucose levels is especially important because glucose is virtually the only fuel used by the brain, except during prolonged starvation. Moreover, the glucose from glycogen is readily mobilized and is therefore a good source of energy for sudden, strenuous activity. Unlike fatty acids, the released glucose can provide energy in the absence of oxygen and can thus supply energy for anaerobic activity.

Gluconeogenesis
ChemWiki: The Dynamic Chemistry E-textbook > Biological Chemistry > Metabolism > Gluconeogenesis

Gluconeogenesis is much like glycolysis only the process occurs in reverse. However, there are exceptions. In glycolysis there are three highly exergonic steps (steps 1,3,10). These are also regulatory steps which include the enzymes hexokinase, phosphofructokinase, and pyruvate kinase. Biological reactions can occur in both the forward and reverse direction. If the reaction occurs in the reverse direction the energy normally released in that reaction is now required. If gluconeogenesis were to simply occur in reverse the reaction would require too much energy to be profitable to that particular organism. In order to overcome this problem, nature has evolved three other enzymes to replace the glycolysis enzymes hexokinase, phosphofructokinase, and pyruvate kinase when going through the process of gluconeogenesis:

  1. The first step in gluconeogenesis is the conversion of pyruvate to phosphoenolpyruvic acid (PEP). In order to convert pyruvate to PEP there are several steps and several enzymes required. Pyruvate carboxylase, PEP carboxykinase and malate dehydrogenase are the three enzymes responsible for this conversion. Pyruvate carboxylase is found on the mitochondria and converts pyruvate into oxaloacetate. Because oxaloacetate cannot pass through the mitochondria membranes it must be first converted into malate by malate dehydrogenase. Malate can then cross the mitochondria membrane into the cytoplasm where it is then converted back into oxaloacetate with another malate dehydrogenase. Lastly, oxaloacetate is converted into PEP via PEP carboxykinase. The next several steps are exactly the same as glycolysis only the process is in reverse.
  2. The second step that differs from glycolysis is the conversion of fructose-1,6-bP to fructose-6-P with the use of the enzyme fructose-1,6-phosphatase. The conversion of fructose-6-P to glucose-6-P uses the same enzyme as glycolysis, phosphoglucoisomerase.
  3. The last step that differs from glycolysis is the conversion of glucose-6-P to glucose with the enzyme glucose-6-phosphatase. This enzyme is located in the endoplasmic reticulum.

Glycolysis

File:Glycolysis overview.svg

Regulation

Because it is important for organisms to conserve energy, they have derived ways to regulate those metabolic pathways that require and release the most energy. In glycolysis and gluconeogenesis seven of the ten steps occur at or near equilibrium. In gluconeogenesis the conversion of pyruvate to PEP, the conversion of fructose-1,6-bP, and the conversion of glucose-6-P to glucose all occur very spontaneously which is why these processes are highly regulated. It is important for the organism to conserve as much energy as possible. When there is an excess of energy available, gluconeogenesis is inhibited. When energy is required, gluconeogenesis is activated.

  1. The conversion of pyruvate to PEP is regulated by acetyl-CoA. More specifically pyruvate carboxylase is activated by acetyl-CoA. Because acetyl-CoA is an important metabolite in the TCA cycle which produces a lot of energy, when concentrations of acetyl-CoA are high organisms use pyruvate carboxylase to channel pyruvate away from the TCA cycle. If the organism does not need more energy, then it is best to divert those metabolites towards storage or other necessary processes.
  2. The conversion of fructose-1,6-bP to fructose-6-P with the use of fructose-1,6-phosphatase is negatively regulated and inhibited by the molecules AMP and fructose-2,6-bP. These are reciprocal regulators to glycolysis’ phosphofructokinase. Phosphofructosekinase is positively regulated by AMP and fructose-2,6-bP. Once again, when the energy levels produced are higher than needed, i.e. a large ATP to AMP ratio, the organism increases gluconeogenesis and decreases glycolysis. The opposite also applies when energy levels are lower than needed, i.e. a low ATP to AMP ratio, the organism increases glycolysis and decreases gluconeogenesis.
  3. The conversion of glucose-6-P to glucose with use of glucose-6-phosphatase is controlled by substrate level regulation. The metabolite responsible for this type of regulation is glucose-6-P. As levels of glucose-6-P increase, glucose-6-phosphatase increases activity and more glucose is produced. Thus glycolysis is unable to proceed.

 

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Pathology Emergence in the 21st Century

Author and Curator: Larry Bernstein, MD, FCAP 

 

This discussion follows the series on DNA and its replication, the code of life, and immediately follows a an up to date survey of RNA, it’s many discovered forms, their function, and the transcription of RNA, intermediate to protein synthesis.  This will comprise a series of articles, including the chemistry, structure, and function of proteins, before turning to the “metabolome”.  This discussion is about the development of the scientific profession of pathology in three notable phases.  The first phase might be considered the gross anatomical discussion developed in Vienna, under Rokitansky, whose greatest student was the Hungarian pathologist, Semelweis, who began the insistence on handwashing prior to visiting the delivery room based on the observation that deliver was safer done by midwifes than by physicians.  This was prior to the great discoveries in microbiology.  The Rokitansky procedure is distinctive in removing organ systems in order to examine postmortem anatomical changes.  His document on the pathology of the organs was monumental.  It was refined by Rudolf Virchow, who removed one organ at a time, but he also had the now developing field of microscopic anatomy (also describing leukemia),

 

chart1  lymphoma_leukemia

 

Rudolph Virchow  1821-1902

Rudolph Virchow 1821-1902

 

 

 

 

 

 

 

that would also be embellished by a generation of histologists who introduced staining techniques.  The most remarkable anatomist to emerge in that period was John Hunter, the Scottish born anatomist and surgeon in London, who taught medical students from England and United States, and who was the physician for Sir David Hume.  When he served in the 30 years war, he pulled wounded soldiers out of the mud to a clearing to care for their wounds.

The 20th century saw the introduction of a new medical school education system under advisement by the Carnegie Commission. [Abraham Flexner Report]  This led to the teaching of basic sciences of anatomy, physiology, pharmacology, pathology, and later genetics and microbiology as prerequisite to clinical teaching.  Moreover, teaching was done by formal systems of disease, which later developed into rotations in Obstetrics and Gynecology, Medicine, and Surgery, Pediatrics, to which endocrinology and neurology and psychiatry were added.  The first great Medical School was actually Johns Hopkins, that paved the groundwork.  Harvard, Cornell, Columbia, and NYU followed, as did the University of California, San Francisco, and the University of Chicago.  This was a period dominated by many important discoveries, and a domination of the Nobel Prizes in Medicine and Physiology, Chemistry and Physics (rivalled only by Germany and United Kingdom).  The Uniqueness of Pathology lies in its placement in the first year of medical school, in preparation for the formal study of medicine, with a foot in both basic sciences and the other in clinical practice.  The pathologist received all tissues removed from surgical procedures, and performed autopsies to determine the cause of death and comorbid conditions.   The development of a substantial knowledge of the kidney gave rise to the specialty of nephrology, and at the same time drew pathologists into a “phase” of molecular biology with the introduction of the electron microscope.  However, the field of immunology developed, and the need for transfusion hastened the emergence of clinical antigen-antibody testing, the crossmatch, blood banking, and later, the emergence of organ transplantation.  In addition, clinical microbiology became a part of clinical pathology, and included fungi and tick-borne diseases, and nemitodes.

We have entered the third phase of pathology with the completion of the human genetic code, and with the development of target pharmaceutical development in the 21st century.

 

Modern Techniques of Molecular Pathology

A look at clinical laboratory science and its expected progress over the next decade

 

Molecular Diagnostics    2013; 22 (2), p 35Promising forecasts project great expectations for medical sciences in the year 2013 and beyond. These predictions follow a decade after completion of the Human Genome Project, and are accompanied by immense breakthroughs in computational and applied mathematics. In my view, they are:

  • Genomic and allied -omics technology
  • Innovation in mathematical classification (complexity)
  • Nanotechnology
  • Synthetic chemistry from physics, organic and inorganic chemistry

It is not my intention to go deeply into the exponential group of these advanced and integrative sciences; rather, I want to raise awareness of an emerging new world that will open to the clinical laboratory scientist, and signal the need in the next generation of laboratory personnel to embrace knowledge domains that will be critical for their careers.

All of these breakthroughs are tied together by a search for personalized and integrative medicine. These breakthroughs will reinvent nutritional and pharmaceutical medicine as well as medical devices and restructure clinical laboratory and imaging applications to cardiology, oncology, radiology and anatomical pathology.

Metabolomics

What does metabolomics and metabolic profiling have to do with this? Metabolomics is the measurement of small molecules that interact with membrane receptors1 that are involved with regulation of genomic transcription and cellular regulation and upregulation or downregulation of metabolic processes essential to health. As well, these small molecules may provide targets for disease treatments, and as they are investigated, also provide further “analytes for diagnosis and, moreover, prediction of short-term or long-term outcomes.”2

As a result, the laboratory will become a more significant factor in measuring health and disease and in guiding health or disease maintenance. As our population has reached increased age limits, the laboratory has been a contributor in the public health sphere, and will have a greater role as a result of:

  • Improved tie in with provision of information to not only the healthcare workers, but also the patient
  • Achieve turnaround times for critical results through better workflow
  • Greater control and access to a next generation of point-of-care technology integrated with the laboratory database, and a restructured electronic health record

Despite the hype about the “big data” revolution, this is achievable in the system proposed because there is a published model to achieve this.2

Familiar Methods

Either individually or grouped as a profile, metabolites are detected by nuclear magnetic resonance spectroscopy or mass spectrometry, providing a basis for uses of ­metabolome findings extended to the early detection and diagnosis of cancer and as both a predictive and pharmacodynamics marker of drug effect. We can expect it to become the link between the laboratory and the clinic. The methods used in genomics are microarrays, and for proteomics they are the already familiar chromatographic principles that species migrate at different rates through a column matrix based on their volatility, or carries out a separation as the molecules differ by their adsorption to and elution from a solid matrix, dependent on the binding to the matrix and solubility in the solvent eluate, modified by pH, ionic concentration, and specific conditions needed for recovery. Powerful mathematical tools are used to analyze the data.3

Cardiovascular Disease

Although coronary thrombosis is the final event in acute coronary syndromes, increasing evidence suggests that inflammation also plays a key role in development of atherosclerosis and its clinical manifestations, such as myocardial infarction, stroke and peripheral vascular disease. The inflammatory component was indicated by epidemiological studies of elevated serum levels of high sensitivity C-reactive protein. That eventually led to the demonstration of a benefit from reduction of CRP in individuals without ­characteristic lipidemia in a major clinical trial, which drew a relationship between diabetes, obesity and disordered inflammatory response in the causation of coronary artery disease, aortic valve and artery disease, carotid artery and peripheral vascular disease.

Cancer

Because cancer cells are known to possess a highly unique metabolic phenotype, development of specific biomarkers in oncology is possible and might be used in identifying fingerprints, profiles or signatures to detect the presence of cancer, determine prognosis and/or assess the pharmacodynamic effects of therapy.4

HDM2, a negative regulator of the tumor suppressor p53, is over-expressed in many cancers that retain wild-type p53. Consequently, the effectiveness of chemotherapies that induce p53 might be limited, and inhibitors of the HDM2-p53 interaction are being sought as tumor-selective drugs.5

Coagulation

Blood coagulation plays a key role among numerous mediating systems activated in inflammation. Receptors of the PAR family serve as sensors of serine proteinases of the blood clotting system in the target cells involved in inflammation. Activation of PAR_1 by thrombin and of PAR_2 by factor Xa leads to a rapid expression and exposure on the membrane of endothelial cells of both adhesive proteins that mediate an acute inflammatory reaction and of the tissue factor that initiates the blood coagulation cascade.

The details of evolving methods are avoided in order to build the argument that a very rapid expansion of discovery has been evolving depicting disease, disease mechanisms, disease associations, metabolic biomarkers, study of effects of diet and diet modification, and opportunities for targeted drug development.

  1. Bernstein is CEO of Triplex Medical Science and CSO of Leaders in Pharmaceutical Intelligence. He has been involved in a collaborative project on reducing the noise that exists in complex data and developing a primary evidence-based classification since retiring from a career in pathology supning four decades.

References

1. Bernstein LH. Metabolomics, metabonomics and functional nutrition: The next step in nutritional metabolism and biotherapeutics. Journal of Pharmacy and Nutrition Sciences, 2012;2.

2. David G, Bernstein LH, Coifman RR. Generating evidence-based interpretation of hematology screens via anomaly characterization. The Open Clinical Chemistry Journal 2011;4: 10-16.

3. Grainger DJ. Megavariate statistics meets high data-density analytical methods: The future of medical diagnostics? IRTL Reviews 2003;1:1-6.

4. Spratlin JL, Serkova NJ, Eckhardt SG. Clinical applications of metabolomics in oncology: A review. Clin Cancer Res 2009;15; 15(2): 431-440.

5. Fischer PM, Lane DP. Small molecule inhibitors of thep53 suppressor HDM2: Have protein-protein interactions come of age as drug targets? Trends in Pharm Sci 2004;25(7):343-346.

Directions for Genomics in Personalized Medicine

Author: Larry H. Bernstein, MD, FCAP

Purpose

This discussion will identify the huge expansion of genomic technology in the search for  biopharmacotherapeutic targets that continue to be explored involving different levels and interacting signaling pathways.   There are several methods of analyzing gene expression that will be discussed. Great primary emphasis required investigation of combinations of mutations expressed in different cancer types.

 

James Watson has proposed a major hypothesis that expresses the need to focus on “central” “driver mutations” that correspond with the regulation of gene expression, cell proliferation, and cell metabolism with a critical rejection of antioxidant benefits.  What hasn’t been know is why drug resistance develops and whether the cellular migration and aerobic glycolysis can be redirected after cell metastasis occurs.  I attempt to bring out the complexities of current efforts.

 

Introduction

  • This discussion is a continuation of a previous discussion on the role of genomics if discovery of therapeutic targets for cancer, each somewhat different, but all related to:
  • The reversal of carcinoma by targeting a key driver of multiple signaling pathways that activate cell proliferation
  • Pinpointing a stage in a multistage process at which tumor progression links to changes in morphology from basal cells to invasive carcinoma with changes in polarity and loss of glandular architecture
  • Reversal of the carcinoma through using a small molecule that either is covalently bound to a nanoparticle delivery system that blocks or reverses tumor development
  • Synthesis of a small molecule that interacts with the translation of the genome either by substitution of a key driver molecule or by blocking at the mRNA stage of translation
  • Blocking more than one signaling pathway that are links to carcinogenesis and cellular proliferation and invasion

Difficulty of the problem

A problem expressed by James Watson is that the investigations that are ongoing

  • are following a pathway that is not driven by attacking the “primary” driver of carcinogenesis.

He uses the Myc gene as an example, as noted in the previous discussion. The problem may be more complicated than he envisions.

  • The most consistent problem in chemotherapy, irrespective of the design and the target has been cancer remission for a short time followed by recurrence, and then
  • switching to another drug, or combination chemotherapy.

It is common to “clean” the field at the time of resection using radiotherapy before chemotherapy.

  • But the goal is understood to be “palliation”, not cure.

This raises a serious issue in the hypothesis posed by Watson. The issue is

  • whether there is a core locus of genetic regulation that is common to carcinogenesis irrespective of tissue metabolic expression.
  • This is supported by the observation that tissue specific expression is lost in cancer cells by de-differentiation.

Historical Perspective

AEROBIC GLYCOLYSIS

In 1967 Otto Warburg published his view in a paper “The prime cause and prevention of cancer”.
There are primary and secondary causes of all diseases

  • plague – primary: plague bacillus
  • plague – secondary: filth, rats, and fleas

Otto Heinrich Warburg (1883-  )

 

 

 

 

 

 

Otto Heinrich Warburg (Photo credit: Wikipedia)

 

cancer, above all diseases,

  • has countless seconday causes
  • primary – replacement of respiration of oxygen in normal body tissue by fermentation of glucose with conversion from obligate aerobic to anaerobic, as in bacterial cells

The cornerstone to understanding cancer is in study of the energetics of life

This thinking came out of decades of work in the Dahlem Institute Kaiser Wilhelm pre WWII and Max Planck Institute after WWII, supported by the Rockefeller Foundation.

  • The oxygen- and hydrogen-transferring enzymes were discovered and isolated.
  • The methods were elegant for that time, using a manometer that improved on the method used by Haldane, that did not allow the leakage of O2 or CO2.
  • The interest was initiated by the increased growth of Sea Urchin eggs after fertization, which turned out to be not comparable to the rapid growth of cancer cells.
  • Warburg used both normal and cancer tissue and measured the utilization of O2. He found
    • that the normal tissue did not accumulate lactic acid.
    • Cancer tissue generated lactic acid
    • the rate of O2 consumption the same as normal tissue, but
    • the rate of lactate formation far exceeded any tissue, except the retina.
    • This was a discovery studied by “Pasteur” 60 years earlier (facultative aerobes), which he called thePasteur effect.
    • Hematopoietic cells of bone marrow develop aerobic glycolysis when exposed to a low oxygen condition.

He then followed on an observation by Otto Meyerhoff (Embden-Myerhoff cycle) that in muscle

  • the consumption of one molecule of oxygen generates two molecules of lactate, but in aerobic glycolysis, the relationship disappears.
  • He expressed the effectiveness of respiration by the ‘Meyerhoff quotient’.
  • He found that cancer cells didn’t have a quotient of ’2′

The role of the allosteric enzyme phosphofructokinase (PFK) not then known, would tie together the glycolytic and gluconeogenic pathways.
He used a heavy metal ion chelator ethylcarbylamine to

  • sever the link and turn on aerobic glycolysis.

The explanation for this was provided years later by the work fleshed out by Lynen, Bucher, Lowry, Racker, and Sols.

  • The rate-limiting enzyme, PFK is regulated by the concentrations of ATP, ADP, and inorganic phosphate. The ethylcarbylamide was an ‘uncoupler’ of oxidative phosphorylation.

Warburg understood that when normal cells switched to aerobic glycolysis

  • it is a re-orientation of normal cell expression.
  • this provides the basis for the inference that neoplastic cells become more like each other than their cell of origin.
  • embryonic cells can be transformed into cancer cells under hypoxic conditions
  • re-exposure to higher oxygen did not cause reversion back to normal cells.

Warburg publically expressed the rejected view in 1954 (at age 83) that restriction of chemical wastes, food additives, and air pollution would substantially reduce cancer rates.

His emphasis on the impairment of respiration was inadequate.

  • the prevailing view today is loss of controlled growth of normal cells in cancer cells.

Otto Warburg: Cell Physiologist, Biochemist, and Eccentric. Hans Krebs, in collaboration with Roswitha Schmid. Clarendon Press, Oxford. 1991.ISBN 0-19-858171-8.

 

A multiphoton fluorescence microscope (MFM) is a specialized optical microscope.

The MFM uses pulsed long-wavelength light to excite fluorophores within the specimen being observed. The fluorophore absorbs the energy from two long-wavelength photons which must arrive simultaneously in order to excite an electron into a higher energy state, from which it can decay, emitting a fluorescence signal. It differs from traditional fluorescence microscopy in which the excitation wavelength is shorter than the emission wavelength, as the summed energies of two long-wavelength exciting photons will produce an emission wavelength shorter than the excitation wavelength.[1]

Multiphoton fluorescence microscopy has similarities to confocal laser scanning microscopy. Both use focused laser beams scanned in a raster pattern to generate images, and both have an optical sectioning effect. Unlike confocal microscopes, multiphoton microscopes do not contain pinhole apertures, which give confocal microscopes their optical sectioning quality. The optical sectioning produced by multiphoton microscopes is a result of the point spread function formed where the pulsed laser beams coincide. The multiphoton point spread function is typically dumbbell-shaped (longer in the x-y plane), compared to the upright rugby-ball shaped point spread function of confocal microscopes. However, in many interesting cases the shape of the spot and its size can be designed to realize specific desired goals.[2]

The longer wavelength, low energy (typically infra-red) excitation lasers of multiphoton microscopes are well-suited to use in imaging live cells as they cause less damage than short-wavelength lasers, so cells may be observed for longer periods with fewer toxic effects. Many researchers are currently working toward better and higher resolution multiphoton imaging developments.

Two-photon excitation microscopy is a fluorescence imaging technique that allows imaging of living tissue up to a very high depth, up to about one millimeter. Being a special variant of the multiphoton fluorescence microscope, it uses red-shifted excitation light which can also excite fluorescent dyes. However, for each excitation, two photons of infrared light are absorbed. Using infrared light minimizes scattering in the tissue. Due to the multiphoton absorption, the background signal is strongly suppressed. Both effects lead to an increased penetration depth for these microscopes. Two-photon excitation can be a superior alternative to confocal microscopy due to its deeper tissue penetration, efficient light detection, and reduced phototoxicity.[1]

Two-photon excitation employs two-photon absorption, a concept first described by Maria Goeppert-Mayer (1906–1972) in her doctoral dissertation in 1931,[2] and first observed in 1961 in a CaF2:Eu2+ crystal using laser excitation by Wolfgang Kaiser.[3] Isaac Abella showed in 1962 in cesium vapor that two-photon excitation of single atoms is possible.[4]

The concept of two-photon excitation is based on the idea that two photons of comparably lower energy than needed for one photon excitation can also excite a fluorophore in one quantum event. Each photon carries approximately half the energy necessary to excite the molecule. An excitation results in the subsequent emission of a fluorescence photon, typically at a higher energy than either of the two excitatory photons. The probability of the near-simultaneous absorption of two photons is extremely low. Therefore a high flux of excitation photons is typically required, usually from a femtosecond laser. The purpose of employing the two-photon effect is that the axial spread of the point-spread-function is substantially lower than for single-photon excitation. As a result, the resolution along the z dimension is improved, allowing for thin optical sections to be cut. In addition, in many interesting cases the shape of the spot and its size can be designed to realize specific desired goals.[5] Two-photon microscopes are less damaging to the sample than a single-photon confocal microscope.

The most commonly used fluorophores have excitation spectra in the 400–500 nm range, whereas the laser used to excite the two-photon fluorescence lies in the ~700–1000 nm (infrared) range. If the fluorophore absorbs two infrared photons simultaneously, it will absorb enough energy to be raised into the excited state. The fluorophore will then emit a single photon with a wavelength that depends on the type of fluorophore used (typically in the visible spectrum). Because two photons are absorbed during the excitation of the fluorophore, the probability for fluorescent emission from the fluorophores increases quadratically with the excitation intensity. Therefore, much more two-photon fluorescence is generated where the laser beam is tightly focused than where it is more diffuse. Effectively, excitation is restricted to the tiny focal volume (~1 femtoliter), resulting in a high degree of rejection of out-of-focus objects. This localization of excitation is the key advantage compared to single-photon excitation microscopes, which need to employ additional elements such as pinholes to reject out-of-focus fluorescence. The fluorescence from the sample is then collected by a high-sensitivity detector, such as a photomultiplier tube. This observed light intensity becomes one pixel in the eventual image; the focal point is scanned throughout a desired region of the sample to form all the pixels of the image. The scan head is typically composed of two mirrors, the angles of which can be rapidly altered with a galvanometer.

.Multiphoton microscopy: a potential “optical biopsy” tool for real-time evaluation of lung tumors without the need for exogenous contrast agents.

 

Jain M1, Narula N, Aggarwal A, Stiles B, Shevchuk MM, Sterling J, Salamoon B, Chandel V, Webb WW, Altorki NK, Mukherjee S.
From the Departments of Urology (Dr Jain), Pathology and Laboratory Medicine (Drs Narula and Shevchuk), Biochemistry (Drs Aggarwal and Mukherjee, Mr Sterling, and Mr Salamoon), Thoracic Surgery (Drs Stiles and Altorki), and Surgery (Mr Chandel), Weill Cornell Medical College, New York, New York; and the School of Applied and Engineering Physics, Cornell University, Ithaca, New York (Dr Webb). Dr Aggarwal is now with the Department of Science, Borough of Manhattan Community College, New York.
Arch Pathol Lab Med. 2014 Aug;138(8):1037-47.   http://dx.doi.org:/10.5858/arpa.2013-0122-OA. Epub 2013 Nov 7

Context.-Multiphoton microscopy (MPM) is an emerging, nonlinear, optical-biopsy technique, which can generate subcellular-resolution images from unprocessed and unstained tissue in real time.

Objective.-To assess the potential of MPM for lung tumor diagnosis. Design.-Fresh sections from tumor and adjacent nonneoplastic lung were imaged with MPM and then compared with corresponding hematoxylin-eosin slides.

Results.-Alveoli, bronchi, blood vessels, pleura, smokers’ macrophages, and lymphocytes were readily identified with MPM in nonneoplastic tissue. Atypical adenomatous hyperplasia (a preinvasive lesion) was identified in tissue adjacent to the tumor in one case. Of the 25 tumor specimens used for blinded pathologic diagnosis, 23 were diagnosable with MPM. Of these 23 cases, all but one adenocarcinoma (15 of 16; 94%) was correctly diagnosed on MPM, along with their histologic patterns. For squamous cell carcinoma, 4 of 7 specimens (57%) were correctly diagnosed. For the remaining 3 squamous cell carcinoma specimens, the solid pattern was correctly diagnosed in 2 additional cases (29%), but it was not possible to distinguish the squamous cell carcinoma from adenocarcinoma. The other squamous cell carcinoma specimen (1 of 7; 14%) was misdiagnosed as adenocarcinoma because of pseudogland formation. Invasive adenocarcinomas with acinar and solid pattern showed statistically significant increases in collagen. Interobserver agreement for collagen quantification (among 3 observers) was 80%.

Conclusions.-Our pilot study provides a proof of principle that MPM can differentiate neoplastic from nonneoplastic lung tissue and identify tumor subtypes. If confirmed in a future, larger study, we foresee real-time intraoperative applications of MPM, using miniaturized instruments for directing lung biopsies, assessing their adequacy for subsequent histopathologic analysis or banking, and evaluating surgical margins in limited lung resections. PMID: 24199831

Lung cancer is the most common cause of cancer-related mortality worldwide in both men and women, with 226 160 new cases and 160 340 deaths estimated in the United States alone in 2012.1 Lung tumors are currently detected on chest radiography and computed tomography imaging, but definitive diagnosis, especially distinguishing the various subtypes of lung cancer, requires cytologic or histopathologic examination. Although considered the gold standard in establishing diagnosis, histopathology requires time-consuming tissue processing and can sometimes require repeat biopsies if the initial specimen was nondiagnostic. To overcome some of the obstacles associated with histopathologic processing, efforts have been made to develop high-resolution “optical biopsy” imaging techniques.

In this proof-of-principle pilot study, we explored the use of multiphoton microscopy (MPM) as a promising, new optical biopsy tool for the detection and diagnosis of lung tumors in real time.

Multiphoton microscopy relies on the simultaneous absorption of 2 or 3 low-energy (near-infrared) photons to cause a nonlinear excitation, equivalent to that created by a single photon of shorter wavelength light. By using 2-photon excitation in the 700- to 800-nm range, MPM enables both in vivo and ex vivo imaging of fresh, unprocessed, and unstained tissue at histologic resolution via generating intrinsic tissue emissions. Intrinsic tissue emission signals used in this study included autofluorescence and second harmonic generation (SHG).2–4

Twenty-five adult subjects diagnosed with lung cancer and undergoing lobectomies at our institution participated in this Institutional Review Board–approved study.

An Olympus FluoView FV1000MPE imaging system (Olympus America, Center Valley, Pennsylvania) was used for all MPM imaging. For detailed description of MPM imaging conditions, please see Supplementary Methods (supplemental digital content for this article is available at www.archivesofpathology.org in the August 2014 table of contents). Briefly, fresh (unprocessed and unstained) specimens were excited using 780 nm light from a tunable titanium-sapphire laser (Mai Tai DeepSee, Spectra-Physics, Irvine, California). Three distinct intrinsic tissue-emission signals were collected using photomultiplier tubes and were then color coded by using MetaMorph (version 7.0, revision 4, Molecular Devices, Sunnyvale, California) as follows: (1) SHG (360–400 nm, color-coded red), a nonlinear scattering signal originating from tissue collagen; (2) short wavelength autofluorescence (420–490 nm, color-coded green), originating in part from reduced nicotinamide adenine dinucleotide and flavin adenine dinucleotide in normal epithelial, neoplastic, and inflammatory cells, and from elastin in the alveolar septa; and (3) long wavelength autofluorescence (550–650 nm, color-coded blue), originating in part from carbon-laden macrophages.

Arch Path MPM

Arch Path MPM

http://www.archivesofpathology.org/na101/home/literatum/publisher/pinnacle/journals/content/arpa/2014/15432165-138.8/arpa.2013-0122-oa/20140721/images/medium/i1543-2165-138-8-1037-f01.gif

http://www.archivesofpathology.org/na101/home/literatum/publisher/pinnacle/journals/content/arpa/2014/15432165-138.8/arpa.2013-0122-oa/20140721/images/large/i1543-2165-138-8-1037-f01.jpeg

Figure 1. Comparative multiphoton microscopy (MPM) and hematoxylin-eosin images of nonneoplastic and smoker lung. A and B, Low-magnification images show lung parenchyma composed of alveoli (arrows) surrounded by pleura (arrowheads). Inset in MPM shows pleura with collagen (red) and elastin (green) components. C and D, High-magnification images show primarily elastin fibers, with some collagen in the septal wall (arrowheads) of the alveoli (arrows). E and F, Low-magnification images show bronchus (*) with cartilage (arrowheads) and a medium-sized blood vessel (arrows). G and H, High-magnification images show columnar lining of the bronchus (arrows) and underlying connective tissue (arrowheads). I and J, Alveoli filled with carbon-laden macrophages (arrows; blue in MPM) and noncarbon-laden macrophages (arrowheads; green in MPM). K and L, A collection of small lymphocytes (arrowheads and inset), along with smoker’s macrophages (arrows). Some loss and thickening of the alveolar septa is shown (I through L) (MPM, original magnifications ×48 [A and E], ×96 [A inset], ×300 [C, G, I, and K], ×600 [K inset]; hematoxylin-eosin, original magnifications ×40 [B, F] and ×200 [D, H, J, and L]).

To assess the diagnostic potential of MPM, a blinded analysis was conducted. The attending pulmonary pathologist and an attending general surgical pathologist first familiarized themselves to the histologic features seen on MPM images in both nonneoplastic and neoplastic (adenocarcinoma and squamous cell carcinoma [SCC]) lung tissue. Because, in our study, multiple images were acquired from different areas of a given tumor, we used some of those images for the training set and did not include them in the blinded test set. Subsequently, test MPM images from all lung tumor specimens were assessed in a blinded fashion and were categorized according to subtype and pattern using the routine histopathologic criteria.9,10 These diagnoses were then correlated with diagnoses made by the same pathologist, based on the corresponding H&E sections prepared from the same specimens.

Visualizing Lung From Smoker With MPM
Using MPM to Identify Invasive and Preinvasive Adenocarcinoma

Figure 2, A through B, shows an example of a lesion with atypical adenomatous hyperplasia, which was an incidental finding on MPM in “tumor-free” lung tissue. It shows the proliferation of atypical pneumocytes, along the preexisting alveolar wall. Gaps between the cells (discontinuous layer of pneumocytes) support the diagnosis of atypical adenomatous hyperplasia. Adenocarcinoma of lung with lepidic-predominant pattern, in contrast, shows continuous proliferation of tumor cells along the alveolar wall.

Arch Path  progression from atypical lesion to invasive adenocarcinoma

Arch Path progression from atypical lesion to invasive adenocarcinoma

Figure 2. Comparative multiphoton microscopy and hematoxylin-eosin images showing progression from atypical lesion to various patterns of invasive adenocarcinoma of lung. A and B, Images of atypical adenomatous hyperplasia shows a focus of pneumocyte proliferation (cuboidal cells with gaps between them) along the alveolar wall (arrows and insets). C and D, Images of adenocarcinoma of lung with lepidic-predominant pattern (arrows) and a few clusters of free-floating tumor cells (arrowheads). E and F, Images of adenocarcinoma of lung with acinar-predominant pattern (arrows). G and H, Images showing solid pattern (arrows) with suggestion of gland formation (arrowheads). I and J, Images showing papillary pattern (papillae with fibrovascular core; arrows). K and L, Images showing micropapillary pattern, with complete destruction of normal lung parenchyma. The airspace shows small papillary clusters of tumor cells (arrows) lacking true fibrovascular cores (multiphoton microscopy, original magnifications ×300 [A, C, E, G, I, and K] and ×600 [inset]; hematoxylin-eosin, originalmagnifications ×200 [B, D, F, H, J, and L] ×400 [inset]).

Arch Path SCC

Arch Path SCC

http://www.archivesofpathology.org/na101/home/literatum/publisher/pinnacle/journals/content/arpa/2014/15432165-138.8/arpa.2013-0122-oa/20140721/images/medium/i1543-2165-138-8-1037-f02.gif

http://www.archivesofpathology.org/na101/home/literatum/publisher/pinnacle/journals/content/arpa/2014/15432165-138.8/arpa.2013-0122-oa/20140721/images/large/i1543-2165-138-8-1037-f02.jpeg

Adenocarcinoma with a papillary-predominant pattern shows clear papillary projections composed of cuboidal to columnar cells, which line collagen-rich fibrovascular cores (Figure 2, I and J). Micropapillary adenocarcinoma, on the other hand, shows small papillary clusters of malignant cells within the airspace, with no true fibrovascular cores (Figure 2, K and L).

Using MPM to Identify SCC of Lung

Figure 3 shows high-magnification images acquired from the tumor mass in subjects with a diagnosis of SCC. Figure 3, A and B, shows sheets of malignant cells with a complete loss of the normal architecture of the lung parenchyma. These cells are seen as arranged in a pavementlike fashion with a high nuclear to cytoplasmic ratio (indicating a high-grade tumor). Pavementlike arrangement of cells is a characteristic of SCC that helps to differentiate it from the solid-predominant pattern of adenocarcinoma. We also observed an increased amount of stroma and mononuclear inflammatory cells surrounding the tumor (Figure 3, A, inset). These mononuclear inflammatory cells were confirmed as lymphocytes on H&E. This case was correctly diagnosed as SCC on MPM. Figure 3, C and D, shows images from the tumor mass of another subject, also diagnosed with SCC on H&E. However, it was misdiagnosed as adenocarcinoma on MPM, primarily because the central necrosis in the tumor nest was interpreted as gland formation. When the images were reanalyzed with knowledge of the SCC diagnosis, the pavementlike arrangement of cells was identified. We thus expect that, with a larger sample of SCC specimens and more experience, our ability to correctly diagnose SCC will improve significantly. Also, in the future, any specimen with a likely SCC diagnosis will be imaged over a larger area by using image tiling and by taking multiple stacks from various areas in the lesion, so as not to be misled by occasional, spurious, histologic features.

Figure 3. Comparative multiphoton microscopy and hematoxylin-eosin images of squamous cell carcinoma of the lung. A and B, Images of squamous cell carcinoma (SCC) of the lung showing sheets of malignant cells with high nuclear to cytoplasmic ratio (arrows), surrounded by lymphocytes (arrowheads) interspersed in collagen bundles (inset). C and D, Images of SCC of the lung showing pavementlike arrangement of the cells (arrows). Also shown is a nest of squamous cells with focal necrosis (arrowheads) forming pseudoglands, leading to a misdiagnosis of adenocarcinoma (multiphoton microscopy, original magnifications ×300 [A and C] and ×600 [inset]; hematoxylin-eosin, original magnifications ×200 [B and D]).

http://www.archivesofpathology.org/na101/home/literatum/publisher/pinnacle/journals/content/arpa/2014/15432165-138.8/arpa.2013-0122-oa/20140721/images/medium/i1543-2165-138-8-1037-f03.gif

http://www.archivesofpathology.org/na101/home/literatum/publisher/pinnacle/journals/content/arpa/2014/15432165-138.8/arpa.2013-0122-oa/20140721/images/large/i1543-2165-138-8-1037-f03.jpeg

Using MPM to Assess the Degree of Collagen in Lung Carcinoma

Previous studies have reported the amount of collagen as a prognostic factor in small, peripheral lung adenocarcinomas5,6,8 and SCCs.7 In our study, we categorized adenocarcinomas into 3 groups:

(1) well-differentiated, adenocarcinomas with lepidic-predominant patterns;

(2) moderately differentiated, invasive adenocarcinomas with acinar-predominant patterns; and

(3) poorly differentiated, adenocarcinomas with solid-predominant patterns.

A well-preserved lung architecture (Figure 4, A through C), with slight alveolar septal thickening from collagen deposition, was seen in low-magnification images of a well-differentiated adenocarcinoma (with a lepidic-predominant pattern). In contrast, invasive adenocarcinomas with both acinar-predominant (Figure 4, D through F) and solid-predominant (Figure 4, G through I) patterns showed increases in collagen content.

Our proof-of-principle pilot study indicates the potential utility of MPM for differentiating nonneoplastic from neoplastic lung tissue in fresh, ex vivo specimens without the use of exogenous contrast agents. Furthermore, study pathologists successfully identified the histologic subtypes of tumor and recognized inflammatory cells, such as lymphocytes and smoker macrophages. We also performed collagen quantification in adenocarcinomas and demonstrated its correlation with the degree of differentiation.

Indeed, the diagnostic potential of MPM for differentiating malignant from benign/inflammatory lesions has been previously investigated in multiple organ systems in both animal models and human tissues.3,12–19 Specifically, normal and diseased lung have been investigated in both small animals and in ex vivo human tissue using MPM.20–26 However, most studies focused on extracellular matrix remodeling associated with lung pathologies.22,23,25,26 To date, few studies have explored the potential of MPM for differentiating benign lesions from neoplastic ones.

. Our study is the first, to our knowledge, to present not only a detailed histology of normal human lung tissue obtained with MPM but also to show the histologic features that can be used to identify a variety of inflammatory, preneoplastic, and neoplastic lesions, in accordance with World Health Organization10 and International Association for the Study of Lung Cancer9 criteria. Furthermore, we demonstrated the ability of a pulmonary pathologist and a general surgical pathologist to differentiate between lesion subtypes in a blinded fashion with high reliability

 

 

The Human Genome Project

j.craigventer

 

 

 

 

 

 

 

 

 

 

 

J. Craig Venter (Photo credit: Wikipedia)

The Human Genome Project, driven by Francis Collins at NIH, and by Craig Venterat the Institute for Genome Research (TIGR) had parallel projects to map the human chromosome, completed in 2003. It originally aimed to map the nucleotides contained in a human haploid reference genome (more than three billion). TIGR was the first complete genomic sequencing of a free living organism, Haemophilus influenzae, in 1995. This used a shotgun sequencing technique pioneered earlier, but which had never been used for a whole bacterium.
Venter broke away from the HGP and started Celera in 1998 because of resistance to the shotgun sequency method, and his team completed the genome sequence in three years – seven years’ less time than the HGP timetable (using the gene of Dr. Venter). TIGR eventually sequenced and analyzed more than 50 microbial genomes. Its bioinformatics group developed

  • pioneering software algorithms that were used to analyze these genomes,
  • including the automatic gene finder GLIMMER and
  • the sequence alignment program MUMmer.

In 2002, Venter created and personally funded the J. Craig Venter Institute (JCVI) Joint Technology Center (JTC), which specialized in high throughput sequencing.  The JTC, in the top ranks of scientific institutions worldwide, sequenced nearly 100 million base pairs of DNA per day for its affiliated institutions (JCVI) .

He received his his Ph.D. degree in physiology and pharmacology from the University of California, San Diego in 1975 under biochemist Nathan O. Kaplan. A full professor at the State University of New York at Buffalo, he joined the National Institutes of Health in 1984. There he learned of a technique for rapidly identifying all of the mRNAs present in a cell and began to use it to identify human brain genes. The short cDNA sequence fragments discovered by this method are calledexpressed sequence tags (ESTs), a name coined by Anthony Kerlavage at TIGR.
Venter believed that shotgun sequencing was the fastest and most effective way to get useful human genome data. There was a belief that shotgun sequencing was less accurate than the clone-by-clone method chosen by the HGP, but the technique became widely accepted by the scientific community and is still the de facto standard used today.

References

Shreeve, James (2004). The Genome War: How Craig Venter Tried to Capture the Code of Life and Save the World. Knopf. ISBN 0375406298.
Sulston, John (2002). The Common Thread: A Story of Science, Politics, Ethics and the Human Genome. Joseph Henry Press. ISBN 0309084091.
“The Human Genome Project Race”. Center for Biomolecular Science & Engineering,UC Santa Cruz. Retrieved 20 March 2012.
Venter, J. Craig (2007). A Life Decoded: My Genome: My Life. Viking Adult. ISBN 0670063584.

Use of a Fluorophor Probe

An article has been discussed by Dr.  Tilda Barilya on use of a sensitive fluorescent probe in the near IR spectrum at > 700 nm to identify malignant ovarian cells in-vivo in abdominal exploration

  • by tagging an overexpressed FR-α (folate-FITA)

The author makes the point that:

  • In ovarian cancer, the FR-α appears to constitute a good target because it is overexpressed in 90–95% of malignant tumors, especially serous carcinomas.
  • Targeting ligand, folate, is attractive as it is nontoxic, inexpensive and relatively easily conjugated to a fluorescent dye to create a tumor-specific fluorescent contrast agent.
  • The report is identified as “ the first in-human proof-of-principle of the use of intraoperative tumor-specific fluorescence imaging in staging and debulking surgery for ovarian cancer using the systemically administered targeted fluorescent agent folate-FITC.”

While this does invoke possibilities for prognosis, the decision to perform the surgery,

  • whether laparoscopic or open, is late in the discovery process. However,

it does suggest the possibility that the discovery and the treatment might be combined

  • if the biomarker itself had the fluorescence to identify the overexpression, but
  • it also is combined with a tag to block the overexpession. This hypothetical possibility is now expressed below.

http://pharmaceuticalintelligence.com/2013/01/19/ovarian-cancer-and-fluorescence-guided-surgery-a-report/

Gene Editing

Aviva Lev-Ari, PhD, RD

Aviva Lev-Ari, PhD, RD

 

 

 

 

 

 

Dr. Aviva Lev-Ari reports that a new technique developed at MIT Broad Institute and the Rockefeller University can edit DNA in precise locations

taken from Science News titled Editing Genome With High Precision: New Method to Insert Multiple Genes in Specific Locations, Delete Defective Genes”.

Using this system, scientists can alter

  • several genome sites simultaneously and
  • can achieve much greater control over where new genes are inserted

According to Feng Zhang, this is an improvement beyond splicing the gene in specific locations and

insertion of complexes difficult to assemble known as

transcription activator-like effector nucleases (TALENs).

  • The researchers create DNA-editing complexes
  • using naturally occurring bacterial protein-RNA systems
  • that recognize and snip viral DNA, including
  • a nuclease called Cas9 bound to short RNA sequences.
  • they target specific locations in the genome, and
  • when they encounter a match, Cas9 cuts the DNA.

This approach can be used either to

  • disrupt the function of a gene or
  • to replace it with a new one.
  • To replace the gene, a DNA template for the new gene has to be copied into the genome after the DNA is cut. The method is also very precise –
  • if there is a single base-pair difference between the RNA targeting sequence and the genome sequence, Cas9 is not activated.

In its first iteration, it appears comparable in efficiency to what

zinc finger nucleases and TALENs have to offer.

The research team has deposited the necessary genetic components with a nonprofit called Addgene, and they have also created a website with tips and tools for using this new technique.

The above story is reprinted from materials provided by Massachusetts Institute of Technology.

The original article was written by Anne Trafton. Le Cong, F. Ann Ran, David Cox, Shuailiang Lin, Robert Barretto, Naomi Habib, Patrick D. Hsu, Xuebing Wu, Wenyan Jiang, Luciano Marraffini, and Feng Zhang.

Multiplex Genome Engineering Using CRISPR/Cas Systems.
Science, 3 January 2013   DOI: 10.1126/science.1231143.
http://Science.comEditing genome with high precision: New method to insert multiple genes in specific locations, delete defective genes. ScienceDaily. Retrieved January 20, 2013, from http://www.sciencedaily.com­ /releases/2013/01/130103143205.htm?  goback=%2Egde_4346921_member_205356312.

Dr. Lev-Ari also reports on a study of early detection of breast cancer in “Mechanism involved in Breast Cancer Cell Growth: Function in Early Detection & Treatment“, by Dr. Rotem Karni and PhD student Vered Ben Hur at the Institute for Medical Research Israel-Canada of the Hebrew University.
http://pharmaceuticalintelligence.com/2013/01/17/mechanism-involved-in-breast-cancer-cell-growth-function-in-early-detection-treatment/
These researchers have discovered a new mechanism by which breast cancer cells switch on their aggressive cancerous behavior. The discovery provides a valuable marker for the early diagnosis and follow-up treatment of malignant growths.
The method they use is

  • RNA splicing and insertion.
  • The information needed for the production of a mature protein is encoded in segments called exons .
  • In the splicing process, the non-coding segments of the RNA (introns) are spliced from the pre-mRNA and
  • the exons are joined together.

Alternative splicing is when a specific ”scene” (or exon) is either inserted or deleted from the movie (mRNA), thus changing its meaning.

  • Over 90 percent of the genes in our genome undergo alternative splicing of one or more of their exons, and
  • the resulting changes in the proteins encoded by these different mRNAs are required for normal function.
  • the normal process of alternative splicing is altered in cancer, and
  • ”bad” protein forms are generated that aid cancer cell proliferation and survival.

The researchers reported in online Cell Reports that breast cancer cells

  • change the alternative splicing of an important enzyme, calledS6K1, which is
  • a protein involved in the transmission of information into the cell.
  • when this happens, breast cancer cells start to produce shorter versions of this enzyme and
  • these shorter versions transmit signals ordering the cells to grow, proliferate, survive and invade other tissues (otherwise proliferation is suppressed)

The application to biotherapeutics would be to ”reverse” the alternative splicing of S6K1 in cancer cells back to the normal situation as a novel anti-cancer therapy.

 

Imaging Mass Cytometry

This literature review shows how researchers used CyTOF mass cytometry to obtain spatial resolution of cell samples.

The authors used mass cytometry to measure heterogeneity in breast cancer tumors using FFPE breast cancer samples. [© Kheng Guan Toh – Fotolia.com]

The integration of mass spectrometry (specifically laser ablation of the sample in combination with inductively coupled plasma mass spectrometry) with flow cytometry instrumentation along with sensitive and rare earth metal labels

  • has enabled multiplexing of up to 32 cell markers (see Assay Drug Dev Technol 2011;9:567 commentary “Flow cytometry goes atomic;” CyTOF system sold by Fluidigm, formerly DVS Sciences).

This process employs typical immunocytochemistry techniques, but the antibodies are tagged with rare earth metal isotopes (predominately lanthanides)

  • that act as specific reporters of cellular proteins.

Comparison of these rare earth–labeled antibodies to typical fluorescent antibody labels supports that

  • these labels do not affect the specificity or sensitivity of the antibodies. In this article the authors* extend this method to obtain spatial resolution of cell samples.

 

mass cytometry to measure heterogeneity in breast cancer tumors using FFPE

mass cytometry to measure heterogeneity in breast cancer tumors using FFPE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Workflow of imaging mass cytometry.

 

 

is correlated with the position of the laser spot as it is scanned across the sample with 1 μm resolution.In the method, the signals from the rare earth reporters following laser ablation of the sample

The limit of detection is determined to be ∼500 molecules. The data can then be plotted based on the position of each ion spot for each rare earth reporter, and these images

  • are then overlaid to create a high-dimensional image that can be analyzed (Figure).

Measurement of a 0.5 mm × 0.5 mm area at 1 μm resolution takes ∼5 h. The system is capable of measuring 100 analytes simultaneously, but only 32 rare earth metal chelates are currently available. The authors applied this method

  • to measure heterogeneity in breast cancer tumors using formalin-fixed, paraffin-embedded (FFPE) breast cancer samples.

A total of 21 FFPE samples were analyzed using 32-plex imaging mass cytometry covering cell markers and phosphoproteins. Differences in expression even within the same tumor sample were noted, and

  • the subpopulations branch points often contained markers used for patient classification. Some exceptions occurred; for example,
  • Her2 was detected and confirmed in one triple-negative case.

This high-dimensional imaging should increase our understanding of tumor biology and pathologies.

*Abstract from Nature Methods 2014, Vol. 11: 403–406

Mass cytometry enables high-dimensional, single-cell analysis of cell type and state. In mass cytometry, rare earth metals are used as reporters on antibodies. Analysis of metal abundances using the mass cytometer

  • allows determination of marker expression in individual cells. Mass cytometry has previously been applied only to cell suspensions.

To gain spatial information, we have coupled

  • immunohistochemical and immunocytochemical methods
  • with high-resolution laser ablation to CyTOF mass cytometry.

This approach enables the simultaneous imaging of 32 proteins and protein modifications at subcellular resolution;

  • with the availability of additional isotopes, measurement of over 100 markers will be possible.

We applied imaging mass cytometry to human breast cancer samples, allowing delineation of cell subpopulations and cell–cell interactions and highlighting tumor heterogeneity. Imaging mass cytometry

  • complements existing imaging approaches.

It will enable basic studies of tissue heterogeneity and function and

  • support the transition of medicine toward individualized molecularly targeted diagnosis and therapies.

 

Preventing a cellular identity crisis 

http://news.sciencemag.org/sites/default/files/styles/thumb_article_l/public/sn-criticalgenesH.jpg?itok=0wmD-o4a

 

Staying true.

 

neural progenitor cells keep their identities

neural progenitor cells keep their identities

 

 

 

 

 

Researchers have discovered a molecular signature in the genome that might help cells like these neural progenitor cells keep their identities throughout their lives.

By Mitch Leslie 31 July 2014

Cells rely on different ways to establish who they are and what they do.  A novel mechanism

  • marks the identities of different kinds of cells in the human body—
  • and prevents them from transforming into another type altogether.

Scientists learned decades ago to read the basic genetic code by which cells convert a string of DNA bases into a protein’s amino acids. But for more than 10 years,

  • they’ve been trying to crack what’s known as the histone code, a more complex cipher embedded within organisms’ genomes.

Histones are the proteins that DNA coils around in chromosomes. Chemically tweaking histones in a variety of ways can

  • adjust the activity of genes, turning them up or down. For example,
  • cells shut off genes by attaching three methyl groups to a specific spot on a histone type known as H3.
  • affixing three methyl groups to another H3 location, a modification known as H3K4me3, has a different effect.

Cells typically add the H3K4me3 tags to histones in small sections of the genome, but researchers noticed that

  • sometimes the tag can sprawl across much larger areas,
  • modifying broad swaths of histones.

To find out whether these large blocks of histones carrying H3K4me3 tags convey a message in the histone code, molecular geneticist Anne Brunet of Stanford University in Palo Alto, California, and colleagues

  • traced their occurrence in more than 20 different cell types.

They found that the longest stretches pinpoint different sets of genes in different types of cells. As a result, the researchers realized

  • they could discriminate liver cells from, say, muscle cells or kidney cells
  • based only on the chromosomal locations of the largest H3K4me3 blocks. In addition,
  • they noticed that these stretches tended to mark genes that are crucial for a cell type’s function or
  • that help make it distinct. In embryonic stem cells, for instance,
  • they occur on genes that control the cells’ capacity to specialize.

The researchers further demonstrated that the labels mark cell identity genes by

  • using a technique called RNA interference (RNAi) in adult neural progenitor cells,
  • which can morph into any cell type in the brain.

As the researchers revealed online today in Cell,

  • they applied RNAi to dial down the genes that carried large blocks of H3K4me3 tags and
  • found that it impaired the cells’ ability to reproduce and to spawn neurons. However,
  • the progenitor cells could still divide normally if the researchers quieted genes that had only short sections of H3K4me3 tags or none at all.

The presence of long stretches of H3K4me3 markers

  • might help cells keep their identities for life.
  • “we’ve discovered a new signature,” Brunet says.

Although many other scientists have studied H3K4me3 tags, “the concept that this one mark

  • can distinguish all these cell types
  • the discovery could allow quick identification of cell types,
  • which would be useful in situations such as cancer diagnosis.

Posted in Biology

 

Gene Deletion Slows Aging and Reduces Cancer Risk

gene deletion

gene deletion

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Source: © Gernot Krautberger – Fotolia.com

Scientists at the Wistar Institute say they have discovered that

  • mice lacking a specific protein live longer lives with fewer age-related illnesses.

The mice that lack the TRAP-1 protein, demonstrated less age-related tissue degeneration, obesity, and spontaneous tumor formation when compared to normal mice. Their findings could change how scientists view the metabolic networks within cells. In healthy cells,

TRAP-1 is an important regulator of metabolism and

  •  regulates energy production in mitochondria, organelles that generate chemically useful energy for the cell.

In the mitochondria of cancer cells, TRAP-1 is universally overproduced.

The Wistar team’s report (“Deletion of the Mitochondrial Chaperone TRAP-1 Uncovers Global Reprogramming of Metabolic Networks”), which appears in Cell Reports, shows how ”

  • knockout” mice bred to lack the TRAP-1 protein compensate for this loss by switching to alternative cellular mechanisms for making energy.

“We see this astounding change in TRAP-1 knockout mice, where they show fewer signs of aging and are less likely to develop cancers,” said Dario C. Altieri. M.D.,  director of the Wistar Institute’s National Cancer Institute-designated Cancer Center. “Our findings provide

  • an unexpected explanation for how TRAP-1 and related proteins regulate metabolism within our cells.
  • we didn’t expect to see  healthier mice with fewer tumors.

Dr. Altieri and his colleagues created the TRAP-1 knockout mice as part of their

  • ongoing investigation into the drug Gamitrinib, which targets the protein in the mitochondria of tumor cells.

TRAP-1 is a member of the heat shock 90 (HSP90) protein family, which are

  • chaperone proteins that guide the physical formation of other proteins and
  • serve a regulatory function within mitochondria.
  • Tumors use HSP90 proteins like TRAP-1 to help survive therapeutic attack.

In tumors,

  • the loss of TRAP-1 is devastating, triggering a host of catastrophic defects, including
  • metabolic problems that ultimately result in in death of the tumor cells,, BUT
  • Mice that lack TRAP-1 from the start have three weeks in the womb to compensate for the loss of the protein.”

In the knockout mice, the loss of TRAP-1

  1. causes mitochondrial proteins to misfold, which then
  2. triggers a compensatory response that causes cells to consume more oxygen and metabolize more sugar. which
  3. causes mitochondria in knockout mice to produce deregulated levels of ATP,
  4. the chemical used as an energy source to power all the everyday molecular reactions that allow a cell to function.

This increased mitochondrial activity actually creates a moderate boost in oxidative stress (free radical damage) and the associated DNA damage. While DNA damage may seem counterproductive to longevity and good health,

  • the low level of DNA damage actually reduces cell proliferation—slowing growth down to allow the cell’s natural repair mechanisms to take effect.

“TRAP-1−/− mice are viable and showed reduced incidence of age-associated pathologies including – obesity, inflammatory tissue degeneration, dysplasia, and spontaneous tumor formation,- accompanied by

  • global upregulation of oxidative phosphorylation and glycolysis transcriptomes, causing

 

 

  1. deregulated mitochondrial respiration,
  2. oxidative stress,
  3. impaired cell proliferation, and
  4. a switch to glycolytic metabolism in vivo.

These data identify TRAP-1 as

  1. a central regulator of mitochondrial bioenergetics, and
  2. this pathway could contribute to metabolic rewiring in tumors.”

“Our findings strengthen the case

  • for targeting HSP90 in tumor cells, but it
  • may have implications for metabolism and longevity,” explained Dr. Altieri.

GEN News 8-1-2014

 

The role of the Wnt signaling pathway in cancer stem cells: prospects for drug development

Yong-Mi Kim, Michael Kahn
1Children’s Hospital Los Angeles, Division of Hematology and Oncology, Department of Pediatrics and Pathology, 2Department of Biochemistry and Molecular Biology, Keck School of Medicine of University of Southern California, 3Norris Comprehensive Cancer Research Center, University of Southern California, Los Angeles, CA, USA

Research and Reports in Biochemistry July 2014; 4:1—12
http://dx.doi.org/10.2147/RRBC.S53823

Abstract: Cancer stem cells (CSCs), also known as tumor initiating cells are now considered to be

  • the root cause of most if not all cancers, evading treatment and giving rise to disease relapse.

They have become a central focus in new drug development.

  1. Prospective identification,
  2. understanding the key pathways that maintain CSCs, and
  3. being able to target CSCs, particularly
  • if the normal stem cell population could be spared, could offer an incredible therapeutic advantage.

The Wnt signaling cascade is critically important in stem cell biology, both

  • in homeostatic maintenance of tissues and organs through their respective somatic stem cells and
  • in the CSC/tumor initiating cell population.

Aberrant Wnt signaling is associated with a wide array of tumor types. Therefore, the ability to

  • safely target the Wnt signaling pathway offers enormous promise to target CSCs. However,
  • just like the sword of Damocles, significant risks and concerns regarding targeting such a critical pathway in normal stem cell maintenance and tissue homeostasis remain ever present.

With this in mind, we review recent efforts in modulating the Wnt signaling cascade and critically analyze therapeutic approaches at various stages of development.

Keywords: beta-catenin, CBP, p300, wnt inhibition

 

 

A*STAR Scientists Pinpoint Genetic Changes that Spell Cancer: Fruit flies light the way for scientists to uncover genetic changes.

With a new approach, researchers may rapidly distinguish the range of

  • genetic changes that are causally linked to cancer (i.e.“driver” mutations)
  • versus those with limited impact on cancer progression.

This study published in the prestigious journal Genes & Development could pave the way

  • to design more targeted treatment against different cancer types, based on
  • the specific cancer-linked mutations present in the patient,
  • an advance in the development of personalized medicine.

Signaling pathways involved in tumour formation are conserved from fruit flies to humans. In fact, about 75 percent of known human disease genes have a recognizable match in the genome of fruit flies.
Leveraging on their genetic similarities, Dr Hector Herranz, a post-doctorate from the Dr. Stephen Cohen’s team developed an innovative strategy to genetically screen the whole fly genome for “cooperating” cancer genes.

  • These genes appear to have little or no impact on cancer.
  • However, they cooperate with other cancer genes, so that
  • the combination causes aggressive cancer, which
  • neither would cause alone.

In this study, the team was specifically looking for genes that

  • could cooperate withEGFR “driver” mutation,
  • a genetic change commonly associated with breast and lung cancers in humans.
  • SOCS5 (reported in this paper) is one of the several new “cooperating” cancer genes to be identified.

Already, there are indications that levels of SOCS5 expression are

  • reduced in breast cancer, and
  • patients with low levels of SOCS5 have poor prognosis.”

The IMCB team is preparing to explore the use of SOCS5 as a biomarker in diagnosis for cancer.

 

Probing What Fuels Cancer

http://genes&development.com

‘Altered cellular metabolism is a hallmark of cancer,’ says Dr Patrick Pollard, in the Nuffield Department of Clinical Medicine at Oxford.

Most cancer cells get the energy they need predominantly through

  • a high rate of glycolysis – allowing cancer cells deal with the low oxygen levels that tend to be present in a tumour. But
  • whether dysfunctional metabolism causes cancer, as Warburg believed, or is something that happens afterwards is a different question.
  • In the meantime, gene studies rapidly progressed and indicated that genetic changes occur in cancer.

DNA mutations spring up all the time in the body’s cells, but

  • most are quickly repaired.
  • Alternatively the cell might shut down or be killed off (apoptosis) before any damage is caused. However, the repair machinery is not perfect.
  • If changes occur that bypass parts of the repair machinery or sabotage it,
  • the cell can escape the body’s normal controls on growth and
  • DNA changes can begin to accumulate as the cell becomes cancerous.

Patrick believes certain changes in cells can’t always be accounted for by ‘genetics.’
He is now collaborating with Professor Tomoyoshi Soga’s large lab at Keio University in Japan, which has been at the forefront of developing the technology for metabolomics research over the past couple of decades.

The Japanese lab’s ability to

  • screen samples for thousands of compounds and metabolites at once, and
  • the access to tumour material and cell and animal models of disease
  • enables them to probe the metabolic changes that occur in cancer.

There is reason to believe that

  • dysfunctional cell metabolism is important in cancer.
  • genes with metabolic functions are associated with some cancers
  • changes in the function of a metabolic enzyme have been implicated in the development of gliomas.

These results have led to the idea that

  • some metabolic compounds, or metabolites, when they accumulate in cells, can cause changes to metabolic processes and set cells off on a path towards cancer.

Patrick Pollard and colleagues have now published a perspective article in the journal Frontiers in Molecular and Cellular Oncology that proposes

  • fumarate as such an ‘oncometabolite’. Fumarate is a standard compound involved in cellular metabolism.

The researchers summarize evidence that shows how

  • accumulation of fumarate when an enzyme goes wrong affects various biological pathways in the cell.
  • It shifts the balance of metabolic processes and disrupts the cell in ways that could favour development of cancer.

Patrick and colleagues write in their latest article that the shift in focus of cancer research to include cancer cell metabolism ‘has highlighted how woefully ignorant we are about the complexities and interrelationships of cellular metabolic pathways’.

 

NATURE GENETICS | BRIEF COMMUNICATION

 

Recurrent SMARCA4 mutations in small cell carcinoma of the ovary

Nature Genetics (2014); 46: 424–426    http://dx.doi.org:/10.1038/ng.2922

 

Small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) is a rare, highly aggressive form of ovarian cancer primarily diagnosed in young women. We identified

  • inactivating biallelic SMARCA4 mutations in 100% of the 12 SCCOHT tumors examined.

Protein studies confirmed loss of SMARCA4 expression, suggesting a key role for the SWI/SNF chromatin-remodeling complex in SCCOHT.

At a glance

Figures

Figure 1: SMARCA4 mutations in SCCOHT and TCGA samples.close

SMARCA4 mutations in SCCOHT and TCGA samples.close

SMARCA4 mutations in SCCOHT and TCGA samples.close

 

 

 

 

 

 

 

 

 

 

 

 

(a) Domain structure of the SMARCA4 protein (UniProt, SMCA4_HUMAN) overlaid with the alterations identified in 11 of the 12 SCCOHT cases in this study (case numbers in parentheses; case 103 with exon deletion is not shown). SNF2_N, SNF…

http://www.nature.com/ng/journal/v46/n5/carousel/ng.2922-F1.jpg

Figure 2: Analyses of the splice-site mutation in case 102.close

Analyses of the splice-site mutation in case 102.close

Analyses of the splice-site mutation in case 102.close

 

 

 

 

 

 

 

 

 

 

(a) Immunoblotting with antibody to the N terminus of SMARCA4. A high-grade serous ovarian cancer cell line (PEO4) and frozen tumor samples from two individuals with high-grade serous ovarian cancer (HGOC) were used as positive control…

http://www.nature.com/ng/journal/v46/n5/carousel/ng.2922-F2.jpg

 

References

 

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Download references

Primary authors

 

These authors contributed equally to this work.

Petar Jelinic & Jennifer J Mueller, Department of Surgery

Petar Jelinic, Jennifer J Mueller, Narciso Olvera, Fanny Dao & Douglas A Levine
Department of Surgery

Sasinya N Scott, Ronak Shah, Robert A Soslow & Michael F Berger
Department of Pathology,

JianJiong Gao & Nikolaus Schultz
Computational Biology Program,

Mithat Gonen  Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, New York, USA.

Corresponding author

Douglas A Levine

Supplementary information

 

Supplementary Figures

  1. Supplementary Figure 1: Sequence analyses forSMARCA4 in SCCOHT cases. (715 KB)

Next-generation sequence coverage demonstrating identified variants (top panels) and validation through Sanger sequencing (bottom panels).

  1. Supplementary Figure 2:SMARCA4 gene expression across TCGA tumors for cases with available mutation and RNA-seq data (RSEM). (366 KB)

A correlation is seen between inactivating SMARCA4 mutations and decreased gene expression across various solid tumors. A two-sided Student’s t test was used to compare samples with non-missense mutations and other samples without mutations or with only missense mutations. For all TCGA samples, the mean RNA-seq RSEM (2,050, s.d. of 1,760) was less in samples with non-missense mutations than in other samples without mutations or with only missense mutations (3,724, s.d. of 1,692; P = 8.7 × 10−4). For TCGA lung adenocarcinoma samples, the mean RNA-seq RSEM (601, s.d. of 370) was less in samples with non-missense mutations than in other samples without mutations or with only missense mutations (3,330, s.d. of 1,524; P = 2 × 10−8).

  1. Supplementary Figure 3: Immunohistochemistry for SMARCA4 in SCCOHT cases. (566 KB)

High-grade serous ovarian carcinoma is used as a positive control. Case numbers are indicated in each panel. Immunohistochemistry results are provided in Supplementary Table 1. Note the intense staining of blood vessels and stromal cell nuclei as internal controls.

  1. Supplementary Figure 4: Analysis of homozygous deletion in case 103. (109 KB)

Next-generation sequence coverage demonstrating that exons 25 and 26 are deleted. An electropherogram from Sanger sequencing of cDNA validating that the deletion retains an ORF from exon 24 to exon 27 (Panel A). One-step RT-PCR confirms that tumor tissue yields a single band with primers that span exons 24 and 27 (Panel B; *, nonspecific band). One-step RT-PCR with primers targeting regions upstream and downstream from the deletion site show equal expression, demonstrating continuation of transcription downstream from the deletion (Panel C).

  1. Supplementary Figure 5: Analysis of splice-site variant in case 102. (90 KB)

One-step RT-PCR confirms that the exon-intron band is preferentially expressed over the exon-exon band in tumor tissue (Panel A). One-step RT-PCR with primers targeting regions upstream and downstream from the mutation site show equal expression, demonstrating continuation of transcription downstream from the mutation (Panel B). Immunoblots are shown in Figure 2b. The exon-exon primers detected weaker bands, reflecting loss of expression in tumor tissues compared with normal tissues in cases with splice-site mutations. The exon-intron primers demonstrated equivalent to greater expression of the retained intron in the tumor tissues. As SMARCA4 introns may be retained in non-cancer tissues, some intronic expression is expected in normal tissues. These data taken together indicate preferential intronic expression, as expected, in cDNA sequenced from tumor samples with splice-site mutations.

  1. Supplementary Figure 6: Sequence analyses forSMARCA4 in the H1299 cell line. (134 KB)

An electropherogram from Sanger sequencing of genomic DNA validating a 69-nt deletion in the ORF of this control cell line that results in loss of protein expression, as shown inFigure 2b.

  1. Supplementary Figure 7: SMARCA4 effect on cell proliferation. (131 KB)

SMARCA4 overexpression in H1299 cells. Representative immunoblot from three biologic replicates demonstrates a correlation between increased SMARCA4 and p21 expression (Panel A). Cell growth assessment in H1299 cells overexpressing SMARCA4. Mean cell counts from three biologic replicates (Panel B). Representative immunoblot confirmed SMARCA4 knockdown in 293T cells using shRNA. As a control, shNTC (Non-Targeting Control) was used (Panel C). XTT proliferation assay in 293T cells depleted of SMARCA4. Means represent three independent experiments (Panel D).

  1. Supplementary Figure 8: Overall survival among lung adenocarcinoma TCGA cases based on inactivatingSMARCA4  (174 KB)

Median overall survival was 11.6 months among 6 patients with inactivating SMARCA4mutations compared with 44.6 months for 197 patients without inactivating mutations.

  1. Supplementary Figure 9: Histopathological features of an SCCOHT. (979 KB)

The typical histopathological features of SCCOHT, including a combination of small neoplastic cells forming a pseudofollicular space and larger rhabdoid cells, are visible in a sample obtained from 1 of 12 tumors that were subjected to target capture and massively parallel DNA sequencing (hematoxylin and eosin).

PDF files

  1. Supplementary Text and Figures (5,357 KB)

Supplementary Figures 1–9 and Supplementary Tables 1–5

 

 

CRISPR-Cas9 Foundational Technology originated at UC, Berkeley & UCSF, Broad Institute is developing Biotech Applications — Intellectual Property emerging as Legal Potential Dispute

Curator and Reporter: Aviva Lev-Ari, PhD, RN

http://pharmaceuticalintelligence.com/2014/06/18/crispr-cas9-foundational-technology-originated-at-uc-berkeley-ucsf-broad-institute-is-developing-biotech-applications-intellectual-property-emerging-as-legal-potential-dispute/

 

CRISPR-Cas9 Foundational Technology – The definition of “Prior Art” is at a very high stack, June 2014.

On 6/16/2014 Dr. Aviva Lev-Ari published the following two articles:

Lecture Contents delivered at Koch Institute for Integrative Cancer Research, Summer Symposium 2014: RNA Biology, Cancer and Therapeutic Implications, June 13, 2014 @MIT
http://pharmaceuticalintelligence.com/2014/06/16/lecture-contents-delivered-at-koch-institute-for-integrative-cancer-research-summer-symposium-2014-rna-biology-cancer-and-therapeutic-implications-june-13-2014-mit/
Prediction of the Winner RNA Technology, the FRONTIER of SCIENCE on RNA Biology, Cancer and Therapeutics & The Start Up Landscape in Boston
http://pharmaceuticalintelligence.com/2014/06/16/prediction-of-the-winner-rna-technology-the-frontier-of-science-on-rna-biology-cancer-and-therapeutics-the-start-up-landscape-in-boston/

 

Other related articles on CRISPR-Cas9 Technology published on this Open Access Online Scientific Journal include the following:

2:15 – 2:45, 6/13/2014, Jennifer Doudna “The biology of CRISPRs: from genome defense to genetic engineering”

http://pharmaceuticalintelligence.com/2014/06/13/215-245-6132014-jennifer-doudna-the-biology-of-crisprs-from-genome-defense-to-genetic-engineering/

 

Ribozymes and RNA Machines – Work of Jennifer A. Doudna

http://pharmaceuticalintelligence.com/2013/04/15/ribozymes-and-rna-machines-work-of-jennifer-a-doudna/

 

CRISPR @MIT – Genome Surgery

http://pharmaceuticalintelligence.com/2014/04/21/crispr-mit-genome-surgery/


Gene Therapy and the Genetic Study of Disease: @Berkeley and @UCSF – New DNA-editing technology spawns bold UC initiative as Crispr Goes Global

http://pharmaceuticalintelligence.com/2014/03/27/gene-therapy-and-the-genetic-study-of-disease-berkeley-and-ucsf-new-dna-editing-technology-spawns-bold-uc-initiative-as-crispr-goes-global/

Diagnosing Diseases & Gene Therapy: Precision Genome Editing and Cost-effective microRNA Profiling

http://pharmaceuticalintelligence.com/2013/03/28/diagnosing-diseases-gene-therapy-precision-genome-editing-and-cost-effective-microrna-profiling/

An expanded-DNA Biology from Scripps Research Institute: Beyond A-T and C-G: Applications for new Medicines and Nanotechnology

http://pharmaceuticalintelligence.com/2014/05/11/an-expanded-dna-biology-from-scripps-research-institute-beyond-a-t-and-c-g-applications-for-new-medicines-and-nanotechnology/

 

Evaluate your Cas9 Gene Editing Vectors: CRISPR/Cas Mediated Genome Engineering – Is your CRISPR gRNA optimized for your cell lines?

http://pharmaceuticalintelligence.com/2014/03/25/evaluate-your-cas9-gene-editing-vectors-crisprcas-mediated-genome-engineering-is-your-crispr-grna-optimized-for-your-cell-lines/

 

2:15 – 2:45, 6/13/2014,  Jennifer Doudna  “The biology of CRISPRs: from genome defense to genetic engineering” 

http://pharmaceuticalintelligence.com/2014/06/13/215-245-6132014-jennifer-doudna-the-biology-of-crisprs-from-genome-defense-to-genetic-engineering/

About CRISPR “this technology will revolutionize biology in the same way PCR did,” Rudolf Jaenisch introducing Jennifer Doudna

Top CRISPR Related Publications

http://blog.appliedstemcell.com/top-crispr-related-publications/

Capturing key concepts of Prof.  Jennifer Doudna’s Lecture @ KI Symposium:

  • acquired immunity in bacteria
  • three steps:
  1. adaptation
  2. biogenesis
  3. interference

 

 

Big Pharma is using its venture cash to outsource early R&D to biotech

July 31, 2014 | By John Carroll

Analysts at Silicon Valley Bank have been crunching the numbers on biotech investing, and they have found that

  • a group of busy corporate venture arms has fundamentally changed the landscape for startups and
  • the entire field of early-stage drug development–
  • with some big implications for the current crop of industry upstarts.

Over the past two years corporate venture funding for biotech companies has surged back to 2008 levels, the bank’s analysts conclude, and

  • it now adds up to a much larger portion of the total amount of investment cash that’s available to biotechs.

Last year these corporate financing arms accounted for slightly

  • more than a third of all the cash that flowed into biotech, according to SVB. And
  • the corporate VCs have a big appetite for investing in early-stage rounds.
Courtesy of Silicon Valley Bank

Courtesy of Silicon Valley Bank

 

 

 

 

 

 

 

 

 

 

 

 

Courtesy of Silicon Valley Bank

“I think we’ve reached a healthy level of funding in the sector right now,” says Jon Norris, the author of the report and managing director at Silicon Valley Bank. He adds that

  • with the IPO window still open to biotechs, a lot of early- or mid-stage companies are now choosing to jump through
  • to the public market rather than make a deal with pharma.

The IPO alternative has also made it possible to drive up the value of biotech assets, which now command record payments.

But that’s a trend that can’t run forever.

“This can’t run out too much longer into 2015,” says Norris. “I can see it starting to close.”

As the window shuts, he adds, you can expect to see the number of M&A deals rise. And the biggest biotech deals will likely be worth more, as big exits–defined as deals with an upfront of $75 million or more–jumped to an average record high of $549 million last year, a 10% spike over 2012.

Courtesy of Silicon Valley Bank 2

Courtesy of Silicon Valley Bank 2

 

 

 

 

 

 

 

 

 

 

 

 

 

Courtesy of Silicon Valley Bank

In its analysis, Silicon Valley Bank concludes that the early-stage investment gamble now

  • amounts to a strategic move by the top Big Pharma companies to outsource a considerable portion of their early-stage R&D work,
  • priming the cash pump directly through their own venture arms as well as by investing in many of the new venture funds filling up with risk capital. And
  • the change-up is likely to continue to drive partnering as well as Big Pharma
  • forges a new round of development pacts and M&A deals with their venture colleagues involved in biotech.

“We’ve all seen over the last few years the pullback in overall R&D spending by pharma and biotech,” says Norris. “There’s a tendency for these (pharma) folks to outsource their innovation.”

Not surprisingly, experimental

  • cancer drugs are attracting the bulk of Big Pharma’s attention and corporate cash, followed by
  • platform technologies that generate new leads, metabolics, ophthalmology, cardiovascular, CNS, dermatology, GI and inflammation, says SVB.

The leading corporate venture investors in the industry include Novartis ($NVS),Astellas, Pfizer ($PFE), S.R. One ($GSK), Amgen ($AMGN) and J&J Development Corp. ($JNJ). And nearly 90% of top corporate investment deals are directed at Series A or B rounds. More than half of these new investments, says SVB, were in preclinical or Phase I companies.

 

 

Extensive Promoter-Centered Chromatin Interactions Provide a Topological Basis for Transcription Regulation
(Li G, Ruan X, Auerbach RK, Sandhu KS, et al.) Cell 2012; 148(1-2): 84-98. http://cell.com

http://FrontiersMolecularCellularOncology.com

 

Using genome-wide Chromatin Interaction Analysis with Paired-End-Tag sequencing (ChIA-PET),
mapped long-range chromatin interactions associated with RNA polymerase II in human cells
uncovered widespread promoter-centered intragenic, extragenic, and intergenic interactions.

  • These interactions further aggregated into higher-order clusters
  • proximal and distal genes were engaged through promoter-promoter interactions.
  • most genes with promoter-promoter interactions were active and transcribed cooperatively
  • some interacting promoters could influence each other implying combinatorial complexity of transcriptional controls.

Comparative analyses of different cell lines showed that

  • cell-specific chromatin interactions could provide structural frameworks for cell-specific transcription,
  • and suggested significant enrichment of enhancer-promoter interactions for cell-specific functions.
  • genetically-identified disease-associated noncoding elements were spatially engaged with corresponding genes through long-range interactions.

Overall, our study provides insights into transcription regulation by

  • three-dimensional chromatin interactions for both housekeeping and
  • cell-specific genes in human cells.

 

New Nucleoporin: Regulator of Transcriptional Repression and Beyond.

NJ Sarma and K Willis
Nucleus 2012; 3(6): 1–8;     http://Nucleus.com © 2012 Landes Bioscience

 

Transcriptional regulation is a complex process that requires the integrated action of many multi-protein complexes.
The way in which a living cell coordinates the action of these complexes in time and space is still poorly understood.

  • nuclear pores, well known for their role in 3′ processing and export of transcripts, also participate in the control of transcriptional initiation.
  • nuclear pores interface with the well-described machinery that regulates initiation.

This work led to the discovery that

  • specific nucleoporins are required for binding of the repressor protein Mig1 to its site in target promoters.
  • Nuclear pores are involved in repressing, as well as activating, transcription.

Here we discuss in detail the main models explaining our result and consider what each implies about the roles that nuclear pores play in the regulation of gene expression.

 

Computational Design of Targeted Inhibitors of Polo-Like Kinase 1 ( lk1).

(KS Jani and DS Dalafave) Bioinformatics and Biology Insights 2012:6 23–31.
http://dx.doi.org:/10.4137/BBI.S8971

Computational design of small molecule putative inhibitors of Polo-like kinase 1 (Plk1) is presented. Plk1, which regulates the cell cycle, is often over expressed in cancers.

  • Down regulation of Plk1 has been shown to inhibit tumor progression.
  • Most kinase inhibitors interact with the ATP binding site on Plk1, which is highly conserved.
  • This makes the development of Plk1-specific inhibitors challenging, since different kinases have similar ATP sites.

However, Plk1 also contains a unique region called the polo-box domain (PBD), which is absent from other kinases.

  • the PBD site was used as a target for designed Plk1 putative inhibitors.
  • Common structural features of several experimentally known Plk1 ligands were first identified.
  • The findings were used to design small molecules that specifically bonded Plk1.
  • Drug likeness and possible toxicities of the molecules were investigated.
  • Molecules with no implied toxicities and optimal drug likeness values were used for docking studies.
  • Several molecules were identified that made stable complexes only with Plk1 and LYN kinases, but not with other kinases.
  • One molecule was found to bind exclusively the PBD site of Plk1.

Possible utilization of the designed molecules in drugs against cancers with over expressed Plk1 is discussed.

Conclusions

The previous discussions reviewed the status of an evolving personalized medicine multicentered and worldwide enterprise.  It is also clear from these reports that the search for targeted drugs matched to a cancer profile or signature has identified several approaches that show great promise.

  • We know considerably  more about metabolic pathways and linked changes in transcription that occur in neoplastic development.
  • There are several methods used to do highly accurate  insertions in gene sequences that are linked to specific metabolic changes, and
  • some may have significant implications for therapeutics, if
    • the link is a change that is associated with a driver mutation
    • the link can be identified by a fluorescent or other probe
    • the link is tied to a mRNA or peptide product that is a biomarker measured in the circulation
  • We have probes to genetic links to the control of many and interacting signaling pathways.
  • We know more about transcription through mRNA.
  • We are closer to the possibility that metabolic substrates, like ‘fumarate’ (a key intermediate in the TCA cycle), may provide a means to reverse regulate the neoplastic cells.
  • We may also find metabolic channels that drive the cells from proliferation to apoptosis or normal activity.

Summary

This discussion identified the huge expansion of genomic technology in the investigation of biopharmacotherapeutic targets that have been identified involving different levels and interacting signaling pathways.   There are several methods of analyzing gene expression, and a primary emphasis is given to combinations of mutations expressed in different cancer types.  There is a major hypothesis that expresses the need to focus on “central” “driver mutations” that correspond with the regulation of gene expression, cell proliferation, and cell metabolism.  What hasn’t been know is why drug resistance develops and whether the cellular migration and aerobic glycolysis can be redirected after cell metastasis occurs.

 

mutation in the matched nucleotides

mutation in the matched nucleotides

 

 

 

 

 

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A slight mutation in the matched nucleotides can lead to chromosomal aberrations and unintentional genetic rearrangement. (Photo credit: Wikipedia)

 

Phosphofructokinase mechanism

Phosphofructokinase mechanism

 

 

 

 

 

Deutsch: Regulation der Phosphofructokinase (Photo credit: Wikipedia)

Additional Related articles

 

 

Universal Language: The Pistoia Alliance Takes on Indescribable Biology

 

By Aaron Krol

July 18, 2014 | The Pistoia Alliance, founded after a meeting between members of Pfizer, AstraZeneca, Novartis and GlaxoSmithKline, has come to resemble a United Nations of the life sciences industry. Now in its fifth year, the Alliance’s membership has grown to include nearly all the largest pharma companies (Eli Lilly is the only holdout in the top ten) plus a huge assortment of publishers, IT vendors, small biotechs and academic groups. It makes for a complicated network of business partners and competitors, but they do have some basic needs in common. In particular, the Pistoia Alliance exists to build IT architectures that serve the precompetitive stages of research and development.

“The key to the Pistoia Alliance is that, as time has gone by, most companies have figured out that you can’t go it alone,” says Sergio Rotstein, the Director of Research Business Technologies at Pfizer and a member of the Alliance’s board of directors. “Even the tightest of companies has opened up its walls quite a bit to collaboration… The idea of me asking my buddy from Merck, how did you solve that problem, and by the way would you mind giving me the solution — ten years ago, that would have gotten me laughed out of the room.”

The Pistoia Alliance has previously sponsored new methods for querying databases and the scientific literature, and a more effective algorithm for compressing and sharing genetic sequencing data. Over the past year, another Pistoia project, HELM, has entered the public domain after gradual development by an assortment of Alliance members. An open source language and set of editing tools for working with large biomolecules, HELM has already become a foundational part of research in at least three large pharmaceutical companies.

At the Bio-IT World Best Practices Awards this April, the HELM project won the Pistoia Alliance a top prize in the category of Informatics. These awards recognize advances in information technology and good management strategies at all levels of the biomedical industry. While the Best Practices Awards always seek to highlight programs that could be widely replicated, Bio-IT World rarely has the opportunity to single out a project that has been adopted so quickly across so many organizations as the Pistoia Alliance’s efforts around HELM.

A Loss for Words

HELM addresses a problem at the root level of drug discovery. Pharmaceutical and biotech companies are looking at increasingly complex molecules in the search for new therapeutics, testing out RNA- and peptide-based compounds that tap directly into cellular pathways. The trouble is that these large molecules, which are often hybrids of RNA, amino acids and other chemical structures, are difficult to concisely describe, even when their structures are perfectly known. They are too large and ungainly to represent atom-by-atom, but not uniform enough to be reduced to nucleotides and peptide chains.

“There have been a number of ways to represent small molecules,” says Rotstein. “That’s been the bread and butter of a number of companies for a long time, and that’s the realm of cheminformatics. And there’s been a lot of methodology for dealing with sequence-based entities, like genes and proteins, which is the realm of bioinformatics. The issue is that the types of molecules that we are targeting fall in between these two.”

This isn’t just a semantic issue; not having a standard language for biomolecules has practical consequences. It’s hard to register these molecules in databases, and even harder to conduct searches for them or share their structures with collaborators. The problem has recently come to a head, as growing knowledge of interlocking cellular systems has led researchers to therapies that increasingly resemble the body’s own tangled biology. “It follows the natural progression of science itself,” says Rotstein. “The application of peptides with unnatural amino acids, and the area of antibody -drug conjugates, has been growing a great deal over the past few years. A lot of the companies that traditionally worked in the small molecule space, nowadays are looking for a diverse portfolio.”

In 2008, Rotstein was part of an oligonucleotide unit at Pfizer that set out to build a new language to describe the compounds it was working with. The language would be similar to the small molecule notation SMILES (the Simplified Molecular-Input Line-Entry System), which renders a chemical structure as a continuous string of characters, while using symbols from the ASCII alphabet to resolve properties like where bonds occur and how molecules branch. Instead of using atoms as the smallest units in the chain, however, much larger groups — monomers like nucleotides and amino acids — would receive short, unique IDs that could be strung together into polymers. The amino acid cysteine, for instance, could be represented simply as “C.” New monomers would be registered with new IDs in a central database, and every ID would be linked to a complete description in small molecule notation.

oligonucleotide conplex

oligonucleotide conplex

 

 

A complex oligonucleotide peptide conjugate, featuring amino acids, RNA, and other chemical structures. The molecule is rendered as both a monomer graph, and in HELM notation. Reproduced from the Journal of Chemical Information and Modeling with permission of the author

The language was called HELM, the Hierarchical Editing Language for Macromolecules: “hierarchical” because strings of monomers are built into simple polymers, which in turn are joined into complex polymers. HELM was easy to use and unambiguous, and was soon adopted in many more departments at Pfizer. For the first time, it was possible to quickly enter a new macromolecule in Pfizer’s registry, check for uniqueness, and receive a corporate ID to take the project forward.

A Living Language

At the same time that Rotstein’s team was developing HELM at Pfizer, other pharma companies and informatics vendors were struggling with the same problem. The software provider Accelrys (now BIOVIA), for instance, had modified the Molfile chemical table format to deal with hybrid macromolecules, in a system the company called the Self-Contained Sequence Representation (SCSR). There was a danger of proliferating standards, which would not only create redundant work at each company writing its own language, but also threaten the ability of these organizations to share information with each other.

Meanwhile, a member survey at the Pistoia Alliance flagged the representation of complex biomolecules as one of the industry’s top three non-competitive problems. Since Pfizer had already published a paper on HELM and built a software toolkit around the system, the company volunteered to make the entire program open source and continue its development with other members of the Alliance.

“We saw an opportunity for Pfizer,” says Rotstein. “If this did indeed become a standard, and the open source tools continued to evolve through contributions of the whole community, that would help us too.” All told, 24 companies sent volunteers to work on HELM, untangling the code from Pfizer’s internal systems, making it public, and extending the tools that serve the language.

The entire HELM project is now available on GitHub, and uses the permissive MIT open source license, which gives anyone the right to download and modify the code without requiring any contribution back to the project. That should encourage vendors to build commercial software on top of HELM, helping to foster compatibility across the industry.

The basic HELM toolkit includes search functions and uniqueness checks, as well as the HELM Editor, a platform for drawing chemical structures. The HELM Editor lets users plug in or draw monomers, then move up the scale to polymers made from those building blocks. It can be used simply as a translation tool, taking existing structures and giving them names in HELM notation, but Rotstein says it would also be a preferred platform for making new molecules from scratch.

 

HELM photo of siRNA

HELM photo of siRNA

 

 

 

A screenshot from the HELM Editor, showing a siRNA molecule under construction. Image credit: Pistoia Alliance

Since HELM was released to the public last year, development has continued at various partner organizations. Roche was one of the first adopters, and has been relentlessly adding functionality to the toolkit. “Roche created a custom antibody-drawing capability on top of the HELM Editor, and it’s truly phenomenal,” says Rotstein. “They are now putting the finishing touches on that, and as soon as they’re done, they are pushing it right back out into the open source.”

He adds that Pfizer plans to start using Roche’s antibody drawing tool itself. “That tool alone will probably return our entire investment on externalizing HELM.”

Most recently, this month the Pistoia Alliance released Exchangeable HEL M, another big push for interoperability. While some basic monomers, like the natural amino acids and nucleotides, have universal IDs in HELM, most monomer IDs are unique to each user, stored in an internal database. That’s a necessary feature to make HELM flexible to the needs of every user, but it means that most molecules only make sense in the context of the databases against which they were designed.

Exchangeable HELM provides a file format that includes both the larger HELM sequence of a macromolecule, and separately, the chemical structure of each monomer inside it. That makes it easy for collaborators — say, a large pharma company and a CRO hired for a specific project — to send molecular structures back and forth. Exchangeable HELM also offers a tool to “translate” between databases, if two organizations have different internal IDs for the same monomer.

The Lingua Franca

So far, Pfizer, Roche, and Lundbeck are the largest drug companies to switch their systems over to HELM, and Rotstein says a “robust pipeline of other companies” is preparing to adopt the language. Meanwhile, vendors that serve the drug industry are preparing for a widespread change. NextMove Software and ChemAxon are both working in HELM, and even BIOVIA, which plans to continue using SCSR internally, has made its systems compatible with HELM to more easily share large molecules with clients and partners.

The adoption of HELM will be buoyed by public resources in the life sciences that are turning to the language as the obvious choice for representing complex molecules. One big supporter is the European Bioinformatics Institute, whose ubiquitous ChEMBL database of chemical compounds will include HELM notations in its next release.

Increasingly, says Rotstein, the Pistoia Alliance is speaking of a HELM ecosystem. “We want to have content providers that have structures in HELM format. We want vendors whose software can read and write HELM. We want companies that use HELM as their standard, we want CROs that can use HELM to exchange information with those companies, and next on our list are downstream things like scientific journals and regulatory agencies.” Large publishers and regulators would be especially important adopters, because they are such frequent and public ports of call for companies sending macromolecular structures outside their walls. If the FDA or Nature Publishing Group began accepting HELM structures, it could be a major convenience when applying for clinical trials and publications. “It would be much easier to just send a file that says, ‘here’s exactly what my structure is,’” says Rotstein, “rather than having to verbally explain the structure.”

Having HELM in place as a widely-shared language could also benefit other Pistoia Alliance projects. For example, the Controlled Substance Compliant Services Project is currently building a database of compounds that are regulated or restricted in various countries around the world, so companies can quickly refer to the local legislation affecting compounds they want to work with. If large biomolecules are subject to regulations, HELM would be a convenient way to make those policies searchable.

Like other Pistoia Alliance initiatives, HELM is designed to run smoothly in the background. Defining the structure of macromolecules in a standard format, is not a process that should offer any company an edge in drug discovery, but a basic feature at the foundation of the life sciences. In an ideal world, says Rotstein, “this should be a non-issue. The ability to represent these molecules, and get them in and out of our system so we can store them, search them, and run calculations on them, should be trivial.”

 

Pathology Practiced Todat

How doctors group non Hodgkin lymphomas

There are many different types of non Hodgkin lymphoma. Doctors estimate that there are more than 60 subtypes. Understanding how the  different types of NHL are grouped, or classified, can be difficult. A variety of systems for classifying lymphomas have been used over the years. The latest is the World Health Organisation classification of 2008. We give a simple description of the groups on this page.

The pathologist will examine the cells to see

Grade of NHL

Doctors put non Hodgkin lymphomas into 2 groups depending on how quickly they are likely to grow and spread

  • Low grade (indolent) – these tend to grow very slowly
  • High grade (aggressive) – these tend to grow more quickly

The different grades of non Hodgkin lymphoma are treated in slightly different ways.

Type of white blood cell

One way of classifying NHL is by the type of white blood cells (lymphocytes) affected – B cells or T cells. Most people with NHL have B cell lymphomas.

What the lymphoma cells look like

Your doctor will be able to give your type of non Hodgkin lymphoma a name depending on the appearance of the lymphoma cells. These names are quite complicated. But they are useful to doctors because the different types can behave differently. Different treatments are used for the different types. So knowing the type helps the doctor know how to treat them. In the laboratory a pathologist looks at the cells to see if they are

  • Large or small
  • Grouped together in structures called follicles (follicular type) or spread out (diffuse type)

Low grade non Hodgkin lymphomas tend to have small cells that are grouped together.

Low grade (slowly growing) NHL

Low grade lymphomas tend to grow very slowly. Doctors call them indolent lymphomas. They include

Small lymphocytic lymphoma

Small lymphocytic lymphoma is also called chronic lymphocytic leukaemia (CLL). It makes up about 6 out of 100 lymphomas in the UK (6%). In theory, lymphoma is an illness that starts in the lymph nodes and leukaemia is an illness of the blood. But leukaemia and lymphoma have many similarities and often affect the body in similar ways. Chronic lymphocytic leukaemia is the term used for this condition if many of the abnormal cells are in the blood. Doctors call it small lymphocytic lymphoma when the disease involves the lymph nodes in particular.

The B-cell lymphomas are types of lymphoma affecting B cells. Lymphomas are “blood cancers” in the lymph glands. They develop more frequently in older adults and in immunocompromised individuals.

B-cell lymphomas include both Hodgkin’s lymphomas and most non-Hodgkins lymphomas. They are often divided into indolent (slow-growing) lymphomas and aggressive lymphomas. Indolent lymphomas respond rapidly to treatment and are kept under control (in remission) with long-term survival of many years, but are not cured. Aggressive lymphomas usually require intensive treatments, but have good prospects for a permanent cure.[1]

Prognosis and treatment depends on the specific type of lymphoma as well as the stage and grade. Treatment includes radiation and chemotherapy. Early-stage indolent B-cell lymphomas can often be treated with radiation alone, with long-term non-reoccurrence. Early-stage aggressive disease is treated with chemotherapy and often radiation, with a 70-90% cure rate.[1] Late-stage indolent lymphomas are sometimes left untreated and monitored until they progress. Late-stage aggressive disease is treated with chemotherapy, with cure rates of over 70%.[1]

Small cell Lymphocytic lymphoma (overlaps with Chronic lymphocytic leukemia)

Indolent NHL. These types of lymphoma grow very slowly. As a result, people with indolent NHL may not need to start treatment when it is first diagnosed. They are followed closely, and treatment is only started when they develop symptoms or the disease begins to change; this is called watchful waiting. When indolent lymphoma is located only in one area (called localized disease, stages I and II; see the Stages section), radiation therapy may eliminate the NHL.

 

Subtyping

In addition to determining if the NHL is indolent or aggressive and whether it is B-cell, T-cell, of NK-cell lymphoma, it is very important to determine the subtype of NHL because each subtype can behave differently and may require different treatments. There are about 35 subtypes of NHL.

Small lymphocytic lymphoma. This type of lymphoma is very closely related to a disease called B-cell chronic lymphocytic leukemia (CLL), and about 5% of people with NHL have this subtype. It is considered an indolent lymphoma. Patients with small lymphocytic lymphoma may receive a combination of chemotherapy, monoclonal antibodies, and/or radiation therapy, or they may be followed closely with watchful waiting.

Lymphoma – B cell neoplasms

Non-Hodgkin Lymphoma

Cytogenetics
Reviewer: Nikhil Sangle, M.D., University of Utah and ARUP Laboratories (see Reviewers page)
Revised: 17 February 2011, last major update February 2011
Copyright: (c) 2001-2011, PathologyOutlines.com, Inc.

List of translocations
==============================================

Relatively common translocations are listed below
See each topic for more complete lists:

● t(1;14)(p32;q11): SCL (tal-1) and T cell receptor delta/alpha; preT ALL (15-30%)
● deletion of 11q23: CLL (10-20%)
● t(11;14)(q13;q32): bcl1/PRAD1 and IgH; mantle cell lymphoma (90%), B cell prolymphocytic leukemia (20%), myeloma (3%)
● Trisomy 12: B-CLL (30%)
● deletion 13q14: B -CLL (25-50%)
● t(14;19)(q32;q13): IgH and bcl3; B-CLL
● t(16;22);(q23;q11): cmaf and Ig lambda; multiple myeloma
● Trisomy 18: common in marginal zone lymphoma, MALT type

 

Lymphoma – B cell neoplasms

B cell lymphoma subtypes

Chronic lymphocytic leukemia – features that differ from SLL
Reviewer: Nikhil Sangle, M.D., University of Utah and ARUP Laboratories (see Reviewers page)
Revised: 20 September 2012, last major update February 2011
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc

 

Terminology
==============================================

  • Leukemic disorder of CD5+ CD23+ tumor cells, usually B cell, that are small, round, low grade, with soccer ball appearance

Terminology
==============================================

  • Called CLL/chronic lymphocytic leukemia if leukemic involvement at diagnosis (5K or more of monoclonal B cell lymphocytosis per microliter)
    ● Less than 5K per microliter is termed monoclonal B lymphocytosis or possibly low stage CLL
    ● CLL with increased prolymphocytes (CLL/prolymphocytic leukemia): 10-55% prolymphocytes
    ● Prolymphocytic leukemia: >55% prolymphocytes

 

Lymphoma – B cell neoplasms

B cell lymphoma subtypes

Small lymphocytic lymphoma
Reviewer: Nikhil Sangle, M.D., University of Utah and ARUP Laboratories (see Reviewers page)
Revised: 6 February 2012, last major update February 2011
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc

 

Definition
==============================================

  • Common low grade B cell lymphoma with pseudofollicles composed of mature lymphocytes resembling soccer balls in peripheral blood; cells are CD5+, CD23+

Clinical features
==============================================

  • Usually older patients (median age 60 years), 2/3 male, with disease in bone marrow, lymph nodes, spleen, liver
    ● Often presents with leukemia, although patients may be asymptomatic
    ● SLL may progress to blood (leukemic) involvement, but if so, there is usually less leukocytosis than cases with initial diagnosis of CLL
    ● Almost all cases are B cell origin
    ● Associated with hypogammaglobulinemia, monoclonal immunoglobulin spikes in some, infections; also autoantibodies to red blood cells and platelets causing hemolytic anemia and thrombocytopenia
    ● Median survival 4-6 years; indolent unless it transforms

Poor prognostic factors
==============================================

  • 17p deletions, 11q22-23 deletion, non-mutated immunoglobulin genes, aberrant expression of CD2, CD7, CD10, CD13, CD33 or CD34 (Am J Clin Pathol 2003;119:824)

 

 

In 2013, the North American market was valued at $128.9 million and accounted for the largest share of the global digital pathology market, followed by Europe and Asia. The North American market is expected to grow at a healthy growth rate over the next five years. This high growth can be attributed to the favorable reimbursement scenario in the U.S. and the use of digital pathology to improve the quality of cancer diagnosis in Canada. However, lack of FDA approvals for digital pathology to be used for primary diagnosis acts as a major barrier for the North American market.

 

Other posts related to this discussion were published on this Open Source  Online Scientific Journal from Leaders in Pharmaceutical Business  Intelligence:

Big Data in Genomic Medicine, LHB
http://pharmaceuticalintelligence.com/2012/12/17/big-data-in-genomic-medicine/

A New Therapy for Melanoma, LHB
http://pharmaceuticalintelligence.com/2012/09/15/a-new-therapy-for-melanoma/

BRCA1 a tumour suppressor in breast and ovarian cancer – functions in transcription, ubiquitination and DNA repair,  S Saha
http://pharmaceuticalintelligence.com/2012/12/04/brca1-a-tumour-suppressor-in-breast-and-ovarian-cancer-functions-in-transcription-ubiquitination-and-dna-repair/

Judging ‘Tumor response’-there is more food for thought,  R Saxena
http://pharmaceuticalintelligence.com/2012/12/04/judging-the-tumor-response-there-is-more-food-for-thought/

Computational Genomics Center: New Unification of Computational Technologies at Stanford, A. Lev-Ari
http://pharmaceuticalintelligence.com/2012/12/03/computational-genomics-center-new-unification-of-computational-technologies-at-stanford/

Ovarian Cancer and fluorescence-guided surgery: A report, T.  Barliya
http://pharmaceuticalintelligence.com/2013/01/19/ovarian-cancer-and-fluorescence-guided-surgery-a-report/

Personalized medicine gearing up to tackle cancer ,  R. Saxena
http://pharmaceuticalintelligence.com/2013/01/07/personalized-medicine-gearing-up-to-tackle-cancer/

Exploring the role of vitamin C in Cancer therapy,   R. Saxena
http://pharmaceuticalintelligence.com/2013/01/15/exploring-the-role-of-vitamin-c-in-cancer-therapy/

Differentiation Therapy – Epigenetics Tackles Solid Tumors,    SJ Williams
http://pharmaceuticalintelligence.com/2013/01/03/differentiation-therapy-epigenetics-tackles-solid-tumors/

Mechanism involved in Breast Cancer Cell Growth: Function in Early Detection & Treatment,   A. Lev-Ari
http://pharmaceuticalintelligence.com/2013/01/17/mechanism-involved-in-breast-cancer-cell-growth-function-in-early-detection-treatment/

Personalized Medicine: Cancer Cell Biology and Minimally Invasive Surgery (MIS),  A. Lev-Ari
http://pharmaceuticalintelligence.com/2012/12/01/personalized-medicine-cancer-cell-biology-and-minimally-invasive-surgery-mis/

Role of Primary Cilia in Ovarian Cancer,  A. Awan
http://pharmaceuticalintelligence.com/2013/01/15/role-of-primary-cilia-in-ovarian-cancer-2/

The Molecular Pathology of Breast Cancer Progression,  T. Bailiya`
http://pharmaceuticalintelligence.com/2013/01/10/the-molecular-pathology-of-breast-cancer-progression/

Stanniocalcin: A Cancer Biomarker,   A. Awan
http://pharmaceuticalintelligence.com/2012/12/25/stanniocalcin-a-cancer-biomarker/

Nanotechnology, personalized medicine and DNA sequencing,  T. Barliya
http://pharmaceuticalintelligence.com/2013/01/09/nanotechnology-personalized-medicine-and-dna-sequencing/

Gastric Cancer: Whole-genome reconstruction and mutational signatures,  A. Lev-Ari
http://pharmaceuticalintelligence.com/2012/12/24/gastric-cancer-whole-genome-reconstruction-and-mutational-signatures-2/

Paradigm Shift in Human Genomics – Predictive Biomarkers and Personalized Medicine – Part 1, A. Lev-Ari
http://pharmaceuticalintelligence.com/2013/01/13/paradigm-shift-in-human-genomics-predictive-biomarkers-and-personalized-medicine-part-1/

LEADERS in Genome Sequencing of Genetic Mutations for Therapeutic Drug Selection in Cancer Personalized Treatment: Part 2,  A. Lev-Ari
http://pharmaceuticalintelligence.com/2013/01/13/leaders-in-genome-sequencing-of-genetic-mutations-for-therapeutic-drug-selection-in-cancer-personalized-treatment-part-2/

Personalized Medicine: An Institute Profile – Coriell Institute for Medical Research: Part 3, A. Lev-Ari
http://pharmaceuticalintelligence.com/2013/01/13/personalized-medicine-an-institute-profile-coriell-institute-for-medical-research-part-3/

The Consumer Market for Personal DNA Sequencing: Part 4, A. Lev-Ari

http://pharmaceuticalintelligence.com/2013/01/13/consumer-market-for-personal-dna-sequencing-part-4/

Harnessing Personalized Medicine for Cancer Management, Prospects of Prevention and Cure: Opinions of Cancer Scientific Leaders @http://pharmaceuticalintelligence.com   A. Lev-Ari
http://pharmaceuticalintelligence.com/2013/01/13/7000/

GSK for Personalized Medicine using Cancer Drugs needs Alacris systems biology model to determine the in silico effect of the inhibitor in its “virtual clinical trial”  A Lev-Ari
http://pharmaceuticalintelligence.com/2012/11/14/gsk-for-personalized-medicine-using-cancer-drugs-needs-alacris-systems-biology-model-to-determine-the-in-silico-effect-of-the-inhibitor-in-its-virtual-clinical-trial/

Recurrent somatic mutations in chromatin-remodeling and ubiquitin ligase complex genes in serous endometrial tumors,  S. Saha
http://pharmaceuticalintelligence.com/2012/11/19/recurrent-somatic-mutations-in-chromatin-remodeling-and-ubiquitin-ligase-complex-genes-in-serous-endometrial-tumors/

Metabolic drivers in aggressive brain tumors,  pkandala
http://pharmaceuticalintelligence.com/2012/11/11/metabolic-drivers-in-aggressive-brain-tumors/

Personalized medicine-based cure for cancer might not be far away, R. Saxena
http://pharmaceuticalintelligence.com/2012/11/20/personalized-medicine-based-cure-for-cancer-might-not-be-far-away/

Response to Multiple Cancer Drugs through Regulation of TGF-β Receptor Signaling: a MED12 Control, A. Lev-Ari
http://pharmaceuticalintelligence.com/2012/11/21/response-to-multiple-cancer-drugs-through-regulation-of-tgf-%CE%B2-receptor-signaling-a-med12-control/

Human Variome Project: encyclopedic catalog of sequence variants indexed to the human genome sequence,  A. Lev-Ari
http://pharmaceuticalintelligence.com/2012/11/24/human-variome-project-encyclopedic-catalog-of-sequence-variants-indexed-to-the-human-genome-sequence/

Prostate Cancer Cells: Histone Deacetylase Inhibitors Induce Epithelial-to-Mesenchymal Transition,  SJ Williams
http://pharmaceuticalintelligence.com/2012/11/30/histone-deacetylase-inhibitors-induce-epithelial-to-mesenchymal-transition-in-prostate-cancer-cells/

Tumor Imaging and Targeting: Predicting Tumor Response to Treatment: Where we stand?, R. Saxena
http://pharmaceuticalintelligence.com/2012/12/13/imaging-and-targeting-the-tumor-predicting-tumor-response-where-we-stand/

Nanotechnology: Detecting and Treating metastatic cancer in the lymph node, T. Barliya
http://pharmaceuticalintelligence.com/2012/12/19/nanotechnology-detecting-and-treating-metastatic-cancer-in-the-lymph-node/

Heroes in Medical Research: Barnett Rosenberg and the Discovery of Cisplatin, SJ Williams
http://pharmaceuticalintelligence.com/2013/01/12/heroes-in-medical-research-barnett-rosenberg-and-the-discovery-of-cisplatin/

Inspiration From Dr. Maureen Cronin’s Achievements in Applying Genomic Sequencing to Cancer Diagnostics,  A. Lev-Ari
http://pharmaceuticalintelligence.com/2013/01/10/inspiration-from-dr-maureen-cronins-achievements-in-applying-genomic-sequencing-to-cancer-diagnostics/

The “Cancer establishments” examined by James Watson, co-discoverer of DNA w/Crick, 4/1953,      A. Lev-Ari
http://pharmaceuticalintelligence.com/2013/01/09/the-cancer-establishments-examined-by-james-watson-co-discover-of-dna-wcrick-41953/

Nanotech Therapy for Breast Cancer. T. Barlyia
http://pharmaceuticalintelligence.com/2012/12/09/naotech-therapy-for-breast-cancer/

Dasatinib in Combination With Other Drugs for Advanced, Recurrent Ovarian Cancer,  pkandala
http://pharmaceuticalintelligence.com/2012/12/08/dasatinib-in-combination-with-other-drugs-for-advanced-recurrent-ovarian-cancer/

Squeezing Ovarian Cancer Cells to Predict Metastatic Potential: Cell Stiffness as Possible Biomarker, pkandala
http://pharmaceuticalintelligence.com/2012/12/08/squeezing-ovarian-cancer-cells-to-predict-metastatic-potential-cell-stiffness-as-possible-biomarker/

Hypothesis – following on James Watson,  LHB

http://pharmaceuticalintelligence.com/2013/01/27/novel-cancer-h…ts-are-harmful/

Otto Warburg, A Giant of Modern Cellular Biology, LHB
http://pharmaceuticalintelligence.com/2012/11/02/otto-warburg-a-giant-of-modern-cellular-biology/

Is the Warburg Effect the cause or the effect of cancer: A 21st Century View?  LHB
http://pharmaceuticalintelligence.com/2012/10/17/is-the-warburg-effect-the-cause-or-the-effect-of-cancer-a-21st-century-view/

Remembering a Great Scientist among Mentors,  LHB
http://pharmaceuticalintelligence.com/2013/01/26/remembering-a-great-scientist-among-mentors/

Portrait of a great scientist and mentor: Nathan Oram Kaplan,   LHB
http://pharmaceuticalintelligence.com/2013/01/26/portrait-of-a-great-scientist-and-mentor-nathan-oram-kaplan/

Predicting Tumor Response, Progression, and Time to Recurrence, LHB
http://pharmaceuticalintelligence.com/2012/12/20/predicting-tumor-response-progression-and-time-to-recurrence/

Directions for genomics in personalized medicine,   LHB
http://pharmaceuticalintelligence.com/2013/01/27/directions-for-genomics-in-personalized-medicine/

How mobile elements in “Junk” DNA promote cancer. Part 1: Transposon-mediated tumorigenesis,  Sjwilliams
http://pharmaceuticalintelligence.com/2012/10/31/how-mobile-elements-in-junk-dna-prote-cacner-part1-transposon-mediated-tumorigenesis/

Novel Cancer Hypothesis Suggests Antioxidants Are Harmful, LHB
http://pharmaceuticalintelligence.com/2013/01/27/novel-cancer-hypothesis-suggests-antioxidants-are-harmful/

Mitochondria: Origin from oxygen free environment, role in aerobic glycolysis, metabolic adaptation,  LHB
http://pharmaceuticalintelligence.com/2012/09/26/mitochondria-origin-from-oxygen-free-environment-role-in-aerobic-glycolysis-metabolic-adaptation/

Advances in Separations Technology for the “OMICs” and Clarification of Therapeutic Targets, LHB
http://pharmaceuticalintelligence.com/2012/10/22/advances-in-separations-technology-for-the-omics-and-clarification-of-therapeutic-targets/

Cancer Innovations from across the Web, LHB
http://pharmaceuticalintelligence.com/2012/11/02/cancer-innovations-from-across-the-web/

Mitochondrial Damage and Repair under Oxidative Stress, LHB
http://pharmaceuticalintelligence.com/2012/10/28/mitochondrial-damage-and-repair-under-oxidative-stress/

Mitochondria: More than just the “powerhouse of the cell” R. Saxena
http://pharmaceuticalintelligence.com/2012/07/09/mitochondria-more-than-just-the-powerhouse-of-the-cell/

Mitochondria and Cancer: An overview of mechanisms, R. Saxena
http://pharmaceuticalintelligence.com/2012/09/01/mitochondria-and-cancer-an-overview/

Mitochondrial fission and fusion: potential therapeutic targets?  R. Saxena
http://pharmaceuticalintelligence.com/2012/10/31/mitochondrial-fission-and-fusion-potential-therapeutic-target/

Mitochondrial mutation analysis might be “1-step” away, R. Saxena
http://pharmaceuticalintelligence.com/2012/08/14/mitochondrial-mutation-analysis-might-be-1-step-away/

β Integrin emerges as an important player in mitochondrial dysfunction associated Gastric Cancer,       R. Saxena
http://pharmaceuticalintelligence.com/2012/09/10/%CE%B2-integrin-emerges-as-an-important-player-in-mitochondrial-dysfunction-associated-gastric-cancer/

mRNA interference with cancer expression, LHB
http://pharmaceuticalintelligence.com/2012/10/26/mrna-interference-with-cancer-expression/

What can we expect of tumor therapeutic response?  LHB
http://pharmaceuticalintelligence.com/2012/12/05/what-can-we-expect-of-tumor-therapeutic-response/

Expanding the Genetic Alphabet and linking the genome to the metabolome, LHB
http://pharmaceuticalintelligence.com/2012/09/24/expanding-the-genetic-alphabet-and-linking-the-genome-to-the-metabolome/

Breast Cancer, drug resistance, and biopharmaceutical targets, LHB
http://pharmaceuticalintelligence.com/2012/09/18/breast-cancer-drug-resistance-and-biopharmaceutical-targets/

Breast Cancer: Genomic Profiling to Predict Survival: Combination of Histopathology and Gene Expression Analysis, A. Lev-Ari
http://pharmaceuticalintelligence.com/2012/12/24/breast-cancer-genomic-profiling-to-predict-survival-combination-of-histopathology-and-gene-expression-analysis/

Ubiquinin-Proteosome pathway, autophagy, the mitochondrion, proteolysis and cell apoptosis,   LHB
http://pharmaceuticalintelligence.com/2012/10/30/ubiquinin-proteosome-pathway-autophagy-the-mitochondrion-proteolysis-and-cell-apoptosis/

Identification of Biomarkers that are Related to the Actin Cytoskeleton, LHB
http://pharmaceuticalintelligence.com/2012/12/10/identification-of-biomarkers-that-are-related-to-the-actin-cytoskeleton/

Nitric Oxide has a ubiquitous role in the regulation of glycolysis -with a concomitant influence on mitochondrial function, LHB
http://pharmaceuticalintelligence.com/2012/09/16/nitric-oxide-has-a-ubiquitous-role-in-the-regulation-of-glycolysis-with-a-concomitant-influence-on-mitochondrial-function/

Genomic Analysis: FLUIDIGM Technology in the Life Science and Agricultural Biotechnology,  A. Lev-Ari http://pharmaceuticalintelligence.com/2012/08/22/genomic-analysis-fluidigm-technology-in-the-life-science-and-agricultural-biotechnology/

Nanotechnology: Detecting and Treating metastatic cancer in the lymph node, T. Barliya
http://pharmaceuticalintelligence.com/2012/12/19/nanotechnology-detecting-and-treating-metastatic-cancer-in-the-lymph-node/

 

Reporter: Aviva Lev-Ari, PhD, RN 

Crohn’s disease driven by inflammation – not genetics, reports study   Aug. 15, 2012

Inflammation — not genetic susceptibility —

  • drives the growth of intestinal bacteria and invasive E. coli linked to Crohn’s disease (CD), reports a new Cornell study.

Scientists have long wondered about the role of bacteria in CD. Recent studies have shown marked changes in the composition of the intestinal bacteria in people

  • with CD, leading researchers to ask: Are microbial abnormalities a direct consequence of genetic abnormalities linked to Crohn’s and precede and initiate inflammation, or does intestinal inflammation bring on the bugs?

This study also reports that a common therapy directed against intestinal inflammation decreases dysbiosis. In addition, the study found that

  • the lack of a receptor that helps recruit T cells, which are needed for cell-mediated immunity, to the gut also decreases inflammation and dysbiosis, offering a new option for therapeutic intervention.Inflammation, in fact,
  • drives microbial imbalances (dysbiosis) and

the proliferation of a specific type of E. coli that is adherent, invasive and found in the ileum, reported Cornell researchers July 31 in PLoS (7[7]).

CD is a chronic debilitating inflammatory bowel disease that involves a complex interaction of

  • host genes,
  • the immune system,
  • the intestinal microbiome and
  • the environment.

To mirror the complex nature of the disease, Simpson’s team designed a study that

  • incorporated inflammatory triggers related to relapse of CD and ileal inflammation.

The team focused on ileal dysbiosis, which is prevalent in 70 percent of CD cases and

  • used a variety of contemporary techniques to generate a comprehensive picture of the composition and spatial distribution of the ileal microbiome.

Particular attention was paid to pinpointing

  1. the number,
  2. pathotype and
  3. location

of E. coli associated with intestinal inflammation in people, dogs and mice.

The findings demonstrate that

  • inflammation drives ileal dysbiosis and proliferation of CD-associated adherent invasive E. coli.
  1. the host genotype and therapeutically blocking inflammation both impact the onset and extent of ileal dysbiosis.

The investigation leveraged the knowledge and resources of researchers in the labs of Erik Denker, Dwight Bowman and Sean McDonough labs. Building on findings in patients with Crohn’s disease evaluated by Dr. Ellen Scherl’s group at Weill Cornell Medical College, this collaboration shed new light on this debilitating disease.

This work was supported by NewYork-Presbyterian Hospital/Weill Cornell Medical Center, the Jill Roberts Center for Inflammatory Bowel Disease and the National Institutes of Health.

http://www.news.cornell.edu/stories/Aug12/Inflammation.html 

 

Functional Proteomics Related to Energy Metabolism of Synaptosomes

from iTRAQ-Based Quantitative Proteomics Analysis Revealed Alterations of Carbohydrate Metabolism Pathways and Mitochondrial Proteins in a Male Sterile Cybrid Pummelo

Bei-Bei Zheng †, Yan-Ni Fang †, Zhi-Yong Pan †, Li Sun †, Xiu-Xin Deng †, Jude W. Grosser ‡, andWen-Wu Guo *

 Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan 430070, China
 Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, Florida 33850, United States

  1. Proteome Res., May 13, 201413(6), pp 2998–3015 http://dx.doi.org:/10.1021/pr500126g

 

Plant Biochemistry

Comprehensive and quantitative proteomic information on citrus floral bud is significant for understanding

  • male sterility of the cybrid pummelo (G1+HBP) with nuclear genome of HBP and foreign mitochondrial genome of G1.

Scanning electron microscopy and transmission electron microscopy analyses of the anthers showed that

  • the development of pollen wall in G1+HBP was severely defective with a lack of exine and sporopollenin formation.

Proteomic analysis was used to identify the differentially expressed proteins between male sterile G1+HBP and fertile type (HBP)

  • with the aim to clarify their potential roles in another development and male sterility.

On the basis of iTRAQ quantitative proteomics, we identified 2235 high-confidence protein groups, 666 of which showed

  • differentially expressed profiles in one or more stages.

Proteins up- or down-regulated in G1+HBP were mainly involved in

  1. carbohydrate and energy metabolism (e.g., pyruvate dehydrogenase, isocitrate dehydrogenase, ATP synthase, and malate dehydrogenase),
  2. nucleotide binding (RNA-binding proteins),
  3. protein synthesis and degradation (e.g., ribosome proteins and proteasome subunits).

Additionally, the proteins located in mitochondria also showed changed expression patterns. These findings provide a valuable inventory of proteins involved in floral bud development and contribute to elucidate the mechanism of cytoplasmic male sterility in the cybrid pummelo.

Keywords: cybridmale sterilitymitochondriaproteometranscriptomeprimary metabolites

 

BIMSB Proteomics / Metabolomics

Overview

Within the past decades biochemical data of single processes, metabolic and signaling pathways were collected and advances in technology

  • led to improvements of sensitivity and resolution of bioanalytical techniques.

These achievements build the bases for the so called ‘genome wide biochemistry’. High throughput techniques are the tool for large scale ‘-omics’ studies

  • allowing the obtainment of a nearly complete picture of a determinate cell state, concerning its metabolites, proteins and transcripts.

However, a single level study of a living organism cannot give a complete understanding of the mechanisms regulating biological functions.
The integration of transcriptomics, proteomics and metabolomics data with existing knowledge allows connecting biological processes which were treated as independent so far. In this context the aim of our group is

  1. to apply metabolomics and proteomics techniques for absolute quantification and
  2. to analyze turnover rates of proteins and metabolites using stable isotopes. In addition,
  3. the development of data analysis workflows and integrative strategies are in the focus of our interest.

The central metabolism is the principal source of energy and building blocks for cell growth and survival. It is highly flexible and adjusted to the physiological program of the cell, organ and organism. In a healthy state

  • cellular metabolism is tightly regulated to guarantee physiological function but also efficient usage of available recourses.

Metabolic dys-regulations are cause or response to many diseases. An impaired metabolic activity can lead to

  • the loss of the physiological activity, cell damage or inefficient substrate usage. However,
  • the underlying mechanisms leading to metabolic dys-functions are not well understood.

The regulation of metabolism is complex, because

  • it acts at all biological layers – transcriptional, translational and post-translational.

Thus the metabolic activity of a cell, organ or organism inherits the information of regulatory layers in a multidimensional manner. I guess only the use of integrative mathematical approaches will enable us to decode such complex information.

In this regard, decoding the metabolic composition of biofluids e.g. blood serum

  • may allow to determine a systems status, to identify diseases, predict drug responsiveness and to follow the success of medical treatments. This is a step towards personalized medicine.

http://www.mdc-berlin.de/20902775/en/research/core_facilities/cf_massspectromety_bimsb

 

Coordination of bacterial proteome with metabolism by cyclic AMP signaling

Conghui You, Hiroyuki Okano, Sheng Hui, Zhongge Zhang, Minsu Kim, et al.

Nature  (15 August 2013);  500, 301–306  http://dx.doi.org:/10.1038/nature12446

 

The cyclic AMP (cAMP)-dependent catabolite repression effect in Escherichia coli is among the most intensely studied regulatory processes in biology. However,

  • the physiological function(s) of cAMP signalling and its molecular triggers remain elusive.

Here we use a quantitative physiological approach to show that

  • cAMP signalling tightly coordinates the expression of catabolic proteins with biosynthetic and ribosomal proteins,
  • in accordance with the cellular metabolic needs during exponential growth.

The expression of carbon catabolic genes increased linearly

  • with decreasing growth rates upon limitation of carbon influx,
  • but decreased linearly with decreasing growth rate upon limitation of nitrogen or sulphur influx.

In contrast, the expression of biosynthetic genes showed the opposite linear growth-rate dependence as the catabolic genes. A coarse-grained mathematical model provides a quantitative framework for understanding and predicting

  • gene expression responses to catabolic and anabolic limitations.

A scheme of integral feedback control featuring the inhibition of cAMP signalling by metabolic precursors is proposed and validated. These results reveal a key physiological role of

  • cAMP-dependent catabolite repression: to ensure that proteomic resources are spent on distinct metabolic sectors as needed
  • in different nutrient environments.

Our findings underscore the power of quantitative physiology in unravelling the underlying functions of complex molecular signalling networks.

 

Exosomes from bone marrow mesenchymal stem cells contain a microRNA that promotes dormancy in metastatic breast cancer cells

Makiko Ono1, Nobuyoshi Kosaka1, Naoomi Tominaga1, Yusuke Yoshioka1, Fumitaka Takeshita1,  et al.
Sci. Signal., July 2014;  7(332),  p. ra63    http://dx.doi.org:/10.1126/scisignal.2005231

Breast cancer patients often develop metastatic disease years after resection of the primary tumor. The patients are asymptomatic because the disseminated cells appear to become dormant and are undetectable. Because the proliferation of these cells is slowed, dormant cells are often unresponsive to traditional chemotherapies that exploit the rapid cell cycling of most cancer cells. We generated a bone marrow–metastatic human breast cancer cell line (BM2) by tracking and isolating fluorescent-labeled MDA-MB-231 cells that disseminated to the bone marrow in mice. Coculturing BM2 cells with bone marrow mesenchymal stem cells (BM-MSCs) isolated from human donors revealed that BM-MSCs suppressed the proliferation of BM2 cells, decreased the abundance of stem cell–like surface markers, inhibited their invasion through Matrigel Transwells, and decreased their sensitivity to docetaxel, a common chemotherapy agent. Acquisition of these dormant phenotypes in BM2 cells was also observed by culturing the cells in BM-MSC–conditioned medium or with exosomes isolated from BM-MSC cultures, which were taken up by BM2 cells. Among various microRNAs (miRNAs) increased in BM-MSC–derived exosomes compared with those from adult fibroblasts, overexpression of miR-23b in BM2 cells induced dormant phenotypes through the suppression of a target gene, MARCKS, which encodes a protein that promotes cell cycling and motility. Metastatic breast cancer cells in patient bone marrow had increased miR-23b and decreasedMARCKS expression. Together, these findings suggest that exosomal transfer of miRNAs from the bone marrow may promote breast cancer cell dormancy in a metastatic niche.

Citation:

  1. Ono, N. Kosaka, N. Tominaga, Y. Yoshioka, F. Takeshita, R. Takahashi, M. Yoshida, H. Tsuda, K. Tamura, and T. Ochiya, Exosomes from bone marrow mesenchymal stem cells contain a microRNA that promotes dormancy in metastatic breast cancer cells. Sci. Signal.7, ra63 (2014).


Poly(ADP-ribose) polymerase-dependent energy depletion occurs through inhibition of glycolysis.

Andrabi SA1Umanah GK2Chang C3Stevens DA4Karuppagounder SS2Gagné JP5Poirier GG5Dawson VL6Dawson TM7.

Proc Natl Acad Sci U S A. 2014 Jul 15; 111(28):10209-14. http://dx.doi.org:/10.1073/pnas.1405158111

 

Excessive poly(ADP-ribose) (PAR) polymerase-1 (PARP-1) activation kills cells via a cell-death process designated “parthanatos” in which PAR induces the mitochondrial release and nuclear translocation of apoptosis-inducing factor to initiate chromatinolysis and cell death. Accompanying the formation of PAR are the reduction of cellular NAD(+) and energetic collapse, which have been thought to be caused by the consumption of cellular NAD(+) by PARP-1. Here we show that the bioenergetic collapse following PARP-1 activation is not dependent on NAD(+) depletion. Instead PARP-1 activation initiates glycolytic defects via PAR-dependent inhibition of hexokinase, which precedes the NAD(+) depletion in N-methyl-N-nitroso-N-nitroguanidine (MNNG)-treated cortical neurons. Mitochondrial defects are observed shortly after PARP-1 activation and are mediated largely through defective glycolysis, because supplementation of the mitochondrial substrates pyruvate and glutamine reverse the PARP-1-mediated mitochondrial dysfunction. Depleting neurons of NAD(+) with FK866, a highly specific noncompetitive inhibitor of nicotinamide phosphoribosyltransferase, does not alter glycolysis or mitochondrial function. Hexokinase, the first regulatory enzyme to initiate glycolysis by converting glucose to glucose-6-phosphate, contains a strong PAR-binding motif. PAR binds to hexokinase and inhibits hexokinase activity in MNNG-treated cortical neurons. Preventing PAR formation with PAR glycohydrolase prevents the PAR-dependent inhibition of hexokinase. These results indicate that bioenergetic collapse induced by overactivation of PARP-1 is caused by PAR-dependent inhibition of glycolysis through inhibition of hexokinase.

PMID:24987120     PMCID: PMC4104885   [Available on 2015/1/15]

 

Aim24 stabilizes respiratory chain supercomplexes and is required for efficient respiration

Deckers M1Balleininger M1Vukotic M1Römpler K1Bareth B1Juris L1Dudek J2.

FEBS Lett. 2014 Jun 10. pii: S0014-5793(14)00458-X. http://dx.doi.org:/10.1016/j.febslet.2014.06.006

 

The mitochondrial respiratory chain is essential for the conversion of energy derived from the oxidation of metabolites into the membrane potential, which drives the synthesis of ATP. The electron transporting complexes bc1 complex and the cytochrome c oxidase assemble into large supercomplexes, allowing efficient energy transduction. Currently, we have only limited information about what determines the structure of the supercomplex. Here, we characterize Aim24 in baker’s yeast as a protein, which is integrated in the mitochondrial inner membrane and is required for the structural integrity of the supercomplex. Deletion of AIM24 strongly affects activity of the respiratory chain and induces a growth defect on non-fermentable medium. Our data indicate that Aim24 has a function in stabilizing the respiratory chain supercomplexes.    PMID: 24928273

KEYWORDS: Aim24; Membrane protein; Metabolism; Mitochondria; Respiration; Supercomplex

 

 

 

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Overview of Posttranslational Modification (PTM)

Curator:  Larry H. Bernstein, MD, FCAP

UPDATED on 4/1/2022

Cited in

https://www.beckman.com/resources/sample-type/bio-molecules/post-translational-modification

 

 

This is the second discussion of a several part series leading from the genome, to protein synthesis (1), posttranslational modification of proteins (2), examples of protein effects on metabolism and signaling pathways (3), and leading to disruption of signaling pathways in disease (4), and effects leading to mutagenesis.

1.  A Primer on DNAand DNA Replication

2. Overview of translational medicine

3. Genes, proteomes, and their interaction

4. Regulation of somatic stem cell Function

5.  Proteomics – The Pathway to Understanding and Decision-making in Medicine

6.  Genomics, Proteomics and standards

7.  Long Non-coding RNAs Can Encode Proteins After All

8.  Proteins and cellular adaptation to stress

9.  Loss of normal growth regulation

 

Posttranslational modification is a step in protein biosynthesis. Proteins are created by ribosomes translating mRNA into polypeptide chains. These polypeptide chains undergo
PTM before becoming the mature protein product.

Protein phosphorylation is one type of post-translational modification. Wikipedia

Explore: Phosphorylation

Glycosylation is a form of co-translational and post-translational modification. Wikipedia

Explore: Glycosylation

Acetylation occurs as a co-translational and post-translational modification of proteins, for example, histones, p53, and tubulins.

 

Post-Translational Modifications
As noted above, the large number of different PTMs precludes a thorough review of all possible protein modifications. Therefore, this overview only touches on a small number of the most common types of PTMs studied in protein research today. Furthermore, greater focus is placed on phosphorylation, glycosylation and ubiquitination, and therefore these PTMs are described in greater detail on pages dedicated to the respective PTM.
PhosphorylationReversible protein phosphorylation, principally on serine, threonine or tyrosine residues, is one of the most important and well-studied post-translational modifications. Phosphorylation plays critical roles in the regulation of many cellular processes including cell cycle, growth, apoptosis and signal transduction pathways.
GlycosylationProtein glycosylation is acknowledged as one of the major post-translational modifications, with significant effects on protein folding, conformation, distribution, stability and activity. Glycosylation encompasses a diverse selection of sugar-moiety additions to proteins that ranges from simple monosaccharide modifications of nuclear transcription factors to highly complex branched polysaccharide changes of cell surface receptors. Carbohydrates in the form of aspargine-linked (N-linked) or serine/threonine-linked (O-linked) oligosaccharides are major structural components of many cell surface and secreted proteins.
UbiquitinationUbiquitin is an 8-kDa polypeptide consisting of 76 amino acids that is appended to lysine in target proteins via the C-terminal glycine of ubiquitin. A ubiquitin polymer is formed after  initial monoubiquitination. Polyubiquitinated proteins are degraded recycling the ubiquitin.
S-NitrosylationNitric oxide (NO) is produced by three isoforms of nitric oxide synthase (NOS) and is a chemical messenger that reacts with free cysteine residues to form S-nitrothiols (SNOs). S-nitrosylation is a critical PTM used by cells to stabilize proteins, regulate gene expression and provide NO donors, and the generation, localization, activation and catabolism of SNOs are tightly regulated.S-nitrosylation is a reversible reaction, and SNOs have a short half life in the cytoplasm because of the host of reducing enzymes, including glutathione (GSH) and thioredoxin, that denitrosylate proteins. Therefore, SNOs are often stored in membranes, vesicles, the interstitial space and lipophilic protein folds to protect them from denitrosylation (5). For example, caspases, which mediate apoptosis, are stored in the mitochondrial intermembrane space as SNOs. In response to extra- or intracellular cues, the caspases are released into the cytoplasm, and the highly reducing environment rapidly denitrosylates the proteins, resulting in caspase activation and the induction of apoptosis.Only specific cysteine residues are S-nitrosylated. Proteins may contain multiple cysteines and due to the labile nature of SNOs, S-nitrosylated cysteines can be difficult to detect and distinguish from non-S-nitrosylated amino acids. The biotin switch assay, developed by Jaffrey et al., is a common method of detecting SNOs, and the steps of the assay are listed below (6):

  • All free cysteines are blocked.
  • All remaining cysteines (presumably only those that are denitrosylated) are denitrosylated.
  • The now-free thiol groups are then biotinylated.
  • Biotinylated proteins are detected by SDS-PAGE and Western blot analysis or mass spectrometry (7).
MethylationThe transfer of one-carbon methyl groups to nitrogen or oxygen (N- and O-methylation, respectively) to amino acid side chains increases the hydrophobicity of the protein and can neutralize a negative amino acid charge when bound to carboxylic acids. Methylation is mediated by methyltransferases, and S-adenosyl methionine (SAM) is the primary methyl group donor.Methylation occurs so often that SAM has been suggested to be the most-used substrate in enzymatic reactions after ATP (4). Additionally, while N-methylation is irreversible, O-methylation is potentially reversible. Methylation is a well-known mechanism of epigenetic regulation, as histone methylation and demethylation influences the availability of DNA for transcription.
N-AcetylationN-acetylation, or the transfer of an acetyl group to nitrogen, occurs in almost all eukaryotic proteins through both irreversible and reversible mechanisms. N-terminal acetylation requires the cleavage of the N-terminal methionine by methionine aminopeptidase (MAP) before replacing the amino acid with an acetyl group from acetyl-CoA by N-acetyltransferase (NAT) enzymes. This type of acetylation is co-translational, in that N-terminus is acetylated on growing polypeptide chains that are still attached to the ribosome.Acetylation at the ε-NH2 of lysine (termed lysine acetylation) on histone N-termini is a common method of regulating gene transcription. Histone acetylation is a reversible event that reduces chromosomal condensation to promote transcription, and the acetylation of these lysine residues is regulated by transcription factors that contain histone acetyletransferase (HAT) activity. While transcription factors with HAT activity act as transcription co-activators, histone deacetylase (HDAC) enzymes are co-repressors that reverse the effects of acetylation by reducing the level of lysine acetylation and increasing chromosomal condensation.Sirtuins (silent information regulator) are a group of NAD-dependent deacetylases that target histones. As their name implies, they maintain gene silencing by hypoacetylating histones and have been reported to aid in maintaining genomic stability (8).Cytoplasmic proteins may also be acetylated, and therefore acetylation seems to play a greater role in cell biology than simply transcriptional regulation (9). Furthermore, crosstalk between acetylation and other post-translational modifications, including phosphorylation, ubiquitination and methylation, can modify the biological function of the acetylated protein (10).
LipidationLipidation is a method to target proteins to membranes in organelles (endoplasmic reticulum [ER], Golgi apparatus, mitochondria), vesicles (endosomes, lysosomes) and the plasma membrane. The four types of lipidation are:

  • C-terminal glycosyl phosphatidylinositol (GPI) anchor
  • N-terminal myristoylation
  • S-myristoylation
  • S-prenylation

Each type of modification gives proteins distinct membrane affinities, although all types of lipidation increase the hydrophobicity of a protein and thus its affinity for membranes. The different types of lipidation are not mutually exclusive, in that two or more lipids can be attached to a given protein.

GPI anchors tether cell surface proteins to the plasma membrane. These hydrophobic moieties are prepared in the ER, where they are then added to the nascent protein en bloc. GPI-anchored proteins are often localized to cholesterol- and sphingolipid-rich lipid rafts, which act as signaling platforms on the plasma membrane.

N-myristoylation
is a method to give proteins a hydrophobic handle for membrane localization. The myristoyl group is a 14-carbon saturated fatty acid (C14), which gives the protein sufficient hydrophobicity and affinity for membranes, but not enough to permanently anchor the protein in the membrane. N-myristoylation can therefore act as a conformational localization switch, in which protein conformational changes influence the availability of the handle for membrane attachment.

N-myristoylation, facilitated specifically by N-myristoyltransferase (NMT), uses myristoyl-CoA to attach the myristoyl group to the N-terminal glycine. This PTM requires methionine cleavage prior to addition of the myristoyl group because methionine is the N-terminal amino acid of all eukaryotic proteins.

 S-palmitoylation adds a C16 palmitoyl group from palmitoyl-CoA to the thiolate side chain of cysteine residues via palmitoyl acyl transferases (PATs). Because of the longer hydrophobic group, this anchor can permanently anchor the protein to the membrane. S-palmitoylation is used as an on/off switch to regulate membrane localization.

S-prenylation covalently adds a farnesyl (C15) or geranylgeranyl (C20) group to specific cysteine residues within 5 amino acids from the C-terminus via farnesyl transferase (FT) or geranylgeranyl transferases (GGT I and II). All members of the Ras superfamily are prenylated. These proteins have specific 4-amino acid motifs at the C-terminus that determine the type of prenylation at single or dual cysteines. Prenylation occurs in the ER and is often part of a stepwise process of PTMs that is followed by proteolytic cleavage by Rce1 and methylation by isoprenyl cysteine methyltransferase (ICMT).

ProteolysisPeptide bonds are indefinitely stable under physiological conditions, and therefore cells require some mechanism to break these bonds. Proteases comprise a family of enzymes that cleave the peptide bonds of proteins and are critical in antigen processing, apoptosis, surface protein shedding and cell signaling.Degradative proteolysis is critical to remove unassembled protein subunits and misfolded proteins and to maintain protein concentrations at homeostatic concentrations.Proteolysis is a thermodynamically favorable and irreversible reaction. Therefore, protease activity is tightly regulated to avoid uncontrolled proteolysis through temporal and/or spatial control mechanisms including regulation by cleavage in cis or trans and compartmentalization (e.g., proteasomes, lysosomes).

 

The diverse family of proteases can be classified by the site of action, such as aminopeptidases and carboxypeptidase, which cleave at the amino or carboxy terminus of a protein, respectively. Another type of classification is based on the active site groups of a given protease that are involved in proteolysis. Based on this classification strategy, greater than 90% of known proteases fall into one of four categories as follows:

  • Serine proteases
  • Cysteine proteases
  • Aspartic acid proteases
  • Zinc metalloproteases
References
  1. International Human Genome Sequencing Consortium (2004) Finishing the euchromatic sequence of the human genome. Nature. 431, 931-45.
  2. Jensen O. N. (2004) Modification-specific proteomics: Characterization of post-translational modifications by mass spectrometry. Curr Opin Chem Biol. 8, 33-41.
  3. Ayoubi T. A. and Van De Ven W. J. (1996) Regulation of gene expression by alternative promoters. FASEB J. 10, 453-60.
  4. Walsh C. (2006) Posttranslational modification of proteins : Expanding nature’s inventory. Englewood, Colo.: Roberts and Co. Publishers. xxi, 490 p. p.
  5. Gaston B. M. et al. (2003) S-nitrosylation signaling in cell biology. Mol Interv. 3, 253-63.
  6. Jaffrey S. R. and Snyder S. H. (2001) The biotin switch method for the detection of S-nitrosylated proteins. Sci STKE. 2001, pl1.
  7. Han P. and Chen C. (2008) Detergent-free biotin switch combined with liquid chromatography/tandem mass spectrometry in the analysis of S-nitrosylated proteins. Rapid Commun Mass Spectrom. 22, 1137-45.
  8. Imai S. et al. (2000) Transcriptional silencing and longevity protein SIR2 is an NAD-dependent histone deacetylase. Nature. 403, 795-800.
  9. Glozak M. A. et al. (2005) Acetylation and deacetylation of non-histone proteins. Gene. 363, 15-23.
  10. Yang X. J. and Seto E. (2008) Lysine acetylation: Codified crosstalk with other posttranslational modifications. Mol Cell. 31, 449-61

 

Protein phosphorylation

From Wikipedia, the free encyclopedia

Protein phosphorylation is a post-translational modification of proteins in which a serine, a threonine or a tyrosine residue is phosphorylated by a protein kinase by the addition of a covalently bound phosphate group. Regulation of proteins by phosphorylation is one of the most common modes of regulation of protein function, and is often termed “phosphoregulation”. In almost all cases of phosphoregulation, the protein switches between a phosphorylated and an unphosphorylated form, and one of these two is an active form, while the other one is an inactive form.

Functions of phosphorylation[edit]

In some reactions, the purpose of phosphorylation is to “activate” or “volatize” a molecule, increasing its energy so it is able to participate in a subsequent reaction with a negativefree-energy change. All kinases require a divalent metal ion such as Mg2+ or Mn2+ to be present, which stabilizes the high-energy bonds of the donor molecule (usually ATP or ATP derivative) and allows phosphorylation to occur.

In other reactions, phosphorylation of a protein substrate can inhibit its activity (as when AKT phosphorylates the enzyme GSK-3). One common mechanism for phosphorylation-mediated enzyme inhibition was demonstrated in the tyrosine kinase called “src” (pronounced “sarc”, see: Src (gene)). When src is phosphorylated on a particular tyrosine, it folds on itself, and thus masks its own kinase domain, and is thus turned “off”.

In still other reactions, phosphorylation of a protein causes it to be bound to other proteins which have “recognition domains” for a phosphorylated tyrosineserine, or threoninemotif. As a result of binding a particular protein, a distinct signaling system may be activated or inhibited.

In the late 1990s it was recognized that phosphorylation of some proteins causes them to be degraded by the ATP-dependent ubiquitin/proteasome pathway. These target proteins become substrates for particular E3 ubiquitin ligases only when they are phosphorylated.

 

Oxidative phosphorylation

From Wikipedia, the free encyclopedia

Oxidative phosphorylation (or OXPHOS in short) is the metabolic pathway in which the mitochondria in cellsuse their structure, enzymes, and energy released by the oxidation of nutrients to reform ATP. Although the many forms of life on earth use a range of different nutrients, ATP is the molecule that supplies energy tometabolism. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is probably so pervasive because it is a highly efficient way of releasing energy, compared to alternative fermentationprocesses such as anaerobic glycolysis.

During oxidative phosphorylation, electrons are transferred from electron donors to electron acceptors such as oxygen, in redox reactions. These redox reactions release energy, which is used to form ATP. In eukaryotes, these redox reactions are carried out by a series of protein complexes within the cell’s intermembrane wall mitochondria, whereas, in prokaryotes, these proteins are located in the cells’ intermembrane space.

The electron transport chain in the mitochondrion is the site of oxidative phosphorylation in eukaryotes. The NADH and succinate generated in the citric acid cycle are oxidized, releasing energy to power the ATP synthase.

These linked sets of proteins are called electron transport chains. In eukaryotes, five main protein complexes are involved, whereas in prokaryotes many different enzymes are present, using a variety of electron donors and acceptors.

electron transport chain in the mitochondrion

The energy released by electrons flowing through this electron transport chain is used to transport protons across the inner mitochondrial membrane, in a process called electron transport. This generates potential energy in the form of a pH gradient and an electrical potential across this membrane. This store of energy is tapped by allowing protons to flow back across the membrane and down this gradient, through a large enzymecalled ATP synthase; this process is known as chemiosmosis. This enzyme uses this energy to generate ATP from adenosine diphosphate (ADP), in a phosphorylation reaction. This reaction is driven by the proton flow, which forces the rotation of a part of the enzyme; the ATP synthase is a rotary mechanical motor.

Although oxidative phosphorylation is a vital part of metabolism, it produces reactive oxygen species such assuperoxide and hydrogen peroxide, which lead to propagation of free radicals, damaging cells and contributing to disease and, possibly, aging (senescence). The enzymes carrying out this metabolic pathway are also the target of many drugs and poisons that inhibit their activities.

Additional References in Leaders in Pharmaceutical Intelligence

Proteomics and Biomarker Discovery

http://pharmaceuticalintelligence.com/2012/08/21/proteomics-and-biomarker-discovery/

Developments in the Genomics and Proteomics of Type 2 Diabetes Mellitus and Treatment Targets

http://pharmaceuticalintelligence.com/2013/12/08/developments-in-the-genomics-and-proteomics-of-type-2-diabetes-mellitus-and-treatment-targets/

Immune activation, immunity, antibacterial activity

http://pharmaceuticalintelligence.com/2014/07/06/immune-activation-immunity-antibacterial-activity/

Ubiquitin-Proteosome pathway, Autophagy, the Mitochondrion, Proteolysis and Cell Apoptosis: Part III

http://pharmaceuticalintelligence.com/2013/02/14/ubiquinin-proteosome-pathway-autophagy-the-mitochondrion-proteolysis-and-cell-apoptosis-reconsidered/

Ubiquinin-Proteosome pathway, autophagy, the mitochondrion, proteolysis and cell apoptosis

http://pharmaceuticalintelligence.com/2012/10/30/ubiquinin-proteosome-pathway-autophagy-the-mitochondrion-proteolysis-and-cell-apoptosis/

Research on inflammasomes opens therapeutic ways for treatment of rheumatoid arthritis

http://pharmaceuticalintelligence.com/2014/07/12/research-on-inflammasomes-opens-therapeutic-ways-for-treatment-of-rheumatoid-arthritis/

Update on mitochondrial function, respiration, and associated disorders

http://pharmaceuticalintelligence.com/2014/07/08/update-on-mitochondrial-function-respiration-and-associated-disorders/

Insert – on ETC

Overview of energy transfer by chemiosmosis[edit]

Further information: Chemiosmosis and Bioenergetics

Oxidative phosphorylation works by using energy-releasing chemical reactions to drive energy-requiring reactions: The two sets of reactions are said to be coupled. This means one cannot occur without the other. The flow of electrons through the electron transport chain, from electron donors such as NADH to electron acceptors such as oxygen, is anexergonic process – it releases energy, whereas the synthesis of ATP is an endergonic process, which requires an input of energy. Both the electron transport chain and the ATP synthase are embedded in a membrane, and energy is transferred from electron transport chain to the ATP synthase by movements of protons across this membrane, in a process called chemiosmosis.[1] In practice, this is like a simple electric circuit, with a current of protons being driven from the negative N-side of the membrane to the positive P-side by the proton-pumping enzymes of the electron transport chain. These enzymes are like a battery, as they perform work to drive current through the circuit. The movement of protons creates an electrochemical gradient across the membrane, which is often called the proton-motive force. It has two components: a difference in proton concentration (a H+gradient, ΔpH) and a difference in electric potential, with the N-side having a negative charge.[2]

ATP synthase releases this stored energy by completing the circuit and allowing protons to flow down the electrochemical gradient, back to the N-side of the membrane.[3] This kinetic energy drives the rotation of part of the enzymes structure and couples this motion to the synthesis of ATP.

The two components of the proton-motive force are thermodynamically equivalent: In mitochondria, the largest part of energy is provided by the potential; in alkaliphile bacteria the electrical energy even has to compensate for a counteracting inverse pH difference. Inversely, chloroplasts operate mainly on ΔpH. However, they also require a small membrane potential for the kinetics of ATP synthesis. At least in the case of the fusobacterium P. modestum it drives the counter-rotation of subunits a and c of the FO motor of ATP synthase.[2]

The amount of energy released by oxidative phosphorylation is high, compared with the amount produced by anaerobic fermentationGlycolysis produces only 2 ATP molecules, but somewhere between 30 and 36 ATPs are produced by the oxidative phosphorylation of the 10 NADH and 2 succinate molecules made by converting one molecule of glucoseto carbon dioxide and water,[4] while each cycle of beta oxidation of a fatty acid yields about 14 ATPs. These ATP yields are theoretical maximum values; in practice, some protons leak across the membrane, lowering the yield of ATP.[5]

Electron and proton transfer molecules[edit]

Further information: Coenzyme and Cofactor

The electron transport chain carries both protons and electrons, passing electrons from donors to acceptors, and transporting protons across a membrane. These processes use both soluble and protein-bound transfer molecules. In mitochondria, electrons are transferred within the intermembrane space by the water-soluble electron transfer protein cytochrome c.[6] This carries only electrons, and these are transferred by the reduction and oxidation of an iron atom that the protein holds within a heme group in its structure. Cytochrome c is also found in some bacteria, where it is located within the periplasmic space.[7]

Krebs_Cycler_1402785124Overview of The Electron Transport Chain

 

 

 

 

 

Reduction of coenzyme Q from itsubiquinone form (Q) to the reduced ubiquinol form (QH2).

 

Within the inner mitochondrial membrane, the lipid-soluble electron carrier coenzyme Q10 (Q) carries both electrons and protons by a redox cycle.[8] This small benzoquinone molecule is very hydrophobic, so it diffuses freely within the membrane. When Q accepts two electrons and two protons, it becomes reduced to the ubiquinol form (QH2); when QH2 releases two electrons and two protons, it becomes oxidized back to the ubiquinone (Q) form. As a result, if two enzymes are arranged so that Q is reduced on one side of the membrane and QH2 oxidized on the other, ubiquinone will couple these reactions and shuttle protons across the membrane.[9] Some bacterial electron transport chains use different quinones, such as menaquinone, in addition to ubiquinone.[10]

Within proteins, electrons are transferred between flavin cofactors,[3][11] iron–sulfur clusters, and cytochromes. There are several types of iron–sulfur cluster. The simplest kind found in the electron transfer chain consists of two iron atoms joined by two atoms of inorganic sulfur; these are called [2Fe–2S] clusters. The second kind, called [4Fe–4S], contains a cube of four iron atoms and four sulfur atoms. Each iron atom in these clusters is coordinated by an additional amino acid, usually by the sulfur atom of cysteine. Metal ion cofactors undergo redox reactions without binding or releasing protons, so in the electron transport chain they serve solely to transport electrons through proteins. Electrons move quite long distances through proteins by hopping along chains of these cofactors.[12] This occurs by quantum tunnelling, which is rapid over distances of less than 1.4×10−9 m.[13]

Eukaryotic electron transport chains[edit]

Further information: Electron transport chain and Chemiosmosis

Many catabolic biochemical processes, such as glycolysis, the citric acid cycle, and beta oxidation, produce the reduced coenzyme NADH. This coenzyme contains electrons that have a high transfer potential; in other words, they will release a large amount of energy upon oxidation. However, the cell does not release this energy all at once, as this would be an uncontrollable reaction. Instead, the electrons are removed from NADH and passed to oxygen through a series of enzymes that each release a small amount of the energy. This set of enzymes, consisting of complexes I through IV, is called the electron transport chain and is found in the inner membrane of the mitochondrion. Succinate is also oxidized by the electron transport chain, but feeds into the pathway at a different point.

In eukaryotes, the enzymes in this electron transport system use the energy released from the oxidation of NADH to pump protons across the inner membrane of the mitochondrion. This causes protons to build up in the intermembrane space, and generates an electrochemical gradient across the membrane. The energy stored in this potential is then used by ATP synthase to produce ATP. Oxidative phosphorylation in the eukaryotic mitochondrion is the best-understood example of this process. The mitochondrion is present in almost all eukaryotes, with the exception of anaerobic protozoa such as Trichomonas vaginalis that instead reduce protons to hydrogen in a remnant mitochondrion called a hydrogenosome.[14]

 

Typical respiratory enzymes and substrates in eukaryotes.
Respiratory enzyme Redox pair Midpoint potential (Volts)
NADH dehydrogenase NAD+ / NADH −0.32[15]
Succinate dehydrogenase FMN or FAD / FMNH2 or FADH2 −0.20[15]
Cytochrome bc1 complex Coenzyme Q10ox / Coenzyme Q10red +0.06[15]
Cytochrome bc1 complex Cytochrome box / Cytochrome bred +0.12[15]
Complex IV Cytochrome cox / Cytochrome cred +0.22[15]
Complex IV Cytochrome aox / Cytochrome ared +0.29[15]
Complex IV O2 / HO +0.82[15]
Conditions: pH = 7[15]

 

NADH-coenzyme Q oxidoreductase (complex I)[edit]

NADH-coenzyme Q oxidoreductase, also known as NADH dehydrogenase or complex I, is the first protein in the electron transport chain.[16] Complex I is a giant enzyme with the mammalian complex I having 46 subunits and a molecular mass of about 1,000 kilodaltons (kDa).[17] The structure is known in detail only from a bacterium;[18][19]  in most organisms the complex resembles a boot with a large “ball” poking out from the membrane into the mitochondrion.[20][21]

Complex I or NADH-Q oxidoreductase

 

 

Complex I or NADH-Q oxidoreductase. The abbreviations are discussed in the text. In all diagrams of respiratory complexes in this article, the matrix is at the bottom, with the intermembrane space above.

The genes that encode the individual proteins are contained in both the cell nucleus and themitochondrial genome, as is the case for many enzymes present in the mitochondrion.

The reaction that is catalyzed by this enzyme is the two electron oxidation of NADH by coenzyme Q10 or ubiquinone(represented as Q in the equation below), a lipid-soluble quinone that is found in the mitochondrion membrane:

The start of the reaction, and indeed of the entire electron chain, is the binding of a NADH molecule to complex I and the donation of two electrons. The electrons enter complex I via a prosthetic group attached to the complex, flavin mononucleotide (FMN). The addition of electrons to FMN converts it to its reduced form, FMNH2. The electrons are then transferred through a series of iron–sulfur clusters: the second kind of prosthetic group present in the complex.[18] There are both [2Fe–2S] and [4Fe–4S] iron–sulfur clusters in complex I.

As the electrons pass through this complex, four protons are pumped from the matrix into the intermembrane space. Exactly how this occurs is unclear, but it seems to involve conformational changes in complex I that cause the protein to bind protons on the N-side of the membrane and release them on the P-side of the membrane.[22] Finally, the electrons are transferred from the chain of iron–sulfur clusters to a ubiquinone molecule in the membrane.[16] Reduction of ubiquinone also contributes to the generation of a proton gradient, as two protons are taken up from the matrix as it is reduced to ubiquinol (QH2).

Succinate-Q oxidoreductase (complex II)[edit]

Succinate-Q oxidoreductase, also known as complex II or succinate dehydrogenase, is a second entry point to the electron transport chain.[23] It is unusual because it is the only enzyme that is part of both the citric acid cycle and the electron transport chain. Complex II consists of four protein subunits and contains a bound flavin adenine dinucleotide (FAD) cofactor, iron–sulfur clusters, and a hemegroup that does not participate in electron transfer to coenzyme Q, but is believed to be important in decreasing production of reactive oxygen species.[24][25]

Complex II

 

 

Complex II: Succinate-Q oxidoreductase.

It oxidizes succinate to fumarate and reduces ubiquinone.As this reaction releases less energy than the oxidation of NADH, complex II does not transport protons across the membrane and does not contribute to the proton gradient.

In some eukaryotes, such as the parasitic worm Ascaris suum, an enzyme similar to complex II, fumarate reductase (menaquinol:fumarate oxidoreductase, or QFR), operates in reverse to oxidize ubiquinol and reduce fumarate. This allows the worm to survive in the anaerobic environment of the large intestine, carrying out anaerobic oxidative phosphorylation with fumarate as the electron acceptor.[26] Another unconventional function of complex II is seen in the malaria parasite Plasmodium falciparum. Here, the reversed action of complex II as an oxidase is important in regenerating ubiquinol, which the parasite uses in an unusual form ofpyrimidine biosynthesis.[27]

Electron transfer flavoprotein-Q oxidoreductase[edit]

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-Q oxidoreductase), also known as electron transferring-flavoprotein dehydrogenase, is a third entry point to the electron transport chain. It is an enzyme that accepts electrons from electron-transferring flavoprotein in the mitochondrial matrix, and uses these electrons to reduce ubiquinone.[28] This enzyme contains a flavin and a [4Fe–4S] cluster, but, unlike the other respiratory complexes, it attaches to the surface of the membrane and does not cross the lipid bilayer.[29]

In mammals, this metabolic pathway is important in beta oxidation of fatty acids and catabolism of amino acids and choline, as it accepts electrons from multiple acetyl-CoAdehydrogenases.[30][31] In plants, ETF-Q oxidoreductase is also important in the metabolic responses that allow survival in extended periods of darkness.[32]

 

Q-cytochrome c oxidoreductase (complex III)[edit]

Q-cytochrome c oxidoreductase is also known as cytochrome c reductasecytochrome bc1 complex, or simply complex III.[33][34] In mammals, this enzyme is a dimer, with each subunit complex containing 11 protein subunits, an [2Fe-2S] iron–sulfur cluster and three cytochromes: one cytochrome c1 and two bcytochromes.[35] A cytochrome is a kind of electron-transferring protein that contains at least one hemegroup. The iron atoms inside complex III’s heme groups alternate between a reduced ferrous (+2) and oxidized ferric (+3) state as the electrons are transferred through the protein.

complex III

 

 

The two electron transfer steps in complex III: Q-cytochrome c oxidoreductase. After each step, Q (in the upper part of the figure) leaves the enzyme.

The reaction catalyzed by complex III is the oxidation of one molecule of ubiquinol and the reduction of two molecules of cytochrome c, a heme protein loosely associated with the mitochondrion. Unlike coenzyme Q, which carries two electrons, cytochrome c carries only one electron.

As only one of the electrons can be transferred from the QH2 donor to a cytochrome c acceptor at a time, the reaction mechanism of complex III is more elaborate than those of the other respiratory complexes, and occurs in two steps called the Q cycle.[36] In the first step, the enzyme binds three substrates, first, QH2, which is then oxidized, with one electron being passed to the second substrate, cytochrome c. The two protons released from QH2 pass into the intermembrane space. The third substrate is Q, which accepts the second electron from the QH2 and is reduced to Q.-, which is the ubisemiquinone free radical. The first two substrates are released, but this ubisemiquinone intermediate remains bound. In the second step, a second molecule of QH2 is bound and again passes its first electron to a cytochrome c acceptor. The second electron is passed to the bound ubisemiquinone, reducing it to QH2 as it gains two protons from the mitochondrial matrix. This QH2 is then released from the enzyme.[37]

As coenzyme Q is reduced to ubiquinol on the inner side of the membrane and oxidized to ubiquinone on the other, a net transfer of protons across the membrane occurs, adding to the proton gradient.[3] The rather complex two-step mechanism by which this occurs is important, as it increases the efficiency of proton transfer. If, instead of the Q cycle, one molecule of QH2 were used to directly reduce two molecules of cytochrome c, the efficiency would be halved, with only one proton transferred per cytochrome c reduced.[3]

 

Cytochrome c oxidase (complex IV)[edit]

For more details on this topic, see cytochrome c oxidase.

Cytochrome c oxidase, also known as complex IV, is the final protein complex in the electron transport chain.[38] The mammalian enzyme has an extremely complicated structure and contains 13 subunits, two heme groups, as well as multiple metal ion cofactors – in all, three atoms of copper, one of magnesium and one of zinc.[39]

This enzyme mediates the final reaction in the electron transport chain and transfers electrons to oxygen, while pumping protons across the membrane.[40] The final electron acceptor oxygen, which is also called the terminal electron acceptor, is reduced to water in this step. Both the direct pumping of protons and the consumption of matrix protons in the reduction of oxygen contribute to the proton gradient. The reaction catalyzed is the oxidation of cytochrome c and the reduction of oxygen:

Complex IV

 

 

Complex IV: cytochrome c oxidase.

Organization of complexes[edit]

The original model for how the respiratory chain complexes are organized was that they diffuse freely and independently in the mitochondrial membrane.[17] However, recent data suggest that the complexes might form higher-order structures called supercomplexes or “respirasomes.”[49] In this model, the various complexes exist as organized sets of interacting enzymes.[50] These associations might allow channeling of substrates between the various enzyme complexes, increasing the rate and efficiency of electron transfer.[51] Within such mammalian supercomplexes, some components would be present in higher amounts than others, with some data suggesting a ratio between complexes I/II/III/IV and the ATP synthase of approximately 1:1:3:7:4.[52] However, the debate over this supercomplex hypothesis is not completely resolved, as some data do not appear to fit with this model.[17][53]

 

Reversible protein phosphorylation, principally on serine, threonine or tyrosine residues, is one of the most important and well-studied post-translational modifications. Phosphorylation plays critical roles in the regulation of many cellular processes including cell cycle, growth, apoptosis and signal transduction pathways.

Phosphorylation is the most common mechanism of regulating protein function and transmitting signals throughout the cell. While phosphorylation has been observed in bacterial proteins, it is considerably more pervasive in eukaryotic cells. It is estimated that one-third of the proteins in the human proteome are substrates for phosphorylation at some point (1). Indeed, phosphoproteomics has been established as a branch of proteomics that focuses solely on the identification and characterization of phosphorylated proteins.

Mechanism of Phosphorylation
While phosphorylation is a prevalent post-translational modification (PTM) for regulating protein function, it only occurs at the side chains of three amino acids, serine, threonine and tyrosine, in eukaryotic cells. These amino acids have a nucleophilic (–OH) group that attacks the terminal phosphate group (γ-PO32-) on the universal phosphoryl donor adenosine triphosphate (ATP), resulting in the transfer of the phosphate group to the amino acid side chain. This transfer is facilitated by magnesium (Mg2+), which chelates the γ- and β-phosphate groups to lower the threshold for phosphoryl transfer to the nucleophilic (–OH) group. This reaction is unidirectional because of the large amount of free energy that is released when the phosphate-phosphate bond in ATP is broken to form adenosine diphosphate (ADP).

Serine Phosphorylation

 

 

 

http://www.piercenet.com/media/Serine%20Phosphorylation.jpg

Diagram of serine phosphorylation. Enzyme-catalyzed proton transfer from the (–OH) group on serine stimulates the nucleophilic attack of the γ-phosphate group on ATP, resulting in transfer of the phosphate group to serine to form phosphoserine and ADP. (—B:) indicates the enzyme base that initiates proton transfer.

For a large subset of proteins, phosphorylation is tightly associated with protein activity and is a key point of protein function regulation. Phosphorylation regulates protein function and cell signaling by causing conformational changes in the phosphorylated protein. These changes can affect the protein in two ways. First, conformational changes regulate the catalytic activity of the protein. Thus, a protein can be either activated or inactivated by phosphorylation. Second, phosphorylated proteins recruit neighboring proteins that have structurally conserved domains that recognize and bind to phosphomotifs. These domains show specificity for distinct amino acids. For example, Src homology 2 (SH2) and phosphotyrosine binding (PTB) domains show specificity for phosphotyrosine (pY), although distinctions in these two structures give each domain specificity for distinct phosphotyrosine motifs (2). Phosphoserine (pS) recognition domains include MH2 and the WW domain, while phosphothreonine (pT) is recognized by forkhead-associated (FHA) domains. The ability of phosphoproteins to recruit other proteins is critical for signal transduction, in which downstream effector proteins are recruited to phosphorylated signaling proteins.

Protein phosphorylation is a reversible PTM that is mediated by kinases and phosphatases, which phosphorylate and dephosphorylate substrates, respectively. These two families of enzymes facilitate the dynamic nature of phosphorylated proteins in a cell. Indeed, the size of the phosphoproteome in a given cell is dependent upon the temporal and spatial balance of kinase and phosphatase concentrations in the cell and the catalytic efficiency of a particular phosphorylation site.

Phosphorylation is a reversible PTM that regulates protein function

 

 

 

http://www.piercenet.com/media/Phosphorylation%20Dephosphorylation.jpg

Phosphorylation is a reversible PTM that regulates protein function. Left panel: Protein kinases mediate phosphorylation at serine, threonine and tyrosine side chains, and phosphatases reverse protein phosphorylation by hydrolyzing the phosphate group. Right panel: Phosphorylation causes conformational changes in proteins that either activate (top) or inactivate (bottom) protein function.

Protein Kinases
Kinases are enzymes that facilitate phosphate group transfer to substrates. Greater than 500 kinases have been predicted in the human proteome; this subset of proteins comprises the human kinome (3). Substrates for kinase activity are diverse and include lipids, carbohydrates, nucleotides and proteins.ATP is the cosubstrate for almost all protein kinases, although guanosine triphosphate is used by a small number of kinases. ATP is the ideal structure for the transfer of α-, β- or γ-phosphate groups for nucleotidyl-, pyrophosphoryl- or phosphoryltransfer, respectively (4). While the substrate specificity of kinases varies, the ATP-binding site is generally conserved (5).Protein kinases are categorized into subfamilies that show specificity for distinct catalytic domains and include tyrosine kinases or serine/threonine kinases. Approximately 80% of the mammalian kinome comprises serine/threonine kinases, and >90% of the phosphoproteome consists of pS and pT. Indeed, studies have shown that the relative abundance ratio of pS:pT:pY in a cell is 1800:200:1 (6). Although pY is not as prevalent as pS and pT, global tyrosine phosphorylation is at the forefront of biomedical research because of its relation to human disease via the dysregulation of receptor tyrosine kinases (RTKs).Protein kinase substrate specificity is based not only on the target amino acid but also on consensus sequences that flank it (7). These consensus sequences allow some kinases to phosphorylate single proteins and others to phosphorylate multiple substrates (>300) (5). Additionally, kinases can phosphorylate single or multiple amino acids on an individual protein if the kinase-specific consensus sequences are available.

Kinases have regulatory subunits that function as activating or autoinhibitory domains and have various regulatory substrates. Phosphorylation of these subunits is a common approach to regulating kinase activity (8). Most protein kinases are dephosphorylated and inactive in the basal state and are activated by phosphorylation. A small number of kinases are constitutively active and are made intrinsically inefficient, or inactive, when phosphorylated. Some kinases, such as Src, require a combination of phosphorylation and dephosphorylation to become active, indicating the high regulation of this proto-oncogene. Scaffolding and adaptor proteins can also influence kinase activity by regulating the spatial relationship between kinases and upstream regulators and downstream substrates.

Signal Transduction Cascades
The reversibility of protein phosphorylation makes this type of PTM ideal for signal transduction, which allows cells to rapidly respond to intracellular or extracellular stimuli. Signal transduction cascades are characterized by one or more proteins physically sensing cues, either through ligand binding, cleavage or some other response, that then relay the signal to second messengers and signaling enzymes. In the case of phosphorylation, these receptors activate downstream kinases, which then phosphorylate and activate their cognate downstream substrates, including additional kinases, until the specific response is achieved. Signal transduction cascades can be linear, in which kinase A activates kinase B, which activates kinase C and so forth. Signaling pathways have also been discovered that amplify the initial signal; kinase A activates multiple kinases, which in turn activate additional kinases. With this type of signaling, a single molecule, such as a growth factor, can activate global cellular programs such as proliferation (9).

 

Signal Transduction Pathways

 

 

http://www.piercenet.com/media/Signal%20Transduction%20Pathways.jpg

Signal transduction cascades amplify the signal output. External and internal stimuli induce a wide range of cellular responses through a series of second messengers and enzymes. Linear signal transduction pathways yield the sequential activation of a discrete number of downstream effectors, while other stimuli elicit signal cascades that amplify the initial stimulus for large-scale or global cellular responses.

Protein Phosphatases
The intensity and duration of phosphorylation-dependent signaling is regulated by three mechanisms (5):

  • Removal of the activating ligand
  • Kinase or substrate proteolysis
  • Phosphatase-dependent dephosphorylation

The human proteome is estimated to contain approximately 150 protein phosphatases, which show specificity for pS/pT and pY residues (10,11). While dephosphorylation is the end goal of these two groups of phosphatases, they do it through separate mechanisms. Serine/threonine phosphatases mediate the direct hydrolysis of the phosphorus atom of the phosphate group using a bimetallic (Fe/Zn) center, while tyrosine phosphatases form a covalent thiophosphoryl intermediate that facilitates removal of the tyrosine residue.

 

Phosphorylation and Ubiquitylation

Almost all aspects of biology are regulated by reversible protein phosphorylation and ubiquitylation. Abnormalities in these pathways cause numerous diseases including cancer, neurodegeneration and inflammation – all conditions under intense scrutiny in our Unit. Deciphering how disruptions in phosphorylation and ubiquitin networks lead to disease will reveal novel drug targets and improved strategies to treat these maladies in the future.

Protein ubiquitylation is analogous to protein phosphorylation except that ubiquitin molecules are attached covalently to Lys residues, as opposed to phosphate groups becoming covalently attached to one or more Ser, Thr or Tyr residues. Like phosphorylation, ubiquitylation can alter protein properties and functions in every conceivable way. Ubiquitylation is likely to be a more versatile control mechanism than phosphorylation, as ubiquitin molecules can not only be linked to one or more amino acid residues on the same protein, but can also form ubiquitin chains.

Moreover, there are also several ubiquitin-like modifiers (ULMs), such as Nedd8, SUMO1, SUMO2, SUMO3, FAT10 and ISG15, which can become attached to proteins in reactions termed Neddylation, SUMOylation, Tenylation and ISGylation, while poly-SUMO chains (involving SUMO2 and SUMO3) are also formed in cells. Recent research has highlighted an exquisite interplay between phosphorylation and ubiquitin pathways that regulate many physiological systems.

phos_deubuiq

 

 

 

http://www.ppu.mrc.ac.uk/overview/images/phos_deubuiq.jpg

Protein ubiquitylation is an even more versatile control mechanism
than protein phosphorylation

This includes pathways of relevance to understanding innate immunity, Parkinson’s disease and cancer, emphasising the importance of integrating phosphorylation and ubiquitylation research, and not considering these separate areas to be studied in isolation.

Phosphorylation Ubiquitylation
Discovered 1955 Discovered 1978
>500 protein kinases ~10 E1s, ~40 E2s
>600 E3 ligases
140 protein phosphatases ~100 deubiquitylases
Nobel Prize 1992 Nobel Prize 2004
First drug approval
2001 (Gleevec)
First drug approval
2003 (Bortezomib)
16 drugs approved,
>150 in clinical trials
15 drugs in Phase I/II
Current sales of
USS$15 billion p.a.
Current sales of
USS$1.5 billion p.a.
30% of Pharma R&D <<1% of Pharma R&D

 

History of the development of protein phoshorylation and ubiquitylation

The MRC-PPU research focuses on unravelling the roles of protein phosphorylation and ubiquitylation pathways that have strong links to understanding human disease. This is where we can make the best use of our expertise, grasp opportunities emerging from the golden era of genetic analysis of human disease, and make a significant contribution to medical research.

Our Principal Investigators (PIs) deploy a blend of creativity, curiosity, expertise and state-of-the-art technology to tackle their selected projects. Their aim is to uncover fundamentally new knowledge on how biological systems are controlled, hopefully shedding novel insights into the understanding and treatment of disease. Effective translation of our research will also be impossible without robust interactions with drug discovery units such as the MRC Technology Centre for Therapeutics Discovery, the University of Dundee’s Drug Discovery Unit and close collaboration with pharmaceutical companies.

The latter will be greatly enhanced by major collaborations with the six pharmaceutical companies that support the Division of Signal Transduction Therapy. Access to the exceptional support services available within the MRC-PPU and DSTT also helps to maximise the competitiveness of our research groups and reinforce collaborations with our external partners.

Central questions being addressed by our PIs include understanding how ubiquitin and phosphorylation pathways are organised, characterising the interplay between these pathways, determining how they recognise and respond to signals, and uncovering how disruption of these networks causes disease. The expectation is that the data, reagents and expertise emerging from our research and working effectively with clinicians and pharmaceutical industry will enable us to devise new

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3:45 – 4:15, 2014, Scott Lowe “Tumor suppressor and tumor maintenance genes”

12:00 – 12:30, 6/13/2014, John Maraganore “Progress in advancement of RNAi therapeutics”

9:30 – 10:00, 6/13/2014, David Bartel “MicroRNAs, poly(A) tails and post-transcriptional gene regulation.”

10:00 – 10:30, 6/13/2014, Joshua Mendell “Novel microRNA functions in mammalian physiology and cancer”

Aviva Lev-Ari, PhD, RN

http://pharmaceuticalintelligence.com/2014/06/04/koch-institute-for-integrative-cancer-research-mit-summer-symposium-2014-rna-biology-cancer-and-therapeutic-implications-june-13-2014-830am-430pm-kresge-auditorium-mit/

Targeted genome editing by lentiviral protein transduction of zinc-finger and TAL-effector nucleases          Aviva Lev-Ari, PhD, RN

http://pharmaceuticalintelligence.com/2014/06/04/targeted-genome-editing-by-lentiviral-protein-transduction-of-zinc-finger-and-tal-effector-nucleases/

Illana Gozes discovered Novel Protein Fragments that have proven Protective Properties for Cognitive Functioning

Aviva Lev-Ari, PhD, RN

http://pharmaceuticalintelligence.com/2014/06/03/prof-illana-gozes-discovered-novel-protein-fragments-that-have-proven-protective-properties-for-cognitive-functioning/

 

 

 

 

 

 

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Larry H. Benstein, MD, FCAP, Gurator and writer

http://pharmaceuticalintelligence.com/7/8/2014/Update on mitochondrial function, respiration, and associated disorders

This is a condensed account of very recent published work on respiration and disturbed mitochondrail function.  We know that their is an equilibrium between respiration and autophagy in eukaryotic cells.  The Krebs Cycle produces 32 ATPs in oxidative phosphorylation, which is far more efficient than glycolysis.  There is also a different contribution of mitochondrial metabolism, in the balance, between tissues that are synthetic and those that are catabolic.  This is a subject long understood, essential for cellular energetics, and not adequately explored.

 

Gain-of-Function Mutant p53 Promotes Cell Growth and Cancer Cell Metabolism via Inhibition of AMPK Activation.

Zhou G1Wang J2Zhao M2Xie TX2Tanaka N2, et al.
Mol Cell. 
2014 Jun 19;54(6):960-974.   doi: 10.1016/j.molcel.2014.04.024. 

Many mutant p53 proteins (mutp53s) exert oncogenic gain-of-function (GOF) properties, but the mechanisms mediating these functions remain poorly defined.

We show here that GOF mutp53s inhibit AMP-activated protein kinase (AMPK) signaling in head and neck cancer cells.

Conversely, downregulation of GOF mutp53s enhances AMPK activation under energy stress, decreasing the activity of the anabolic factors acetyl-CoA carboxylase and ribosomal protein S6 and inhibiting aerobic glycolytic potential and invasive cell growth.

Under conditions of energy stress, GOF mutp53s, but not wild-type p53, preferentially bind to the AMPKα subunit and inhibit AMPK activation.

Given the importance of AMPK as an energy sensor and tumor suppressor that inhibits anabolic metabolism, our findings reveal that direct inhibition of AMPK activation is an important mechanism through which mutp53s can gain oncogenic function. PMID:24857548

Investigating and Targeting Chronic Lymphocytic Leukemia Metabolism with the HIV Protease Inhibitor Ritonavir and Metformin.

Adekola KUAydemir SDMa SZhou ZRosen STShanmugam M.
Leuk Lymphoma. 2014 May 14:1-23.

Chronic Lymphocytic Leukemia (CLL) remains fatal due to the development of resistance to existing therapies. Targeting abnormal glucose metabolism sensitizes various cancer cells to chemotherapy and/or elicits toxicity.

Examination of glucose dependency in CLL demonstrated variable sensitivity to glucose deprivation. Further evaluation of metabolic dependencies of CLL cells resistant to glucose deprivation revealed increased engagement of fatty acid oxidation upon glucose withdrawal.

Investigation of glucose transporter expression in CLL reveals up-regulation of glucose transporter GLUT4. Treatment of CLL cells with HIV protease inhibitor ritonavir, that inhibits GLUT4, elicits toxicity similar to that elicited upon glucose-deprivation.

CLL cells resistant to ritonavir are sensitized by co-treatment with metformin, potentially targeting compensatory mitochondrial complex 1 activity. Ritonavir and metformin have been administered in humans for treatment of diabetes in HIV patients, demonstrating the tolerance of this combination in humans. Our studies strongly substantiate further investigation of FDA approved ritonavir and metformin for CLL.

KEYWORDS:  Basic Biology; Chemotherapeutic approaches; Lymphoid Leukemia; Signal transduction             PMID: 24828872

Utilizing hydrogen sulfide as a novel anti-cancer agent by targeting cancer glycolysis and pH imbalance.

Lee ZW1Teo XYTay EYTan CHHagen TMoore PKDeng LW.
Br J Pharmacol. 2014 May 15.    doi: 10.1111/bph.12773

Many disparate studies have reported the ambiguous role of hydrogen sulfide (H2 S) in cell survival. The present study investigated the effect of H2 S on viability of cancer and non-cancer cells.

Cancer and non-cancer cells were exposed to H2 S (using sodium hydrosulfide, NaHS and GYY4137) and cell viability was examined by crystal violet assay. We then examined cancer cellular glycolysis process by in vitro enzymatic assays and pH regulator activity. Lastly, intracellular pH (pHi) was determined by ratiometric pHi measurement using BCECF staining.

Continuous, but not single, exposure to H2 S decreased cell survival more effectively in cancer cells, as compared to non-cancer cells. Slow H2 S-releasing donor, GYY4137, significantly increased glycolysis leading to overproduction of lactate. H2 S also decreased anion exchanger and sodium/proton exchanger activity. The combination of increased metabolic acid production and defective pH regulation resulted in an uncontrolled intracellular acidification leading to cancer cell death. In contrast, no significant intracellular acidification or cell death was observed in non-cancer cells.

Low and continuous exposure to H2 S targets metabolic processes and pH homeostasis in cancer cells, potentially serving as a novel and selective anti-cancer strategy.

KEYWORDS:  cancer cell death; cancer glucose metabolism; hydrogen sulfide; pH homeostasis          PMID: 24827113


Agonism of the 5-Hydroxytryptamine 1F Receptor Promotes Mitochondrial Biogenesis and Recovery from Acute Kidney Injury

Garrett SMWhitaker RMBeeson CC, and Schnellmann RG

Center for Cell Death, Injury, and Regeneration, Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, South Carolina (S.M.G., R.M.W., C.C.B., R.G.S.); and Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina (R.G.S.)
Address correspondence to: Dr. Rick G. Schnellmann, Department of Drug Discovery and Biomedical Sciences, MUSC, Charleston, SC 29425.
E-mail: schnell@musc.edu

Many acute and chronic conditions, such as acute kidney injury, chronic kidney disease, heart failure, and liver disease, involve mitochondrial dysfunction. Although we have provided evidence that drug-induced stimulation of mitochondrial biogenesis (MB) accelerates mitochondrial and cellular repair, leading to recovery of organ function, only a limited number of chemicals have been identified that induce MB.

The goal of this study was to assess the role of the 5-hydroxytryptamine 1F (5-HT1F) receptor in MB. Immunoblot and quantitative polymerase chain reaction analyses revealed 5-HT1F receptor expression in renal proximal tubule cells (RPTC). A MB screening assay demonstrated that two selective 5-HT1F receptor agonists,

  1. LY334370 (4-fluoro-N-[3-(1-methyl-4-piperidinyl)-1H-indol-5-yl]benzamide) and
  2. LY344864 (N-[(3R)-3-(dimethylamino)-2,3,4,9-tetrahydro-1H-carbazol-6-yl]-4-fluorobenzamide; 1–100 nM)

increased carbonylcyanide-p-trifluoromethoxyphenylhydrazone–uncoupled oxygen consumption in RPTC, and

  • validation studies confirmed both agonists increased mitochondrial proteins  in vitro.
    [e.g., ATP synthase β, cytochrome c oxidase 1 (Cox1), and NADH dehydrogenase (ubiquinone) 1β subcomplex subunit 8 (NDUFB8)]

Small interfering RNA knockdown of the 5-HT1F receptor

  • blocked agonist-induced MB.

Furthermore, LY344864 increased

  • peroxisome proliferator–activated receptor (PPAR) coactivator 1-α, Cox1, and
  • NDUFB8 transcript levels and
  • mitochondrial DNA (mtDNA) copy number

in murine renal cortex, heart, and liver.

Finally, LY344864 accelerated recovery of renal function, as indicated by

  • decreased blood urea nitrogen and kidney injury molecule 1 and
  • increased mtDNA copy number

following ischemia/reperfusion-induced acute kidney injury (AKI).

In summary, these studies reveal that

  • the 5-HT1F receptor is linked to MB, 5-HT1F receptor agonism promotes MB in vitro and in vivo, and

5-HT1F receptor agonism promotes recovery from AKI injury.

Induction of MB through 5-HT1F receptor agonism represents a new target and approach to treat mitochondrial organ dysfunction.

Footnotes

  • Portions of this work have been presented previously: Garrett SM, Wills LP, and Schnellmann RG (2012) Serotonin (5-HT) 1F receptor agonism as a potential treatment for acceleration of recovery from acute kidney injury.American Society of Nephrology Annual Meeting; 2012 Nov 1–4; San Diego, CA.
  • dx.doi.org/10.1124/jpet.114.214700.

Ca2+ regulation of mitochondrial function in neurons.

Rueda CB1Llorente-Folch I1Amigo I1Contreras L1González-Sánchez P1Martínez-Valero P1Juaristi I1Pardo B1Del Arco A2Satrústegui J3

Biochim Biophys Acta. 2014 May 10. pii: S0005-2728(14)00126-1.
doi: 10.1016/j.bbabio.2014.04.010.

Calcium is thought to regulate respiration but it is unclear whether this is dependent on the increase in ATP demand caused by any Ca2+ signal or to Ca2+ itself.

[Na+]i, [Ca2+]i and [ATP]i dynamics in intact neurons exposed to different workloads in the absence and presence of Ca2+ clearly showed that

  • Ca2+-stimulation of coupled respiration is required to maintain [ATP]i levels.

Ca2+ may regulate respiration by

  1. activating metabolite transport in mitochondria from outer face of the inner mitochondrial membrane, or
  2. after Ca2+ entry in mitochondria through the calcium uniporter (MCU).

Two Ca2+-regulated mitochondrial metabolite transporters are expressed in neurons,

  1. the aspartate-glutamate exchanger ARALAR/AGC1/Slc25a12, a component of the malate-aspartate shuttle, with a Kd for Ca2+ activation of 300nM, and
  2. the ATP-Mg/Pi exchanger SCaMC-3/Slc25a23, with S0.5 for Ca2+ of 300nM and 3.4μM, respectively.

The lack of SCaMC-3 results in a smaller Ca2+-dependent stimulation of respiration only at high workloads, as caused by veratridine, whereas

  • the lack of ARALAR reduced by 46% basal OCR in intact neurons using glucose as energy source and the Ca2+-dependent responses to all workloads (veratridine, K+-depolarization, carbachol).

The lack of ARALAR caused a reduction of about 65-70% in the response to the high workload imposed by veratridine, and

  • completely suppressed the OCR responses to moderate (K+-depolarization) and small (carbachol) workloads,
  • effects reverted by pyruvate supply.

For K+-depolarization, this occurs in spite of the presence of large [Ca2+]mit signals and increased reduction of mitochondrial NAD(P)H.

These results show that ARALAR-MAS is a major contributor of Ca2+-stimulated respiration in neurons

  • by providing increased pyruvate supply to mitochondria.

In its absence and under moderate workloads, matrix Ca2+ is unable to stimulate pyruvate metabolism and entry in mitochondria suggesting a limited role of MCU in these conditions.

This article was invited for a Special Issue entitled: 18th European Bioenergetic Conference.    Copyright © 2014. Published by Elsevier B.V.

KEYWORDS:  ATP-Mg/Pi transporter; Aspartate–glutamate transporter; Calcium; Calcium-regulated transport; Mitochondrion; Neuronal respiration PMID: 24820519

 

Sestrin2 inhibits uncoupling protein 1 expression through suppressing reactive oxygen species.

Ro SH1Nam M2Jang I1Park HW1Park H1Semple IA1Kim M1et al.
Proc Natl Acad Sci U S A. 2014 May 27;111(21):7849-54.
doi: 10.1073/pnas.1401787111.

Uncoupling protein 1 (Ucp1), which is localized in the mitochondrial inner membrane of mammalian brown adipose tissue (BAT), generates heat by uncoupling oxidative phosphorylation. Upon cold exposure or nutritional abundance, sympathetic neurons stimulate BAT to express Ucp1 to induce energy dissipation and thermogenesis. Accordingly, increased Ucp1 expression reduces obesity in mice and is correlated with leanness in humans.

Despite this significance, there is currently a limited understanding of how Ucp1 expression is physiologically regulated at the molecular level. Here, we describe the involvement of Sestrin2 and reactive oxygen species (ROS) in regulation of Ucp1 expression. Transgenic overexpression of Sestrin2 in adipose tissues inhibited both basal and cold-induced Ucp1 expression in interscapular BAT, culminating in decreased thermogenesis and increased fat accumulation.

Endogenous Sestrin2 is also important for suppressing Ucp1 expression because BAT from Sestrin2(-/-) mice exhibited a highly elevated level of Ucp1 expression. The redox-inactive mutant of Sestrin2 was incapable of regulating Ucp1 expression, suggesting that Sestrin2 inhibits Ucp1 expression primarily through reducing ROS accumulation.

Consistently, ROS-suppressing antioxidant chemicals, such as butylated hydroxyanisole and N-acetylcysteine, inhibited cold- or cAMP-induced Ucp1 expression as well. p38 MAPK, a signaling mediator required for cAMP-induced Ucp1 expression, was inhibited by either Sestrin2 overexpression or antioxidant treatments.

Taken together, these results suggest that Sestrin2 and antioxidants inhibit Ucp1 expression through suppressing ROS-mediated p38 MAPK activation, implying a critical role of ROS in proper BAT metabolism.

KEYWORDS: aging; homeostasis; mouse; β-adrenergic signaling      PMID: 24825887     PMCID:  PMC4040599

Mitochondrial EF4 links respiratory dysfunction and cytoplasmic translation in Caenorhabditis elegans.

Yang F1Gao Y1Li Z2Chen L3Xia Z4Xu T5Qin Y6
Biochim Biophys Acta. 2014 May 15. pii: S0005-2728(14)00499-X.
doi: 10.1016/j.bbabio.2014.05.353.

How animals coordinate cellular bioenergetics in response to stress conditions is an essential question related to aging, obesity and cancer. Elongation factor 4 (EF4/LEPA) is a highly conserved protein that promotes protein synthesis under stress conditions, whereas its function in metazoans remains unknown.

Here, we show that, in Caenorhabditis elegans, the mitochondria-localized CeEF4 (referred to as mtEF4) affects mitochondrial functions, especially at low temperature (15°C).

At worms’ optimum growing temperature (20°C), mtef4 deletion leads to self-brood size reduction, growth delay and mitochondrial dysfunction.

Transcriptomic analyses show that mtef4 deletion induces retrograde pathways, including mitochondrial biogenesis and cytoplasmic translation reorganization.

At low temperature (15°C), mtef4 deletion reduces mitochondrial translation and disrupts the assembly of respiratory chain supercomplexes containing complex IV.

These observations are indicative of the important roles of mtEF4 in mitochondrial functions and adaptation to stressful conditions.

Copyright © 2014. Published by Elsevier B.V.

KEYWORDSC. elegans; EF4(LepA/GUF1); Mitochondrial dysfunction; Retrograde pathways; Translation    PMID:  24837196

The metabolite α-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR.

Chin RM1Fu X2Pai MY3Vergnes L4Hwang H5Deng G6Diep S2, et al.
Nature  2014 Jun 19;509(7505):397-401. doi: 10.1038/nature13264. 

Metabolism and ageing are intimately linked. Compared with ad libitum feeding, dietary restriction consistently extends lifespan and delays age-related diseases in evolutionarily diverse organisms. Similar conditions of nutrient limitation and genetic or pharmacological perturbations of nutrient or energy metabolism also have longevity benefits.

Recently, several metabolites have been identified that modulate ageing; however, the molecular mechanisms underlying this are largely undefined. Here we show that α-ketoglutarate (α-KG), a tricarboxylic acid cycle intermediate, extends the lifespan of adult Caenorhabditis elegans.

ATP synthase subunit β is identified as a novel binding protein of α-KG using a small-molecule target identification strategy termed drug affinity responsive target stability (DARTS). The ATP synthase, also known as complex V of the mitochondrial electron transport chain, is the main cellular energy-generating machinery and is highly conserved throughout evolution.

Although complete loss of mitochondrial function is detrimental, partial suppression of the electron transport chain has been shown to extend C. elegans lifespan.

We show that α-KG inhibits ATP synthase and, similar to ATP synthase knockdown, inhibition by α-KG leads to reduced ATP content, decreased oxygen consumption, and increased autophagy in both C. elegans and mammalian cells.

We provide evidence that the lifespan increase by α-KG requires ATP synthase subunit β and is dependent on target of rapamycin (TOR) downstream.

Endogenous α-KG levels are increased on starvation and α-KG does not extend the lifespan of dietary-restricted animals, indicating that α-KG is a key metabolite that mediates longevity by dietary restriction.

Our analyses uncover new molecular links between a common metabolite, a universal cellular energy generator and dietary restriction in the regulation of organismal lifespan, thus suggesting new strategies for the prevention and treatment of ageing and age-related diseases.

PMID: 24828042

 

 

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Larry H Bernstein, MD, FCAP, Contributor

Article ID #143: The Discovery and Properties of Avemar – Fermented Wheat Germ Extract: Carcinogenesis Suppressor. Published on 6/7/2014

WordCloud Image Produced by Adam Tubman

http://pharmaceuticalintelligence.com/5-6-2014/larryhbern/ The Discovery_and_Properties_of_Avemar – Fermented_ Wheat_Germ_Extract:_Carcinogenesis_Suppressor

The following discussion will be a review of the current interest in Avemar, a nontoxic, fermentation product of wheat germ extract, garnering interest with respect to alternative and complementary medicinal use.

Extracts from an interview by Sandra Cascio with Mate Hidvegi

Mate’s Transylvania Professor Lajos David was the organizer of the Department of Pharmacy of the University of Szeged in the 1920’s. He was elected as the Dean of the Faculty of Medicine, the first and only pharmacist who reached this high position at the University since. Dr. Hidvegy’s grandfather was a devout Roman catholic, who publicly opposed Nazi persecution of Jews during the Holocaust. One of his colleagues and, perhaps his best friend, was Albert Szent­Gyorgyi, the Nobel laureate who discovered vitaminC. Szent­Gyorgyi moved to the United States after World War II, where he turned to studies of muscle biochemistry. In his later years he turned to cancer research. He  theorized that a revolutionary anticancer drug could be based upon vitamin C combined with methoxy­substituted benzoquinones, the precursors of which can be found in wheat germ. After completion of the PhD, Dr. Hidvegi spent two years with the Wheat Grain Trust in Winnipeg, Canada, before returning to Hungary in 1990.  He decided to followthepathwaythat Szent­Gyorgyi was now engaged intocompletehisgoals.He contacted anoldfriend,GaborFodor, a brilliantchemist, also a collaborator withSzent­Gyorgyiincancerresearch.

He wasinvited by Hermann Esterbauer, the head of the Institute of Biochemistry at the University of Graz, to work in his laboratory. Thanks to the generosity of Professor Esterbauer,  he accomplished much at Graz  together with his student, Dr. Rita Farkas.  It was soon after Szent­-Gyorgyi’s death when, with the help of Dr. Fodor, they prepared the chemicals to make the drug Szent­-Gyorgyi had intended to make, with encouragement from the great quantum­ biochemist, Janos Ladik.  They made wheat germ extracts with the highest free benzoquinone content.This required a  fermentation process to liberate the benzoquinone moieties from the chemical bonds which keep them in natural forms: in glycosides. He recalls the purple colored active molecules in the fermentation liquid. Living cells with their exo­ and endo­enzymes are used to split bonds and make new molecules. This is also true for the manufacturing process of Avemar. This extract contains new molecules which cannot be found elsewhere.

“WhenAvemar was voted by the majority of the more than 50,000 professionals for NutrAward, it became obvious that this product is of biological efficacy  plus safety, and it is based on good science.” It received the financial support needed. From this, he was able to complete the experiments and get the approval for the registration. The time arrived when he really had to give a name to the product which had only had a code name. One late night it just came: Avemar, from the Latin prayer: Ave Maria.

Avemar with widely used chemotherapeutic drugs completely inhibited the development of metastases. Exploring its whole activity profile might even take a lifetime of research. So far he has supervised Avemar research done in Hungary, Israel, the United States, Austria, Italy, Spain, Slovakia, the Czech Republic, Germany,the United Kingdom, Russia, Australia, Korea, Vietnam. It has been a good experience to see the scientific interest it has generated worldwide. In 2009, Dr. Hidvegy received an invitation from the Nobel laureate, James Watson, co­discoverer of DNA’s double helix. It was a great honor. Avemar, he hopes,will be a significant cancer drug.

Mate Hidvegi was born in Budapest, Hungary, in 1955. He studied, then  taughat what is now Budapest University of Technology  and Economics.  After finishing university, he worked in the cereal industry and was co­developer of patented feed advisory system based on near infrared ingredient      data. In Hungary, Hidvegi was one of the pioneers in the development of           technologies for large ­scale production of instantized extracts for  therapeutic use.

 

Carcinogenesis vol.22 no.10 pp.1649–1652, 2001

Wheat germ extract inhibits experimental colon carcino-genesis in F-344 rats

Attila Zalatnai, Karoly Lapis, Bela Szende, Erzsebet Raso, Andros Telekes, Akos Resetar, and Mate Hidvegi

 

It has been demonstrated for the first time that a wheat germ extract prevents colonic cancer in laboratory animals. Four-week-old inbred male F-344 rats were used in the study. Colon carcinogenesis was induced by azoxy-methane (AOM). Ten rats served as untreated controls (group 1). For the treatment of the animals in group 2, AOM was dissolved in physiologic saline and the animals were given three weekly subcutaneous injections at 15 mg/kg body weight (b/w). In two additional groups Avemar (MSC), a fermented wheat germ extract standardized to 2,6-dimethoxy-p-benzoquinone was administered as a tentative chemo-preventive agent. MSC was dissolved in water and was given by gavage at a dose of 3 g/kg b/w once a day. In group 3, animals started to receive MSC 2 weeks prior to the first injection of AOM daily and continuously thereafter until they were killed 32 weeks later. In group 4 only the basal diet and MSC were administered. At the end of the experiment all the rats were exsanguinated under a light ether anesthesia and necropsied. Percentage of animals developing colon tumors and number of tumors per animals: group 1 – 0 and 0; group 2– 83.0 and 2.3; group 3 – 44.8 (P ≤ 0.001) and 1.3 (P ≤ 0.004); group 4 – 0 and 0. All the tumors were histologically neoplastic. The numbers of the aberrant crypt foci (ACF) per area (cm2) in group 2 were 4.85 while in group 3 the ACF numbers were 2.03 only (P ≤ 0.0001).
Table I. Macroscopic findings in the large intestines of F-344 rats treated with MSC or MSC +  AOM
No. of animals     w/tumorw   Average
# tumors
Average
diameter

N

1 Untreated
controls (10)
0/10 0/10
2.  AOM (47) 39/47
(83.0%)
2.3 ­+ 0.21
(range 1–8)
2.35 +
0.25
3.   MSC +
AOM (29)
13/29
(44.8%)
1.3 + 0.17
(range 1–3)
2.21 +
0.12
4.  MSC (9) 0/9 0/9
Fig. 1. Experimental schedule. Colon carcinogenesis was induced by three consecutive s.c. doses of AOM 1 week apart in F-344 rats. Oral administration of MSC was started 2 weeks before the carcinogen treatments. All the animals were killed at the end of the experiment, e.g. on the 32nd week.  (not shown)

 

Summing up, although the chemoprevention of colon cancers (and their pre-neoplastic lesions) has well and long been established and could be achieved by totally different compounds, the mechanisms have still remained to be clarified. This is also true for MSC.

The exact mechanism by which the fermented wheat germ concentration can prevent colon cancer is still partly unknown. MSC did inhibit the AOM-induced ACF and colon neoplasm formation, the multiplicity of the tumors, apparently acting in the initiation phase. Regarding this, we can hypothesize that MSC acts as an immunomodulator.

 

Wheat Germ Extract Decreases Glucose Uptake and RNARibose Formation but Increases Fatty Acid Synthesis in MIAPancreatic Adenocarcinoma Cell

LG Boros, K Lapis, B Szende, R Tömösközi-Farkas, Ádám Balogh, …., and M Hidvégi

UCLA School of Medicine, Harbor-UCLA Research and Education Institute, Torrance, Ca.; First Institute of Pathology and Experimental Cancer Research, Semmelweis  Medical University, Budapest, Hungary; Central Food Research Institute, Budapest, Hungary; Department of Surgery, Albert Szent-Gyorgyi Medical and Pharmaceutical Center, School of General Medicine, University of Szeged, Szeged, Hungary; Department of Biochemistry and Molecular Biology, Institut d’Investigacions Biomediques August Pi i Sunyer, University of Barcelona, Barcelona, Spain; andDepartment of Biochemistryand Food Technology, Technical University of Budapest and Biromedicina Company, Budapest, Hungary

Pancreas 2001; 23 (2), pp. 141–147

Summary: The fermented wheat germ extract with standardized composition has potent tumor inhibitory properties. The fermented wheat germ extract controls tumor propagation. The authors show that this extract induces profound metabolic changes in cultured MIA pancreatic adenocarcinoma cells when the [1,2- 13C2] glucose isotope is used as the single tracer with biologic gas chromatography–mass spectrometry.

MIA cells treated with 0.1, 1, and 10 mg/mL wheat  germ extract showed a dose-dependent decrease in cell glucose consumption, consumption, uptake of isotope into ribosomal RNA (2.4%, 9.4%, and 8.0%), and release of 13CO2 . Conversely, direct glucose oxidation and ribose recycling in the pentose cycle showed a dose-dependent increase of 1.2%, 20.7%, and 93.4%. The newly synthesized fraction of cell palmitate and the 13C enrichment of acetyl units were also increased with all doses of wheat germ extract.

The fermented wheat germ extract controls tumor propagation primarily by regulating glucose carbon redistribution between cell proliferation–related and cell differentiation–related macromolecules. Wheat germ extract treatment is likely associated with the phosphor-ylation and transcriptional regulation of metabolic enzymes that are involved in glucose carbon redistribution between cell the direct oxidative degradation of glucose,proliferation–related structural and functional macromolecules(RNA, DNA) and the direct oxidative degradation and survival of pancreatic adenocarcinoma cells in culture.

Key Words: Pentose cycle—Ribose synthesis—Fermented wheat germ extract—Nonoxidative glucose metabolism—Cell proliferation—Avemar.

 

Fig 1 glu consumption of MIA pancreatic carcinoma cells in response to WGE

Fig 1 glu consumption of MIA pancreatic carcinoma cells in response to WGE

 

 

 

 

 

 

 

 

 

 

 

Figure 1. Glucose consumption of MIA pancreatic adenocarcinoma cells in response to increasing doses of fermented wheat germ extract (Avemar) treatment after 72 hours of culture. Glucose consumption (measured in milligrams) was estimated by the difference in media glucose content between Avemar-treated and control cultures. MIA cell glucose consumption was significantly inhibited in the presence of either 1 mg/mL (*p < 0.05) or 10 mg/mL (**p < 0.01) Avemar (x + SD;  n = 6).

 

fig-3-rna-syn-of-mia-pancreatic-carcinoma-cells-in-response-to-wge.jpg

fig-3-rna-syn-of-mia-pancreatic-carcinoma-cells-in-response-to-wge.jpg

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Ribosomal RNA synthesis of MIA pancreatic adenocarcinoma cells in response to increasing doses of fermented wheat germ extract (Avemar) treatment after 72 hours of culture. Glucose carbon incorporation into ribose isolated from ribosomal RNA is expressed as molar enrichment. The dose-dependent decrease in of rRNA after Avemar treatment indicates that ribosomal RNA synthesis is the primary site significantly affected by all doses of Avemar treatment with a maximum decrease of 29% after 10 mg/mL treatment (x + SD; n = 9; *p < 0.05, **p < 0.01).

changes in metabolic activity indicate that Avemar treatment affects cell metabolism primarily by decreasing glucose uptake and nucleic acid ribose synthesis while increasing glucose oxidation through the oxidative reactions of the pentose cycle and fatty acid  synthesis from glucose carbon. The effect of Avemar treatment on lactate production and TCA cycle anapleurotic flux compared with glucose oxidation is less prominent

 

Fermented wheat germ extract induces apoptosis and downregulation of major histocompatibility complex class I proteins in tumor T and B cell lines

R FAJKA-BOJA, M HIDVÉGI, Y SHOENFELD, G  ION, D DEMYDENKO, R TÖMÖSKÖZI-FARKAS, et al.

INTL J ONCOLOGY 2002; 20: 563-570.

Lymphocyte Signal Transduction Laboratory, Institute of Genetics, and Cytokine Group, Institute of Biochemistry, Biological Research Center of the Hungarian Academy of Sciences, Szeged; Department of Biochemistry and Food Technology, Budapest University of Technology and Economics, Budapest, Hungary; Department of Medicine ‘B’, Center for Autoimmune Diseases, Sheba Medical Center, Tel-Hashomer, Israel; Central Food Research Institute; National Institute of Oncology; Biromedicina Co., Budapest, Hungary
Abstract. The fermented wheat germ extract (code name:  on cyto-fluorimeter using a monoclonal antibody to the  MSC, trade name: Avemar), with standardized benzoquinone non-polymorphic region of the human MHC class I. MSC  content has been shown to inhibit tumor propagation and stimulated tyrosine phosphorylation of intracellular proteins metastases formation in vivo. The aim of this study was to  understand the molecular and cellular mechanisms of the anti-tumor effect of MSC. Therefore, we have designed in vitro model experiments using T and B tumor lymphocytic cell lines. As a result of the MSC treatment, cell surface MHC class I proteins was downregulated by 70-85% compared to the non-stimulated control.

Prominent apoptosis of and the influx of extracellular Ca2+ resulted in elevation of the amount of the intracellular Ca2+ concentration. 20-40% was detected upon 24 h of MSC treatment of the cell lines. Apoptosis was measured with cytofluorimetry by staining the DNA with propidium iodide and detecting the ‘sub-G ’ cell population.

Tyrosine phosphorylation of intra-cellular proteins and elevation of the intracellular Ca2+ concentration were examined using immunoblotting with anti-phosphotyrosine antibody and cytofluorimetry by means of Ca2+ sensitive fluorescence dyes, Fluo-3AM and FuraRed-AM, respectively. MSC did not induce a similar degree of apoptosis in healthy peripheral blood mononuclear cells.

Inhibition of the cellular tyrosine phosphatase activity or Ca2+ influx resulted in the opposite effect – increasing or diminishing the Avemar induced apoptosis as well as the MHC class I downregulation. The level of the cell surface MHC class I molecules was analysed with indirect immunofluorescence. The benzoquinone component (2,6-dimethoxi-p-benzoquinone) in MSC induced similar apoptosis and downregulation of the MHC class I molecules in the tumor T and B cell lines to that of MSC. These results suggest that MSC acts on lymphoid tumor cells by reducing MHC class I expression and selectively promoting apoptosis of tumor cells on a tyrosine phosphorylation and Ca2+ influx dependent way.  One of the components in MSC, 2,6-dimethoxi-p-benzoquinone was shown to be an important factor in MSC mediated cell response.

 

Abbreviations:MHC, major histocompatibility complex;NK, natural killer;DMBQ, 2,6-dimethoxi-p-benzoquinone; FCS, fetal calf serum;PBMC, peripheral bloodmononuclear cells; TCR, T cell receptor;BCR, B cell receptor; mAb, monoclonal antibody;PMSF,phenylmethyl-sulfonylfluoride;pNPP, para-nitrophenyl-phosphate; PHA,phytohemagglutinineKey words: fermented wheat germ extract, Avemar, MSC, 2+ benzoquinone, tyrosine phosphorylation, intracellular Ca , CD45, tyrosine phosphatase, MHC class I downregulation, apoptosis

 

fig-4-apoptosis-of-t-cell-lines-induced-by-avamer.jpg

fig-4-apoptosis-of-t-cell-lines-induced-by-avamer.jpg

 

 

 

 

 

Figure 4. Apoptosis of tumor T cell lines and healthy lymphocytes upon MSC treatment. Jurkat cells were treated with 1 mg/ml MSC or .3 µg/ml DMBQ and PBMC were treated with 1 mg/ml
MSC for 24 h (A) or Jurkat cells were treated for 12 h (thick line in panel B). Control cells were left unstimulated (black bars in panel A or thin line on panel B). Apoptotic cells were enumerated
with the DNA analysis of the ‘sub-G ’ population (A) or with staining the cells with FITC1 labeled Annexin V
(B). Representative experiments are shown. The difference between the % of apoptosis in the case of treated and non-treated Jurkat cells was significant (MSC, p<0.001, n=14; DMBQ, p<0.05, n=3,
using  paired, two-tailed t-test). No difference was found for PBMC (n=2).

MSC treatment causes prominent apoptosis in lymphoid tumor cells but it does not induce apoptosis of healthy resting mononuclear cells. Moreover, although MSC blocks the proliferation of PBM cells stimulated with PHA, it does not induce apoptosis in PHA stimulated cells (data not shown).

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Summary of Translational Medicine – e-Series A: Cardiovascular Diseases, Volume Four – Part 1

Summary of Translational Medicine – e-Series A: Cardiovascular Diseases, Volume Four – Part 1

Author and Curator: Larry H Bernstein, MD, FCAP

and

Curator: Aviva Lev-Ari, PhD, RN

Article ID #135: Summary of Translational Medicine – e-Series A: Cardiovascular Diseases, Volume Four – Part 1. Published on 4/28/2014

WordCloud Image Produced by Adam Tubman

 

Part 1 of Volume 4 in the e-series A: Cardiovascular Diseases and Translational Medicine, provides a foundation for grasping a rapidly developing surging scientific endeavor that is transcending laboratory hypothesis testing and providing guidelines to:

  • Target genomes and multiple nucleotide sequences involved in either coding or in regulation that might have an impact on complex diseases, not necessarily genetic in nature.
  • Target signaling pathways that are demonstrably maladjusted, activated or suppressed in many common and complex diseases, or in their progression.
  • Enable a reduction in failure due to toxicities in the later stages of clinical drug trials as a result of this science-based understanding.
  • Enable a reduction in complications from the improvement of machanical devices that have already had an impact on the practice of interventional procedures in cardiology, cardiac surgery, and radiological imaging, as well as improving laboratory diagnostics at the molecular level.
  • Enable the discovery of new drugs in the continuing emergence of drug resistance.
  • Enable the construction of critical pathways and better guidelines for patient management based on population outcomes data, that will be critically dependent on computational methods and large data-bases.

What has been presented can be essentially viewed in the following Table:

 

Summary Table for TM - Part 1

Summary Table for TM – Part 1

 

 

 

There are some developments that deserve additional development:

1. The importance of mitochondrial function in the activity state of the mitochondria in cellular work (combustion) is understood, and impairments of function are identified in diseases of muscle, cardiac contraction, nerve conduction, ion transport, water balance, and the cytoskeleton – beyond the disordered metabolism in cancer.  A more detailed explanation of the energetics that was elucidated based on the electron transport chain might also be in order.

2. The processes that are enabling a more full application of technology to a host of problems in the environment we live in and in disease modification is growing rapidly, and will change the face of medicine and its allied health sciences.

 

Electron Transport and Bioenergetics

Deferred for metabolomics topic

Synthetic Biology

Introduction to Synthetic Biology and Metabolic Engineering

Kristala L. J. Prather: Part-1    <iBiology > iBioSeminars > Biophysics & Chemical Biology >

http://www.ibiology.org Lecturers generously donate their time to prepare these lectures. The project is funded by NSF and NIGMS, and is supported by the ASCB and HHMI.
Dr. Prather explains that synthetic biology involves applying engineering principles to biological systems to build “biological machines”.

Dr. Prather has received numerous awards both for her innovative research and for excellence in teaching.  Learn more about how Kris became a scientist at
Prather 1: Synthetic Biology and Metabolic Engineering  2/6/14IntroductionLecture Overview In the first part of her lecture, Dr. Prather explains that synthetic biology involves applying engineering principles to biological systems to build “biological machines”. The key material in building these machines is synthetic DNA. Synthetic DNA can be added in different combinations to biological hosts, such as bacteria, turning them into chemical factories that can produce small molecules of choice. In Part 2, Prather describes how her lab used design principles to engineer E. coli that produce glucaric acid from glucose. Glucaric acid is not naturally produced in bacteria, so Prather and her colleagues “bioprospected” enzymes from other organisms and expressed them in E. coli to build the needed enzymatic pathway. Prather walks us through the many steps of optimizing the timing, localization and levels of enzyme expression to produce the greatest yield. Speaker Bio: Kristala Jones Prather received her S.B. degree from the Massachusetts Institute of Technology and her PhD at the University of California, Berkeley both in chemical engineering. Upon graduation, Prather joined the Merck Research Labs for 4 years before returning to academia. Prather is now an Associate Professor of Chemical Engineering at MIT and an investigator with the multi-university Synthetic Biology Engineering Reseach Center (SynBERC). Her lab designs and constructs novel synthetic pathways in microorganisms converting them into tiny factories for the production of small molecules. Dr. Prather has received numerous awards both for her innovative research and for excellence in teaching.

VIEW VIDEOS

https://www.youtube.com/watch?feature=player_embedded&v=ndThuqVumAk#t=0

https://www.youtube.com/watch?feature=player_embedded&v=ndThuqVumAk#t=12

https://www.youtube.com/watch?feature=player_embedded&v=ndThuqVumAk#t=74

https://www.youtube.com/watch?feature=player_embedded&v=ndThuqVumAk#t=129

https://www.youtube.com/watch?feature=player_embedded&v=ndThuqVumAk#t=168

https://www.youtube.com/watch?feature=player_embedded&v=ndThuqVumAk

 

II. Regulatory Effects of Mammalian microRNAs

Calcium Cycling in Synthetic and Contractile Phasic or Tonic Vascular Smooth Muscle Cells

in INTECH
Current Basic and Pathological Approaches to
the Function of Muscle Cells and Tissues – From Molecules to HumansLarissa Lipskaia, Isabelle Limon, Regis Bobe and Roger Hajjar
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/48240
1. Introduction
Calcium ions (Ca ) are present in low concentrations in the cytosol (~100 nM) and in high concentrations (in mM range) in both the extracellular medium and intracellular stores (mainly sarco/endo/plasmic reticulum, SR). This differential allows the calcium ion messenger that carries information
as diverse as contraction, metabolism, apoptosis, proliferation and/or hypertrophic growth. The mechanisms responsible for generating a Ca signal greatly differ from one cell type to another.
In the different types of vascular smooth muscle cells (VSMC), enormous variations do exist with regard to the mechanisms responsible for generating Ca signal. In each VSMC phenotype (synthetic/proliferating and contractile [1], tonic or phasic), the Ca signaling system is adapted to its particular function and is due to the specific patterns of expression and regulation of Ca.
For instance, in contractile VSMCs, the initiation of contractile events is driven by mem- brane depolarization; and the principal entry-point for extracellular Ca is the voltage-operated L-type calcium channel (LTCC). In contrast, in synthetic/proliferating VSMCs, the principal way-in for extracellular Ca is the store-operated calcium (SOC) channel.
Whatever the cell type, the calcium signal consists of  limited elevations of cytosolic free calcium ions in time and space. The calcium pump, sarco/endoplasmic reticulum Ca ATPase (SERCA), has a critical role in determining the frequency of SR Ca release by upload into the sarcoplasmic
sensitivity of  SR calcium channels, Ryanodin Receptor, RyR and Inositol tri-Phosphate Receptor, IP3R.
Synthetic VSMCs have a fibroblast appearance, proliferate readily, and synthesize increased levels of various extracellular matrix components, particularly fibronectin, collagen types I and III, and tropoelastin [1].
Contractile VSMCs have a muscle-like or spindle-shaped appearance and well-developed contractile apparatus resulting from the expression and intracellular accumulation of thick and thin muscle filaments [1].
Schematic representation of Calcium Cycling in Contractile and Proliferating VSMCs

Schematic representation of Calcium Cycling in Contractile and Proliferating VSMCs

 

Figure 1. Schematic representation of Calcium Cycling in Contractile and Proliferating VSMCs.

Left panel: schematic representation of calcium cycling in quiescent /contractile VSMCs. Contractile re-sponse is initiated by extracellular Ca influx due to activation of Receptor Operated Ca (through phosphoinositol-coupled receptor) or to activation of L-Type Calcium channels (through an increase in luminal pressure). Small increase of cytosolic due IP3 binding to IP3R (puff) or RyR activation by LTCC or ROC-dependent Ca influx leads to large SR Ca IP3R or RyR clusters (“Ca -induced Ca SR calcium pumps (both SERCA2a and SERCA2b are expressed in quiescent VSMCs), maintaining high concentration of cytosolic Ca and setting the sensitivity of RyR or IP3R for the next spike.
Contraction of VSMCs occurs during oscillatory Ca transient.
Middle panel: schematic representa tion of atherosclerotic vessel wall. Contractile VSMC are located in the media layer, synthetic VSMC are located in sub-endothelial intima.
Right panel: schematic representation of calcium cycling in quiescent /contractile VSMCs. Agonist binding to phosphoinositol-coupled receptor leads to the activation of IP3R resulting in large increase in cytosolic Ca calcium pumps (only SERCA2b, having low turnover and low affinity to Ca depletion leads to translocation of SR Ca sensor STIM1 towards PM, resulting in extracellular Ca influx though opening of Store Operated Channel (CRAC). Resulted steady state Ca transient is critical for activation of proliferation-related transcription factors ‘NFAT).
Abbreviations: PLC – phospholipase C; PM – plasma membrane; PP2B – Ca /calmodulin-activated protein phosphatase 2B (calcineurin); ROC- receptor activated channel; IP3 – inositol-1,4,5-trisphosphate, IP3R – inositol-1,4,5- trisphosphate receptor; RyR – ryanodine receptor; NFAT – nuclear factor of activated T-lymphocytes; VSMC – vascular smooth muscle cells; SERCA – sarco(endo)plasmic reticulum Ca sarcoplasmic reticulum.

 

Time for New DNA Synthesis and Sequencing Cost Curves

By Rob Carlson

I’ll start with the productivity plot, as this one isn’t new. For a discussion of the substantial performance increase in sequencing compared to Moore’s Law, as well as the difficulty of finding this data, please see this post. If nothing else, keep two features of the plot in mind: 1) the consistency of the pace of Moore’s Law and 2) the inconsistency and pace of sequencing productivity. Illumina appears to be the primary driver, and beneficiary, of improvements in productivity at the moment, especially if you are looking at share prices. It looks like the recently announced NextSeq and Hiseq instruments will provide substantially higher productivities (hand waving, I would say the next datum will come in another order of magnitude higher), but I think I need a bit more data before officially putting another point on the plot.

 

cost-of-oligo-and-gene-synthesis

cost-of-oligo-and-gene-synthesis

Illumina’s instruments are now responsible for such a high percentage of sequencing output that the company is effectively setting prices for the entire industry. Illumina is being pushed by competition to increase performance, but this does not necessarily translate into lower prices. It doesn’t behoove Illumina to drop prices at this point, and we won’t see any substantial decrease until a serious competitor shows up and starts threatening Illumina’s market share. The absence of real competition is the primary reason sequencing prices have flattened out over the last couple of data points.

Note that the oligo prices above are for column-based synthesis, and that oligos synthesized on arrays are much less expensive. However, array synthesis comes with the usual caveat that the quality is generally lower, unless you are getting your DNA from Agilent, which probably means you are getting your dsDNA from Gen9.

Note also that the distinction between the price of oligos and the price of double-stranded sDNA is becoming less useful. Whether you are ordering from Life/Thermo or from your local academic facility, the cost of producing oligos is now, in most cases, independent of their length. That’s because the cost of capital (including rent, insurance, labor, etc) is now more significant than the cost of goods. Consequently, the price reflects the cost of capital rather than the cost of goods. Moreover, the cost of the columns, reagents, and shipping tubes is certainly more than the cost of the atoms in the sDNA you are ostensibly paying for. Once you get into longer oligos (substantially larger than 50-mers) this relationship breaks down and the sDNA is more expensive. But, at this point in time, most people aren’t going to use longer oligos to assemble genes unless they have a tricky job that doesn’t work using short oligos.

Looking forward, I suspect oligos aren’t going to get much cheaper unless someone sorts out how to either 1) replace the requisite human labor and thereby reduce the cost of capital, or 2) finally replace the phosphoramidite chemistry that the industry relies upon.

IDT’s gBlocks come at prices that are constant across quite substantial ranges in length. Moreover, part of the decrease in price for these products is embedded in the fact that you are buying smaller chunks of DNA that you then must assemble and integrate into your organism of choice.

Someone who has purchased and assembled an absolutely enormous amount of sDNA over the last decade, suggested that if prices fell by another order of magnitude, he could switch completely to outsourced assembly. This is a potentially interesting “tipping point”. However, what this person really needs is sDNA integrated in a particular way into a particular genome operating in a particular host. The integration and testing of the new genome in the host organism is where most of the cost is. Given the wide variety of emerging applications, and the growing array of hosts/chassis, it isn’t clear that any given technology or firm will be able to provide arbitrary synthetic sequences incorporated into arbitrary hosts.

 TrackBack URL: http://www.synthesis.cc/cgi-bin/mt/mt-t.cgi/397

 

Startup to Strengthen Synthetic Biology and Regenerative Medicine Industries with Cutting Edge Cell Products

28 Nov 2013 | PR Web

Dr. Jon Rowley and Dr. Uplaksh Kumar, Co-Founders of RoosterBio, Inc., a newly formed biotech startup located in Frederick, are paving the way for even more innovation in the rapidly growing fields of Synthetic Biology and Regenerative Medicine. Synthetic Biology combines engineering principles with basic science to build biological products, including regenerative medicines and cellular therapies. Regenerative medicine is a broad definition for innovative medical therapies that will enable the body to repair, replace, restore and regenerate damaged or diseased cells, tissues and organs. Regenerative therapies that are in clinical trials today may enable repair of damaged heart muscle following heart attack, replacement of skin for burn victims, restoration of movement after spinal cord injury, regeneration of pancreatic tissue for insulin production in diabetics and provide new treatments for Parkinson’s and Alzheimer’s diseases, to name just a few applications.

While the potential of the field is promising, the pace of development has been slow. One main reason for this is that the living cells required for these therapies are cost-prohibitive and not supplied at volumes that support many research and product development efforts. RoosterBio will manufacture large quantities of standardized primary cells at high quality and low cost, which will quicken the pace of scientific discovery and translation to the clinic. “Our goal is to accelerate the development of products that incorporate living cells by providing abundant, affordable and high quality materials to researchers that are developing and commercializing these regenerative technologies” says Dr. Rowley

 

Life at the Speed of Light

http://kcpw.org/?powerpress_pinw=92027-podcast

NHMU Lecture featuring – J. Craig Venter, Ph.D.
Founder, Chairman, and CEO – J. Craig Venter Institute; Co-Founder and CEO, Synthetic Genomics Inc.

J. Craig Venter, Ph.D., is Founder, Chairman, and CEO of the J. Craig Venter Institute (JVCI), a not-for-profit, research organization dedicated to human, microbial, plant, synthetic and environmental research. He is also Co-Founder and CEO of Synthetic Genomics Inc. (SGI), a privately-held company dedicated to commercializing genomic-driven solutions to address global needs.

In 1998, Dr. Venter founded Celera Genomics to sequence the human genome using new tools and techniques he and his team developed.  This research culminated with the February 2001 publication of the human genome in the journal, Science. Dr. Venter and his team at JVCI continue to blaze new trails in genomics.  They have sequenced and a created a bacterial cell constructed with synthetic DNA,  putting humankind at the threshold of a new phase of biological research.  Whereas, we could  previously read the genetic code (sequencing genomes), we can now write the genetic code for designing new species.

The science of synthetic genomics will have a profound impact on society, including new methods for chemical and energy production, human health and medical advances, clean water, and new food and nutritional products. One of the most prolific scientists of the 21st century for his numerous pioneering advances in genomics,  he  guides us through this emerging field, detailing its origins, current challenges, and the potential positive advances.

His work on synthetic biology truly embodies the theme of “pushing the boundaries of life.”  Essentially, Venter is seeking to “write the software of life” to create microbes designed by humans rather than only through evolution. The potential benefits and risks of this new technology are enormous. It also requires us to examine, both scientifically and philosophically, the question of “What is life?”

J Craig Venter wants to digitize DNA and transmit the signal to teleport organisms

http://pharmaceuticalintelligence.com/2013/11/01/j-craig-venter-wants-to-digitize-dna-and-transmit-the-signal-to-teleport-organisms/

2013 Genomics: The Era Beyond the Sequencing of the Human Genome: Francis Collins, Craig Venter, Eric Lander, et al.

http://pharmaceuticalintelligence.com/2013/02/11/2013-genomics-the-era-beyond-the-sequencing-human-genome-francis-collins-craig-venter-eric-lander-et-al/

Human Longevity Inc (HLI) – $70M in Financing of Venter’s New Integrative Omics and Clinical Bioinformatics

http://pharmaceuticalintelligence.com/2014/03/05/human-longevity-inc-hli-70m-in-financing-of-venters-new-integrative-omics-and-clinical-bioinformatics/

 

 

Where Will the Century of Biology Lead Us?

By Randall Mayes

A technology trend analyst offers an overview of synthetic biology, its potential applications, obstacles to its development, and prospects for public approval.

  • In addition to boosting the economy, synthetic biology projects currently in development could have profound implications for the future of manufacturing, sustainability, and medicine.
  • Before society can fully reap the benefits of synthetic biology, however, the field requires development and faces a series of hurdles in the process. Do researchers have the scientific know-how and technical capabilities to develop the field?

Biology + Engineering = Synthetic Biology

Bioengineers aim to build synthetic biological systems using compatible standardized parts that behave predictably. Bioengineers synthesize DNA parts—oligonucleotides composed of 50–100 base pairs—which make specialized components that ultimately make a biological system. As biology becomes a true engineering discipline, bioengineers will create genomes using mass-produced modular units similar to the microelectronics and computer industries.

Currently, bioengineering projects cost millions of dollars and take years to develop products. For synthetic biology to become a Schumpeterian revolution, smaller companies will need to be able to afford to use bioengineering concepts for industrial applications. This will require standardized and automated processes.

A major challenge to developing synthetic biology is the complexity of biological systems. When bioengineers assemble synthetic parts, they must prevent cross talk between signals in other biological pathways. Until researchers better understand these undesired interactions that nature has already worked out, applications such as gene therapy will have unwanted side effects. Scientists do not fully understand the effects of environmental and developmental interaction on gene expression. Currently, bioengineers must repeatedly use trial and error to create predictable systems.

Similar to physics, synthetic biology requires the ability to model systems and quantify relationships between variables in biological systems at the molecular level.

The second major challenge to ensuring the success of synthetic biology is the development of enabling technologies. With genomes having billions of nucleotides, this requires fast, powerful, and cost-efficient computers. Moore’s law, named for Intel co-founder Gordon Moore, posits that computing power progresses at a predictable rate and that the number of components in integrated circuits doubles each year until its limits are reached. Since Moore’s prediction, computer power has increased at an exponential rate while pricing has declined.

DNA sequencers and synthesizers are necessary to identify genes and make synthetic DNA sequences. Bioengineer Robert Carlson calculated that the capabilities of DNA sequencers and synthesizers have followed a pattern similar to computing. This pattern, referred to as the Carlson Curve, projects that scientists are approaching the ability to sequence a human genome for $1,000, perhaps in 2020. Carlson calculated that the costs of reading and writing new genes and genomes are falling by a factor of two every 18–24 months. (see recent Carlson comment on requirement to read and write for a variety of limiting  conditions).

Startup to Strengthen Synthetic Biology and Regenerative Medicine Industries with Cutting Edge Cell Products

http://pharmaceuticalintelligence.com/2013/11/28/startup-to-strengthen-synthetic-biology-and-regenerative-medicine-industries-with-cutting-edge-cell-products/

Synthetic Biology: On Advanced Genome Interpretation for Gene Variants and Pathways: What is the Genetic Base of Atherosclerosis and Loss of Arterial Elasticity with Aging

http://pharmaceuticalintelligence.com/2013/05/17/synthetic-biology-on-advanced-genome-interpretation-for-gene-variants-and-pathways-what-is-the-genetic-base-of-atherosclerosis-and-loss-of-arterial-elasticity-with-aging/

Synthesizing Synthetic Biology: PLOS Collections

http://pharmaceuticalintelligence.com/2012/08/17/synthesizing-synthetic-biology-plos-collections/

Capturing ten-color ultrasharp images of synthetic DNA structures resembling numerals 0 to 9

http://pharmaceuticalintelligence.com/2014/02/05/capturing-ten-color-ultrasharp-images-of-synthetic-dna-structures-resembling-numerals-0-to-9/

Silencing Cancers with Synthetic siRNAs

http://pharmaceuticalintelligence.com/2013/12/09/silencing-cancers-with-synthetic-sirnas/

Genomics Now—and Beyond the Bubble

Futurists have touted the twenty-first century as the century of biology based primarily on the promise of genomics. Medical researchers aim to use variations within genes as biomarkers for diseases, personalized treatments, and drug responses. Currently, we are experiencing a genomics bubble, but with advances in understanding biological complexity and the development of enabling technologies, synthetic biology is reviving optimism in many fields, particularly medicine.

BY MICHAEL BROOKS    17 APR, 2014     http://www.newstatesman.com/

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is The Secret Anarchy of Science.

The basic idea is that we take an organism – a bacterium, say – and re-engineer its genome so that it does something different. You might, for instance, make it ingest carbon dioxide from the atmosphere, process it and excrete crude oil.

That project is still under construction, but others, such as using synthesised DNA for data storage, have already been achieved. As evolution has proved, DNA is an extraordinarily stable medium that can preserve information for millions of years. In 2012, the Harvard geneticist George Church proved its potential by taking a book he had written, encoding it in a synthesised strand of DNA, and then making DNA sequencing machines read it back to him.

When we first started achieving such things it was costly and time-consuming and demanded extraordinary resources, such as those available to the millionaire biologist Craig Venter. Venter’s team spent most of the past two decades and tens of millions of dollars creating the first artificial organism, nicknamed “Synthia”. Using computer programs and robots that process the necessary chemicals, the team rebuilt the genome of the bacterium Mycoplasma mycoides from scratch. They also inserted a few watermarks and puzzles into the DNA sequence, partly as an identifying measure for safety’s sake, but mostly as a publicity stunt.

What they didn’t do was redesign the genome to do anything interesting. When the synthetic genome was inserted into an eviscerated bacterial cell, the new organism behaved exactly the same as its natural counterpart. Nevertheless, that Synthia, as Venter put it at the press conference to announce the research in 2010, was “the first self-replicating species we’ve had on the planet whose parent is a computer” made it a standout achievement.

Today, however, we have entered another era in synthetic biology and Venter faces stiff competition. The Steve Jobs to Venter’s Bill Gates is Jef Boeke, who researches yeast genetics at New York University.

Boeke wanted to redesign the yeast genome so that he could strip out various parts to see what they did. Because it took a private company a year to complete just a small part of the task, at a cost of $50,000, he realised he should go open-source. By teaching an undergraduate course on how to build a genome and teaming up with institutions all over the world, he has assembled a skilled workforce that, tinkering together, has made a synthetic chromosome for baker’s yeast.

 

Stepping into DIYbio and Synthetic Biology at ScienceHack

Posted April 22, 2014 by Heather McGaw and Kyrie Vala-Webb

We got a crash course on genetics and protein pathways, and then set out to design and build our own pathways using both the “Genomikon: Violacein Factory” kit and Synbiota platform. With Synbiota’s software, we dragged and dropped the enzymes to create the sequence that we were then going to build out. After a process of sketching ideas, mocking up pathways, and writing hypotheses, we were ready to start building!

The night stretched long, and at midnight we were forced to vacate the school. Not quite finished, we loaded our delicate bacteria, incubator, and boxes of gloves onto the bus and headed back to complete our bacterial transformation in one of our hotel rooms. Jammed in between the beds and the mini-fridge, we heat-shocked our bacteria in the hotel ice bucket. It was a surreal moment.

While waiting for our bacteria, we held an “unconference” where we explored bioethics, security and risk related to synthetic biology, 3D printing on Mars, patterns in juggling (with live demonstration!), and even did a Google Hangout with Rob Carlson. Every few hours, we would excitedly check in on our bacteria, looking for bacterial colonies and the purple hue characteristic of violacein.

Most impressive was the wildly successful and seamless integration of a diverse set of people: in a matter of hours, we were transformed from individual experts and practitioners in assorted fields into cohesive and passionate teams of DIY biologists and science hackers. The ability of everyone to connect and learn was a powerful experience, and over the course of just one weekend we were able to challenge each other and grow.

Returning to work on Monday, we were hungry for more. We wanted to find a way to bring the excitement and energy from the weekend into the studio and into the projects we’re working on. It struck us that there are strong parallels between design and DIYbio, and we knew there was an opportunity to bring some of the scientific approaches and curiosity into our studio.

 

 

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Prologue to Cancer – e-book Volume One – Where are we in this journey?

Prologue to Cancer – e-book Volume One – Where are we in this journey?

Author and Curator: Larry H. Bernstein, MD, FCAP

Article ID #128: Prologue to Cancer – e-book Volume One – Where are we in this journey? Published on 4/13/2014

WordCloud Image Produced by Adam Tubman

Consulting Reviewer and Contributor:  Jose Eduardo de Salles Roselino, MD

 

LH Bernstein

LH Bernstein

Jose Eduardo de Salles Roselino

LES Roselino

 

 

This is a preface to the fourth in the ebook series of Leaders in Pharmaceutical Intelligence, a collaboration of experienced doctorate medical and pharmaceutical professionals.  The topic is of great current interest, and it entails a significant part of current medical expenditure by a group of neoplastic diseases that may develop at different periods in life, and have come to supercede infections or even eventuate in infectious disease as an end of life event.  The articles presented are a collection of the most up-to-date accounts of the state of a now rapidly emerging field of medical research that has benefitted enormously by progress in immunodiagnostics,  radiodiagnostics, imaging, predictive analytics, genomic and proteomic discovery subsequent to the completion of the Human Genome Project, advances in analytic methods in qPCR, gene sequencing, genome mapping, signaling pathways, exome identification, identification of therapeutic targets in inhibitors, activators, initiators in the progression of cell metabolism, carcinogenesis, cell movement, and metastatic potential.  This story is very complicated because we are engaged in trying to evoke from what we would like to be similar clinical events, dissimilar events in their expression and classification, whether they are within the same or different anatomic class.  Thus, we are faced with constructing an objective evidence-based understanding requiring integration of several disciplinary approaches to see a clear picture.  The failure to do so creates a high risk of failure in biopharmaceutical development.

The chapters that follow cover novel and important research and development in cancer related research, development, diagnostics and treatment, and in balance, present a substantial part of the tumor landscape, with some exceptions.  Will there ever be a unifying concept, as might be hoped for? I certainly can’t see any such prediction on the horizon.  Part of the problem is that disease classification is a human construct to guide us, and so are treatments that have existed and are reexamined for over 2,000 years.  In that time, we have changed, our afflictions have been modified, and our environment has changed with respect to the microorganisms within and around us, viruses, the soil, and radiation exposure, and the impacts of war and starvation, and access to food.  The outline has been given.  Organic and inorganic chemistry combined with physics has given us a new enterprise in biosynthetics that is and will change our world.  But let us keep in mind that this is a human construct, just as drug target development is such a construct, workable with limitations.

What Molecular Biology Gained from Physics

We need greater clarity and completeness in defining the carcinogenetic process.  It is the beginning, but not the end.  But we must first examine the evolution of the scientific structure that leads to our present understanding. This was preceded by the studies of anatomy, physiology, and embryology that had to occur as a first step, which was followed by the researches into bacteriology, fungi, sea urchins and the evolutionary creatures that could be studied having more primary development in scale.  They are still major objects of study, with the expectation that we can derive lessons about comparative mechanisms that have been passed on through the ages and have common features with man.  This became the serious intent of molecular biology, the discipline that turned to find an explanation for genetics, and to carry out controlled experiments modelled on the discipline that already had enormous success in physics, mathematics, and chemistry. In 1900, when Max Planck hypothesized that the frequency of light emitted by the black body depended on the frequency of the oscillator that emitted it, it had important ramifications for chemistry and biology (See Appendix II and Footnote 1, Planck equation, energy and oscillation).  The leading idea is to search below the large-scale observations of classical biology.

The central dogma of molecular biology where genetic material is transcribed into RNA and then translated into protein, provides a starting point, but the construct is undergoing revision in light of emerging novel roles for RNA and signaling pathways.   The term, coined by Warren Weaver (director of Natural Sciences for the Rockefeller Foundation), who observed an emergence of significant change given recent advances in fields such as X-ray crystallography. Molecular biology also plays important role in understanding formations, actions, regulations of various parts of cellswhich can be used efficiently for targeting new drugs, diagnosis of disease, physiology of the Cell. The Nobel Prize in Physiology or Medicine in 1969 was shared by Max Delbrück, Alfred D. Hershey, Salvador E. Luria, whose work with viral replication gave impetus to the field.  Delbruck was a physicist who trained in Copenhagen under Bohr, and specifically committed himself to a rigor in biology, as was in physics.

Dorothy Hodgkin protein crystallography

Dorothy Hodgkin protein crystallography

Rosalind Franlin crystallographer double helix

Rosalind Franlin
crystallographer
double helix

 Max Delbruck         molecular biology

Max Delbruck        
molecular biology

Max Planck

Max Planck Quantum Physics

 

 

 

We then stepped back from classical (descriptive) physiology, with the endless complexity, to molecular biology.  This led us to the genetic code, with a double helix model.  It has recently been found insufficiently explanatory, with the recent construction of triplex and quadruplex models. They have a potential to account for unaccounted for building blocks, such as inosine, and we don’t know whether more than one model holds validity under different conditions .  The other major field of development has been simply unaccounted for in the study of proteomics, especially in protein-protein interactions, and in the energetics of protein conformation, first called to our attention by the work of Jacob, Monod, and Changeux (See Footnote 2).  Proteins are not just rigid structures stamped out by the monotonously simple DNA to RNA to protein concept.  Nothing is ever quite so simple. Just as there are epigenetic events, there are posttranslational events, and yet more.

JPChangeux-150x170

JP Changeux

 

 

 

 

 

 

 

 

The Emergence of Molecular Biology

I now return the discussion to the topic of medicine, the emergence of molecular biology and the need for convergence with biochemistry in the mid-20th century. Jose Eduardo de Salles Roselino recalls “I was previously allowed to make of the conformational energy as made by R Marcus in his Nobel lecture revised (J. of Electroanalytical  Chemistry 438:(1997) p251-259. (See Footnote 1) His description of the energetic coordinates of a landscape of a chemical reaction is only a two-dimensional cut of what in fact is a volcano crater (in three dimensions) (each one varies but the sum of the two is constant. Solvational+vibrational=100% in ordinate) nuclear coordinates in abcissa. In case we could represent it by research methods that allow us to discriminate in one by one degree of different pairs of energy, we would most likely have 360 other similar representations of the same phenomenon. The real representation would take into account all those 360 representations together. In case our methodology was not that fine, for instance it discriminates only differences of minimal 10 degrees in 360 possible, will have 36 partial representations of something that to be perfectly represented will require all 36 being taken together. Can you reconcile it with ATGC?  Yet, when complete genome sequences were presented they were described as though we will know everything about this living being. The most important problems in biology will be viewed by limited vision always and the awareness of this limited is something we should acknowledge and teach it. Therefore, our knowledge is made up of partial representations. If we had the entire genome data for the most intricate biological problems, they are still not amenable to this level of reductionism. But going from general views of signals andsymptoms we could get to the most detailed molecular view and in this case genome provides an anchor.”

“Warburg Effect” describes the preference of glycolysis and lactic acid fermentation rather than oxidative phosphorylation for energy production in cancer cells. Mitochondrial metabolism is an important and necessary component in the functioning and maintenance of the cell, and accumulating evidence suggests that dysfunction of mitochondrial metabolism plays a role in cancer. Progress has demonstrated the mechanisms of the mitochondrial metabolism-to-glycolysis switch in cancer development and how to target this metabolic switch.

 

 

Glycolysis

glycolysis

 

Otto Heinrich Warburg (1883- )

Otto Warburg

435px-Louis_Pasteur,_foto_av_Félix_Nadar_Crisco_edit

Louis Pasteur

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The expression “Pasteur effect” was coined by Warburg when inspired by Pasteur’s findings in yeast cells, when he investigated this metabolic observation (Pasteur effect) in cancer cells. In yeast cells, Pasteur had found that the velocity of sugar used was greatly reduced in presence of oxygen. Not to be confused, in the “Crabtree effect”, the velocity of sugar metabolism was greatly increased, a reversal, when yeast cells were transferred from the aerobic to an anaerobic condition. Thus, the velocity of sugar metabolism of yeast cells was shown to be under metabolic regulatory control in response to change in environmental oxygen conditions in growth. Warburg had to verify whether cancer cells and tissue related normal mammalian cells also have a similar control mechanism. He found that this control was also found in normal cells studied, but was absent in cancer cells. Strikingly, cancer cells continue to have higher anaerobic gycolysis despite the presence of oxygen in their culture media (See Footnote 3).

Taking this a step further, food is digested and supplied to cells In vertebrates mainly in the form of glucose, which is metabolized producing Adenosine Triphosphate (ATP) by two pathways. Glycolysis, occurs via anaerobic metabolism in the cytoplasm, and is of major significance for making ATP quickly, but in a minuscule amount (2 molecules).  In the presence of oxygen, the breakdown process continues in the mitochondria via the Krebs’s cycle coupled with oxidative phosphorylation, which is more efficient for ATP production (36 molecules). Cancer cells seem to depend on glycolysis. In the 1920s, Otto Warburg first proposed that cancer cells show increased levels of glucose consumption and lactate fermentation even in the presence of ample oxygen (known as “Warburg Effect”). Based on this theory, oxidative phosphorylation switches to glycolysis which promotes the proliferation of cancer cells. Many studies have demonstrated glycolysis as the main metabolic pathway in cancer cells.

Albert Szent Gyogy (Warburg’s student) and Otto Meyerhof both studied striated skeletal muscle metabolism invertebrates, and they found those changes observed in yeast by Pasteur. The description of the anaerobic pathway was largely credited to Emden and Meyerhof. Whenever there is increase in muscle work, energy need is above what can be provided by blood supply, the cell metabolism changes from aerobic (where  Acetyl CoA  provides the chemical energy for aerobic production of ATP) to anaerobic metabolism of glucose. In this condition, glucose is obtained directly from its muscle glycogen stores (not from hepatic glycogenolysis).  This is the sole source of chemical energy that is independent of oxygen supplied to the cell. It is a physiological change on muscle metabolism that favors autonomy. It does not depend upon the blood oxygen for aerobic metabolim or blood sources of carbon metabolites borne out from adipose tissue (free fatty acids) or muscle proteins (branched chain amino acids), or vascular delivery of glucose. On that condition, the muscle can perform contraction by its internal source of ATP and uses conversion of pyruvate to lactate in order to regenerate much-needed NAD (by hydride transfer from pyruvate) as a replacement for this mitochondrial function. This regulatory change, keeps glycolysis going at fast rate in order to meet ATP needs of the cell under low yield condition (only two or three ATP for each glucose converted into two lactate molecules). Therefore, it cannot last for long periods of time. This regulatory metabolic change is made in seconds, minutes and therefore happens with the proteins that are already presented in the cell. It does not requires the effect of transcription factors and/or changes in gene expression (See Footnote 1, 2).

In other types mammalian cells, like those from the lens of the eye (86% gycolysis + pentose shunt),  and red blood cells (RBC)[both lacking mitochondria], and also in the deep medullary layer of the kidneys, for lack of mitochondria in the first two cases and normally reduced blood perfusion in the third – A condition required for the counter current mechanism and our ability to concentrate urine also have, permanent higher anaerobic metabolism. In the case of RBC, it includes the ability to produce in a shunt of glycolytic pathway 2,3 diphospho- glycerate that is required to place the hemogloblin macromolecule in an unstable equilibrium between its two forms (R and T – Here presented as simplified accordingly to the model of Monod, Wyman and Changeux. The final model would be even much complex (see for instance, H-W and K review Nature 2007 vol 450: p 964-972 )

Any tissue under a condition of ischemia that is required for some medical procedures (open heart surgery, organ transplants, etc) displays this fast regulatory mechanism (See Footnote 1, 2). A display of these regulatory metabolic changes can be seen in: Cardioplegia: the protection of the myocardium during open heart surgery: a review. D. J. Hearse J. Physiol., Paris, 1980, 76, 751-756 (Fig 1).  The following points are made:

1-       It is a fast regulatory response. Therefore, no genetic mechanism can be taken into account.

2-       It moves from a reversible to an irreversible condition, while the cells are still alive. Death can be seen at the bottom end of the arrow. Therefore, it cannot be reconciled with some of the molecular biology assumptions:

A-       The gene and genes reside inside the heart muscle cells but, in order to preserve intact, the source of coded genetic information that the cell reads and transcribes, DNA must be kept to a minimal of chemical reactivity.

B-       In case sequence determines conformation, activity and function , elevated potassium blood levels could not cause cardiac arrest.

In comparison with those conditions here presented, cancer cells keep the two metabolic options for glucose metabolism at the same time. These cells can use glucose that our body provides to them or adopt temporarily, an independent metabolic form without the usual normal requirement of oxygen (one or another form for ATP generation).  ATP generation is here, an over-simplification of the metabolic status since the carbon flow for building blocks must also be considered and in this case oxidative metabolism of glucose in cancer cells may be viewed as a rich source of organic molecules or building blocks that dividing cells always need.

JES Roselino has conjectured that “most of the Krebs cycle reaction works as ideal reversible thermodynamic systems that can supply any organic molecule that by its absence could prevent cell duplication.” In the vision of Warburg, cancer cells have a defect in Pasteur-effect metabolic control. In case it was functioning normally, it will indicate which metabolic form of glucose metabolism is adequate for each condition. What more? Cancer cells lack differentiated cell function. Any role for transcription factors must be considered as the role of factors that led to the stable phenotypic change of cancer cells. The failure of Pasteur effect must be searched for among the fast regulatory mechanisms that aren’t dependent on gene expression (See Footnote 3).

Extending the thoughts of JES Roselino (Hepatology 1992;16: 1055-1060), reduced blood flow caused by increased hydrostatic pressure in extrahepatic cholestasis decreases mitochondrial function (quoted in Hepatology) and as part of Pasteur effect normal response, increased glycolysis in partial and/or functional anaerobiosis and therefore blocks the gluconeogenic activity of hepatocytes that requires inhibited glycolysis. In this case, a clear energetic link can be perceived between the reduced energetic supply and the ability to perform differentiated hepatic function (gluconeogenesis). In cancer cells, the action of transcription factors that can be viewed as different ensembles of kaleidoscopic pieces (with changing activities as cell conditions change) are clearly linked to the new stable phenotype. In relation to extrahepatic cholestasis mentioned above it must be reckoned that in case a persistent chronic condition is studied a secondary cirrhosis is installed as an example of persistent stable condition, difficult to be reversed and without the requirement for a genetic mutation. (See Footnote 4).

 The Rejection of Complexity

Most of our reasoning about genes was derived from scientific work in microorganisms. These works have provided great advances in biochemistry.

250px-DNA_labeled DNA diagram showing base pairing

double helix

 

hgp_hubris_220x288_72 genome cartoon

Dna triplex pic

Triple helix

 

formation of a triplex DNA structure

formation of triple helix

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1-      The “Gelehrter idea”: No matter what you are doing you will always be better off, in case you have a gene (In chapter 7 Principles of Medical Genetics Gelehrter and Collins Williams & Wilkins 1990).

2-      The idea that everything could be found following one gene one enzyme relationship that works fine for our understanding of the metabolism, in all biological problems.

3-      The idea that everything that explains biochemistry in microorganisms explains also for every living being (J Nirenberg).

4-      The idea that biochemistry may not require that time should be also taken into account. Time must be considered only for genetic and biological evolution studies (S Luria. In Life- The unfinished experiment 1977 C Scribner´s sons NY).

5-      Finally, the idea that everything in biology, could be found in the genome. Since all information in biology goes from DNA through RNA to proteins. Alternatively, are in the DNA, in case the strict line that includes RNA is not included.

This last point can be accepted in case it is considered that ALL GENETIC information is in our DNA. Genetics as part of life and not as its total expression.

For example, when our body is informed that the ambient temperature is too low or alternatively is too high, our body is receiving an information that arrives from our environment. This external information will affect our proteins and eventually, in case of longer periods in a new condition will cause adaptive response that may include conformational changes in transcription factors (proteins) that will also, produce new readings on the DNA. However, it is an information that moves from outside, to proteins and not from DNA to proteins. The last pathway, when transcription factors change its conformation and change DNA reading will follow the dogmatic view as an adaptive response (See Footnotes 1-3).

However, in case, time is taken into account, the first reactions against cold or warmer temperatures will be the ones that happen through change in protein conformation, activities and function before any change in gene expression can be noticed at protein level. These fast changes, in seconds, minutes cannot be explained by changes in gene expression and are strongly linked to what is needed for the maintenance of life.

“It is possible”, says Roselino, “desirable, to explain all these fast biochemical responses to changes in a living being condition as the sound foundation of medical practices without a single mention to DNA. In case a failure in any mechanism necessary to life is found to be genetic in its origin, the genome in context with with this huge set of transcription factors must be taken into account. This is the biochemical line of reasoning that I have learned with Houssay and Leloir. It would be an honor to see it restored in modern terms.”

More on the Mechanism of Metabolic Control

It was important that genomics would play such a large role in medical research for the last 70 years. There is also good reason to rethink the objections of the Nobelists James Watson and Randy Schekman in the past year, whatever discomfort it brings.  Molecular biology has become a tautology, and as a result deranged scientific rigor inside biology.

Crick & Watson with their DNA model, 1953

Eatson and Crick

Randy-Schekman Berkeley

Randy-Schekman Berkeley

 

 

According to JES Roselino, “consider that glycolysis is oscillatory thanks to the kinetic behavior of Phosphofructokinase. Further, by its effect upon Pyruvate kinase through Fructose 1,6 diphosphate oscillatory levels, the inhibition of gluconeogenesis is also oscillatory. When the carbon flow through glycolysis is led to a maximal level gluconeogenesis will be almost completely blocked. The reversal of the Pyruvate kinase step in liver requires two enzymes (Pyruvate carboxylase (maintenance of oxaloacetic levels) + phosphoenolpyruvate carboxykinase (E.C. 4.1.1.32)) and energy requiring reactions that most likely could not as an ensemble, have a fast enough response against pyruvate kinase short period of inhibition during high frequency oscillatory periods of glycolytic flow. Only when glycolysis oscillates at low frequency the opposite reaction could enable gluconeogenic carbon flow.”

In case it can be shown in a rather convincing way, the same reasoning could be applied to understand how simple replicative signals inducing Go to G1 transition in cells, could easily overcome more complex signals required for cell differentiation and differentiated function.

Perhaps the problem of overextension of the equivalence of the DNA and what happens to the organism is also related to the initial reliance on a single cell model to relieve the complexity (which isn’t fully the case).

For instance, consider this fragment:
“Until only recently it was assumed that all proteins take on a clearly defined three-dimensional structure – i.e. they fold in order to be able to assume these functions.”
Cold Spring Harbour Symp. Quant. Biol. 1973  p 187-193 J.C Seidel and J Gergely – Investigation of conformational changes in Spin-Labeled Myosin Model for muscle contraction:
Huxley, A. F. 1971 Proc. Roy. Soc (London) (B) 178:1
Huxley, A.F and R. M. Simmons,1971. Nature 233:633
J.C Haselgrove X ray Evidence for a conformational Change in the Actin-containing filaments…Cold Spring Harbour Symp Quant Biol.1972 v 37: p 341-352

Only a very small sample indicating otherwise. Proteins were held as interacting macromolecules, changing their conformation in regulatory response to changes in the microenvironment (See Footnote 2). DNA was the opposite, non-interacting macromolecules to be as stable as a library must be.

The dogma held that the property of proteins could be read in DNA alone. Consequenly, the few examples quoted above, must be ignored and all people must believe that DNA alone, without environmental factors roles, controls protein amino acid sequence (OK), conformation (not true), activity (not true) and function (not true).

It appeared naively to be correct from the dogma to conclude from interpreting your genome: You have a 50% increased risk of developing the following disease (deterministic statement).  The correct form must be: You belong to a population that has a 50% increase in the risk of….followed by –  what you must do to avoid increase in your personal risk and the care you should take in case you want to have longer healthy life.  Thus, genetics and non-genetic diseases were treated as the same and medical foundations were reinforced by magical considerations (dogmas) in a very profitable way for those involved besides the patient.

 Footnotes:

  1. There is a link of electricity with ions in biology and the oscillatory behavior of some electrical discharges.  In addition, the oscillatory form of electrical discharged may have allowed Planck to relate high energy content with higher frequencies and conversely, low energy content in low frequency oscillatory events.  One may think of high density as an indication of great amount of matter inside a volume in space.  This helps the understanding of Planck’s idea as a high-density-energy in time for a high frequency phenomenon.
  1. Take into account a protein that may have its conformation restricted by an S-S bridge. This protein also, may move to another more flexible conformation in case it is in HS HS condition when the S-S bridge is broken. Consider also that, it takes some time for a protein to move from one conformation for instance, the restricted conformation (S-S) to other conformations. Also, it takes a few seconds or minutes to return to the S-S conformation (This is the Daniel Koshland´s concept of induced fit and relaxation time used by him in order to explain allosteric behavior of monomeric proteins- Monod, Wyman and Changeux requires tetramer or at least, dimer proteins).
  1. In case you have glycolysis oscillating in a frequency much higher than the relaxation time you could lead to the prevalence of high NADH effect leading to high HS /HS condition and at low glycolytic frequency, you could have predominance of S-S condition affecting protein conformation. In case you have predominance of NAD effect upon protein S-S you would get the opposite results.  The enormous effort to display the effect of citrate and over Phosphofructokinase conformation was made by others. Take into account that ATP action as an inhibitor in this case, is a rather unusual one. It is a substrate of the reaction, and together with its action as activator  F1,6 P (or its equivalent F2,6 P) is also unusual. However, it explains oscillatory behaviour of glycolysis. (Goldhammer , A.R, and Paradies: PFK structure and function, Curr. Top Cell Reg 1979; 15:109-141).
  1. The results presented in our Hepatology work must be viewed in the following way: In case the hepatic (oxygenated) blood flow is preserved, the bile secretory cells of liver receive well-oxygenated blood flow (the arterial branches bath secretory cells while the branches originated from portal vein irrigate the hepatocytes.  During extra hepatic cholestasis the low pressure, portal blood flow is reduced and the hepatocytes do not receive enough oxygen required to produce ATP that gluconeogenesis demands. Hepatic artery do not replace this flow since, its branches only join portal blood fluxes after the previous artery pressure  is reduced to a low pressure venous blood – at the point where the formation of hepatic vein is. Otherwise, the flow in the portal vein would be reversed or, from liver to the intestine. It is of no help to take into account possible valves for this reasoning since minimal arterial pressure is well above maximal venous pressure and this difference would keep this valve in permanent close condition. In low portal blood flow condition, the hepatocyte increases pyruvate kinase activity and with increased pyruvate kinase activity Gluconeogenesis is forbidden (See Walsh & Cooper revision quoted in the Hepatology as ref 23). For the hemodynamic considerations, role of artery and veins in hepatic portal system see references 44 and 45 Rappaport and Schneiderman and Rappapaport.

 

 Appendix I.

metabolic pathways

metabolic pathways

Signals Upstream and Targets Downstream of Lin28 in the Lin28 Pathway

Signals Upstream and Targets Downstream of Lin28 in the Lin28 Pathway

 

 

 

 

 

 

 

 

1.  Functional Proteomics Adds to Our Understanding

Ben Schuler’s research group from the Institute of Biochemistry of the University of Zurich has now established that an increase in temperature leads to folded proteins collapsing and becoming smaller. Other environmental factors can trigger the same effect. The crowded environments inside cells lead to the proteins shrinking. As these proteins interact with other molecules in the body and bring other proteins together, understanding of these processes is essential “as they play a major role in many processes in our body, for instance in the onset of cancer”, comments study coordinator Ben Schuler.

Measurements using the “molecular ruler”

“The fact that unfolded proteins shrink at higher temperatures is an indication that cell water does indeed play an important role as to the spatial organisation eventually adopted by the molecules”, comments Schuler with regard to the impact of temperature on protein structure. For their studies the biophysicists use what is known as single-molecule spectroscopy. Small colour probes in the protein enable the observation of changes with an accuracy of more than one millionth of a millimetre. With this “molecular yardstick” it is possible to measure how molecular forces impact protein structure.

With computer simulations the researchers have mimicked the behaviour of disordered proteins. They want to use them in future for more accurate predictions of their properties and functions.

Correcting test tube results

That’s why it’s important, according to Schuler, to monitor the proteins not only in the test tube but also in the organism. “This takes into account the fact that it is very crowded on the molecular level in our body as enormous numbers of biomolecules are crammed into a very small space in our cells”, says Schuler. The biochemists have mimicked this “molecular crowding” and observed that in this environment disordered proteins shrink, too.

Given these results many experiments may have to be revisited as the spatial organisation of the molecules in the organism could differ considerably from that in the test tube according to the biochemist from the University of Zurich. “We have, therefore, developed a theoretical analytical method to predict the effects of molecular crowding.” In a next step the researchers plan to apply these findings to measurements taken directly in living cells.

Explore further: Designer proteins provide new information about the body’s signal processesMore information: Andrea Soranno, Iwo Koenig, Madeleine B. Borgia, Hagen Hofmann, Franziska Zosel, Daniel Nettels, and Benjamin Schuler. Single-molecule spectroscopy reveals polymer effects of disordered proteins in crowded environments. PNAS, March 2014. DOI: 10.1073/pnas.1322611111

 

Effects of Hypoxia on Metabolic Flux

  1. Glucose-6-phosphate dehydrogenase regulation in the hepatopancreas of the anoxia-tolerantmarinemollusc, Littorina littorea

JL Lama , RAV Bell and KB Storey

Glucose-6-phosphate dehydrogenase (G6PDH) gates flux through the pentose phosphate pathway and is key to cellular antioxidant defense due to its role in producing NADPH. Good antioxidant defenses are crucial for anoxia-tolerant organisms that experience wide variations in oxygen availability. The marine mollusc, Littorina littorea, is an intertidal snail that experiences daily bouts of anoxia/hypoxia with the tide cycle and shows multiple metabolic and enzymatic adaptations that support anaerobiosis. This study investigated the kinetic, physical and regulatory properties of G6PDH from hepatopancreas of L. littorea to determine if the enzyme is differentially regulated in response to anoxia, thereby providing altered pentose phosphate pathway functionality under oxygen stress conditions.

Several kinetic properties of G6PDH differed significantly between aerobic and 24 h anoxic conditions; compared with the aerobic state, anoxic G6PDH (assayed at pH 8) showed a 38% decrease in K G6P and enhanced inhibition by urea, whereas in pH 6 assays Km NADP and maximal activity changed significantly.

All these data indicated that the aerobic and anoxic forms of G6PDH were the high and low phosphate forms, respectively, and that phosphorylation state was modulated in response to selected endogenous protein kinases (PKA or PKG) and protein phosphatases (PP1 or PP2C). Anoxia-induced changes in the phosphorylation state of G6PDH may facilitate sustained or increased production of NADPH to enhance antioxidant defense during long term anaerobiosis and/or during the transition back to aerobic conditions when the reintroduction of oxygen causes a rapid increase in oxidative stress.

Lama et al.  Peer J 2013.   http://dx.doi.org/10.7717/peerj.21

 

  1. Structural Basis for Isoform-Selective Inhibition in Nitric Oxide Synthase

    TL. Poulos and H Li

In the cardiovascular system, the important signaling molecule nitric oxide synthase (NOS) converts L-arginine into L-citrulline and releases nitric oxide (NO). NO produced by endothelial NOS (eNOS) relaxes smooth muscle which controls vascular tone and blood pressure. Neuronal NOS (nNOS) produces NO in the brain, where it influences a variety of neural functions such as neural transmitter release. NO can also support the immune system, serving as a cytotoxic agent during infections. Even with all of these important functions, NO is a free radical and, when overproduced, it can cause tissue damage. This mechanism can operate in many neurodegenerative diseases, and as a result the development of drugs targeting nNOS is a desirable therapeutic goal.

However, the active sites of all three human isoforms are very similar, and designing inhibitors specific for nNOS is a challenging problem. It is critically important, for example, not to inhibit eNOS owing to its central role in controlling blood pressure. In this Account, we summarize our efforts in collaboration with Rick Silverman at Northwestern University to develop drug candidates that specifically target NOS using crystallography, computational chemistry, and organic synthesis. As a result, we have developed aminopyridine compounds that are 3800-fold more selective for nNOS than eNOS, some of which show excellent neuroprotective effects in animal models. Our group has solved approximately 130 NOS-inhibitor crystal structures which have provided the structural basis for our design efforts. Initial crystal structures of nNOS and eNOS bound to selective dipeptide inhibitors showed that a single amino acid difference (Asp in nNOS and Asn in eNOS) results in much tighter binding to nNOS. The NOS active site is open and rigid, which produces few large structural changes when inhibitors bind. However, we have found that relatively small changes in the active site and inhibitor chirality can account for large differences in isoform-selectivity. For example, we expected that the aminopyridine group on our inhibitors would form a hydrogen bond with a conserved Glu inside the NOS active site. Instead, in one group of inhibitors, the aminopyridine group extends outside of the active site where it interacts with a heme propionate. For this orientation to occur, a conserved Tyr side chain must swing out of the way. This unanticipated observation taught us about the importance of inhibitor chirality and active site dynamics. We also successfully used computational methods to gain insights into the contribution of the state of protonation of the inhibitors to their selectivity. Employing the lessons learned from the aminopyridine inhibitors, the Silverman lab designed and synthesized symmetric double-headed inhibitors with an aminopyridine at each end, taking advantage of their ability to make contacts both inside and outside of the active site. Crystal structures provided yet another unexpected surprise. Two of the double-headed inhibitor molecules bound to each enzyme subunit, and one molecule participated in the generation of a novel Zn site that required some side chains to adopt alternate conformations. Therefore, in addition to achieving our specific goal, the development of nNOS selective compounds, we have learned how subtle differences in and structure can control proteinligand interactions and often in unexpected ways.

 

300px-Nitric_Oxide_Synthase

Nitric oxide synthase

arginine-NO-citulline cycle

arginine-NO-citulline cycle

active site of eNOS (PDB_1P6L) and nNOS (PDB_1P6H).

active site of eNOS (PDB_1P6L) and nNOS (PDB_1P6H).

 

 

NO - muscle, vasculature, mitochondria

NO – muscle, vasculature, mitochondria

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure:  (A) Structure of one of the early dipeptide lead compounds, 1, that exhibits excellentisoform selectivity. (B, C) show the crystal structures of the dipeptide inhibitor 1 in the active site of eNOS (PDB: 1P6L) and nNOS (PDB: 1P6H). In nNOS, the inhibitor “curls” which enables the inhibitor R-amino group to interact with both Glu592 and Asp597. In eNOS, Asn368 is the homologue to nNOS Asp597.

Accounts in Chem Res 2013; 46(2): 390-98.

  1. Jamming a Protein Signal

Interfering with a single cancer-promoting protein and its receptor can open this resistance mechanism by initiating autophagy of the affected cells,  according to researchers at The University of Texas MD Anderson Cancer Center  in the journal Cell Reports.  According to Dr. Anil Sood and Yunfei Wen, lead and first authors, blocking  prolactin, a potent growth factor for ovarian cancer, sets off downstream events that result in cell by autophagy, the process  recycles damaged organelles and proteins for new use by the cell through the phagolysozome. This in turn, provides a clinical rationale for blocking prolactin and its receptor to initiate sustained autophagy as an alternative strategy for treating cancers.

Steep reductions in tumor weight

Prolactin (PRL) is a hormone previously implicated in ovarian, endometrial and other cancer development andprogression. When PRL binds to its cell membrane receptor, PRLR, activation of cancer-promoting cell signaling pathways follows.  A variant of normal prolactin called G129R blocks the reaction between prolactin and its receptor. Sood and colleagues treated mice that had two different lines of human ovarian cancer, both expressing the prolactin receptor, with G129R. Tumor weights fell by 50 percent for mice with either type of ovarian cancer after 28 days of treatment with G129R, and adding the taxane-based chemotherapy agent paclitaxel cut tumor weight by 90 percent. They surmise that higher doses of G129R may result in even greater therapeutic benefit.

 

3D experiments show death by autophagy

 

[video width=”1280″ height=”720″ mp4=”http://pharmaceuticalintelligence.com/wp-content/uploads/2014/04/1741-7007-11-65-s1-macromolecular-juggling-by-ubiquitylation-enzymes1.mp4″][/video]

 

Next the team used the prolactin-mimicking peptide to treat cultures of cancer spheroids which sharply reduced their numbers, and blocked the activation of JAK2 and STAT signaling pathways.

Protein analysis of the treated spheroids showed increased presence of autophagy factors and genomic analysis revealed increased expression of a number of genes involved in autophagy progression and cell death.  Then a series of experiments using fluorescence and electron microscopy showed that the cytosol of treated cells had large numbers of cavities caused by autophagy.

The team also connected the G129R-induced autophagy to the activity of PEA-15, a known cancer inhibitor. Analysis of tumor samples from 32 ovarian cancer patients showed that tumors express higher levels of the prolactin receptor and lower levels of phosphorylated PEA-15 than normal ovarian tissue. However, patients with low levels of the prolactin receptor and higher PEA-15 had longer overall survival than those with high PRLR and low PEA-15.

Source: MD Anderson Cancer Center

 

  1. Chemists’ Work with Small Peptide Chains of Enzymes

Korendovych and his team designed seven simple peptides, each containing seven amino acids. They then allowed the molecules of each peptide to self-assemble, or spontaneously clump together, to form amyloids. (Zinc, a metal with catalytic properties, was introduced to speed up the reaction.) What they found was that four of the seven peptides catalyzed the hydrolysis of molecules known as esters, compounds that react with water to produce water and acids—a feat not uncommon among certain enzymes.

“It was the first time that a peptide this small self-assembled to produce an enzyme-like catalyst,” says Korendovych. “Each enzyme has to be an exact fit for its respective substrate,” he says, referring to the molecule with which an enzyme reacts. “Even after millions of years, nature is still testing all the possible combinations of enzymes to determine which ones can catalyze metabolic reactions. Our results make an argument for the design of self-assembling nanostructured catalysts.”

Source: Syracuse University

Here are three articles emphasizing the value of combinatorial analysis, which can be formed from genomic, clinical, and proteomic data sets.

 

  1. Comparative analysis of differential network modularity in tissue specific normal and cancer protein interaction networks

    F Islam , M Hoque , RS Banik , S Roy , SS Sumi, et al.

As most biological networks show modular properties, the analysis of differential modularity between normal and cancer protein interaction networks can be a good way to understand cancer more significantly. Two aspects of biological network modularity e.g. detection of molecular complexes (potential modules or clusters) and identification of crucial nodes forming the overlapping modules have been considered in this regard.

The computational analysis of previously published protein interaction networks (PINs) has been conducted to identify the molecular complexes and crucial nodes of the networks. Protein molecules involved in ten major cancer signal transduction pathways were used to construct the networks based on expression data of five tissues e.g. bone, breast, colon, kidney and liver in both normal and cancer conditions.

Cancer PINs show higher level of clustering (formation of molecular complexes) than the normal ones. In contrast, lower level modular overlapping is found in cancer PINs than the normal ones. Thus a proposition can be made regarding the formation of some giant nodes in the cancer networks with very high degree and resulting in reduced overlapping among the network modules though the predicted molecular complex numbers are higher in cancer conditions.

Islam et al. Journal of Clinical Bioinformatics 2013, 3:19-32

  1. A new 12-gene diagnostic biomarker signature of melanoma revealed by integrated microarray analysis

    Wanting Liu , Yonghong Peng and Desmond J. Tobin
    PeerJ 1:e49;        http://dx.doi.org/10.7717/peerj.49

Here we present an integrated microarray analysis framework, based on a genome-wide relative significance (GWRS) and genome-wide global significance (GWGS) model. When applied to five microarray datasets on melanoma published between 2000 and 2011, this method revealed a new signature of 200 genes. When these were linked to so-called ‘melanoma driver’ genes involved in MAPK, Ca2+, and WNT signaling pathways we were able to produce a new 12-gene diagnostic biomarker signature for melanoma (i.e., EGFR, FGFR2, FGFR3, IL8, PTPRF, TNC, CXCL13, COL11A1, CHP2, SHC4, PPP2R2C, andWNT4).We have begun to experimentally validate a subset of these genes involved inMAPK signaling at the protein level, including CXCL13, COL11A1, PTPRF and SHC4 and found these to be overexpressed inmetastatic and primarymelanoma cells in vitro and in situ compared to melanocytes cultured from healthy skin epidermis and normal healthy human skin.

 

catalytic amyloid forming particle

catalytic amyloid forming particle

 

 

 

 

 

 

 

        8.    PanelomiX: A threshold-based algorithm to create panels of biomarkers

X Robin , N Turck , A Hainard , N Tiberti, et al.
               Translational Proteomics 2013.    http://dx.doi.org/10.1016/j.trprot.2013.04.003

The PanelomiX toolbox combines biomarkers and evaluates the performance of panels to classify patients better than singlemarkers or other classifiers. The ICBTalgorithm proved to be an efficient classifier, the results of which can easily be interpreted.

Here are two current examples of the immense role played by signaling pathways in carcinogenic mechanisms and in treatment targeting, which is also confounded by acquired resistance.

 

  1. Triple-Negative Breast Cancer

  1. epidermal growth factor receptor (EGFR or ErbB1) and
  2. high activity of the phosphatidylinositol 3-kinase (PI3K)–Akt pathway

are both targeted in triple-negative breast cancer (TNBC).

  • activation of another EGFR family member [human epidermal growth factor receptor 3 (HER3) (or ErbB3)] may limit the antitumor effects of these drugs.

This study found that TNBC cell lines cultured with the EGFR or HER3 ligand EGF or heregulin, respectively, and treated with either an Akt inhibitor (GDC-0068) or a PI3K inhibitor (GDC-0941) had increased abundance and phosphorylation of HER3.

The phosphorylation of HER3 and EGFR in response to these treatments

  1. was reduced by the addition of a dual EGFR and HER3 inhibitor (MEHD7945A).
  2. MEHD7945A also decreased the phosphorylation (and activation) of EGFR and HER3 and
  3. the phosphorylation of downstream targets that occurred in response to the combination of EGFR ligands and PI3K-Akt pathway inhibitors.

In culture, inhibition of the PI3K-Akt pathway combined with either MEHD7945A or knockdown of HER3

  1. decreased cell proliferation compared with inhibition of the PI3K-Akt pathway alone.
  2. Combining either GDC-0068 or GDC-0941 with MEHD7945A inhibited the growth of xenografts derived from TNBC cell lines or from TNBC patient tumors, and
  3. this combination treatment was also more effective than combining either GDC-0068 or GDC-0941 with cetuximab, an EGFR-targeted antibody.
  4. After therapy with EGFR-targeted antibodies, some patients had residual tumors with increased HER3 abundance and EGFR/HER3 dimerization (an activating interaction).

Thus, we propose that concomitant blockade of EGFR, HER3, and the PI3K-Akt pathway in TNBC should be investigated in the clinical setting.

Reference: Antagonism of EGFR and HER3 Enhances the Response to Inhibitors of the PI3K-Akt Pathway in Triple-Negative Breast Cancer. JJ Tao, P Castel, N Radosevic-Robin, M Elkabets, et al.  Sci. Signal., 25 March 2014;
7(318), p. ra29   http://dx.doi.org/10.1126/scisignal.2005125

 

                  10.   Metastasis in RAS Mutant or Inhibitor-Resistant Melanoma Cells

The protein kinase BRAF is mutated in about 40% of melanomas, and BRAF inhibitors improve progression-free and overall survival in these patients. However, after a relatively short period of disease control, most patients develop resistance because of reactivation of the RAF–ERK (extracellular signal–regulated kinase) pathway, mediated in many cases by mutations in RAS. We found that BRAF inhibition induces invasion and metastasis in RAS mutant melanoma cells through a mechanism mediated by the reactivation of the MEK (mitogen-activated protein kinase kinase)–ERK pathway.

Reference: BRAF Inhibitors Induce Metastasis in RAS Mutant or Inhibitor-Resistant Melanoma Cells by Reactivating MEK and ERK Signaling. B Sanchez-Laorden, A Viros, MR Girotti, M Pedersen, G Saturno, et al., Sci. Signal., 25 March 2014;  7(318), p. ra30  http://dx.doi.org/10.1126/scisignal.2004815

Appendix II.

The world of physics in the twentieth century saw the end of determinism established by Newton. This is characterized by discrete laws that describe natural observations. These are in gravity and in eletricity. In an early phase of investigation, an era of galvanic or voltaic electricity represented a revolutionary break from the historical focus on frictional electricity. Alessandro Voltadiscovered that chemical reactions could be used to create positively charged anodes and negatively charged cathodes.  In 1790, Prof. Luigi Alyisio Galvani of Bologna, while conducting experiments on “animal electricity“, noticed the twitching of a frog’s legs in the presence of an electric machine. He observed that a frog’s muscle, suspended on an iron balustrade by a copper hook passing through its dorsal column, underwent lively convulsions without any extraneous cause, the electric machine being at this time absent.  Volta communicated a description of his pile to the Royal Society of London and shortly thereafter Nicholson and Cavendish (1780) produced the decomposition of water by means of the electric current, using Volta’s pile as the source of electromotive force.

Siméon Denis Poisson attacked the difficult problem of induced magnetization, and his results provided  a first approximation. His innovation required the application of mathematics to physics.  His memoirs on the theory of electricity and magnetism created a new branch of mathematical physics.  The discovery of electromagnetic induction was made almost simultaneously and independently by Michael Faraday and Joseph Henry. Michael Faraday, the successor of Humphry Davy, began his epoch-making research relating to electric and electromagnetic induction in 1831. In his investigations of the peculiar manner in which iron filings arrange themselves on a cardboard or glass in proximity to the poles of a magnet, Faraday conceived the idea of magnetic “lines of force” extending from pole to pole of the magnet and along which the filings tend to place themselves. On the discovery being made that magnetic effects accompany the passage of an electric current in a wire, it was also assumed that similar magnetic lines of force whirled around the wire. He also posited that iron, nickel, cobalt, manganese, chromium, etc., are paramagnetic (attracted by magnetism), whilst other substances, such as bismuth, phosphorus, antimony, zinc, etc., are repelled by magnetism or are diamagnetic.

Around the mid-19th century, Fleeming Jenkin‘s work on ‘ Electricity and Magnetism ‘ and Clerk Maxwell’s ‘ Treatise on Electricity and Magnetism ‘ were published. About 1850 Kirchhoff published his laws relating to branched or divided circuits. He also showed mathematically that according to the then prevailing electrodynamic theory, electricity would be propagated along a perfectly conducting wire with the velocity of light. Herman Helmholtz investigated the effects of induction on the strength of a current and deduced mathematical equations, which experiment confirmed. In 1853 Sir William Thomson (later Lord Kelvin) predicted as a result of mathematical calculations the oscillatory nature of the electric discharge of a condenser circuit.  Joseph Henry, in 1842 discerned  the oscillatory nature of the Leyden jardischarge.

In 1864 James Clerk Maxwell announced his electromagnetic theory of light, which was perhaps the greatest single step in the world’s knowledge of electricity. Maxwell had studied and commented on the field of electricity and magnetism as early as 1855/6 when On Faraday’s lines of force was read to the Cambridge Philosophical Society. The paper presented a simplified model of Faraday’s work, and how the two phenomena were related. He reduced all of the current knowledge into a linked set of differential equations with 20 equations in 20 variables. This work was later published as On Physical Lines of Force in1861. In order to determine the force which is acting on any part of the machine we must find its momentum, and then calculate the rate at which this momentum is being changed. This rate of change will give us the force. The method of calculation which it is necessary to employ was first given by Lagrange, and afterwards developed, with some modifications, by Hamilton’s equations. Now Maxwell logically showed how these methods of calculation could be applied to the electro-magnetic field. The energy of a dynamical systemis partly kinetic, partly potential. Maxwell supposes that the magnetic energy of the field is kinetic energy, the electric energy potential.  Around 1862, while lecturing at King’s College, Maxwell calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light.   Maxwell’s electromagnetic theory of light obviously involved the existence of electric waves in free space, and his followers set themselves the task of experimentally demonstrating the truth of the theory. By 1871, he presented the Remarks on the mathematical classification of physical quantities.

A Wave-Particle Dilemma at the Century End

In 1896 J.J. Thomson performed experiments indicating that cathode rays really were particles, found an accurate value for their charge-to-mass ratio e/m, and found that e/m was independent of cathode material. He made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called “corpuscles”, had perhaps one thousandth of the mass of the least massive ion known (hydrogen). He further showed that the negatively charged particles produced by radioactive materials, by heated materials, and by illuminated materials, were universal.  In the late 19th century, the Michelson–Morley experiment was performed by Albert Michelson and Edward Morley at what is now Case Western Reserve University. It is generally considered to be the evidence against the theory of a luminiferous aether. The experiment has also been referred to as “the kicking-off point for the theoretical aspects of the Second Scientific Revolution.” Primarily for this work, Albert Michelson was awarded theNobel Prize in 1907.

Wave–particle duality is a theory that proposes that all matter exhibits the properties of not only particles, which have mass, but also waves, which transfer energy. A central concept of quantum mechanics, this duality addresses the inability of classical concepts like “particle” and “wave” to fully describe the behavior of quantum-scale objects. Standard interpretations of quantum mechanics explain this paradox as a fundamental property of the universe, while alternative interpretations explain the duality as an emergent, second-order consequence of various limitations of the observer. This treatment focuses on explaining the behavior from the perspective of the widely used Copenhagen interpretation, in which wave–particle duality serves as one aspect of the concept of complementarity, that one can view phenomena in one way or in another, but not both simultaneously.  Through the work of Max PlanckAlbert EinsteinLouis de BroglieArthur Compton, Niels Bohr, and many others, current scientific theory holds that all particles also have a wave nature (and vice versa).

Beginning in 1670 and progressing over three decades, Isaac Newton argued that the perfectly straight lines of reflection demonstrated light’s particle nature, but Newton’s contemporaries Robert Hooke and Christiaan Huygens—and later Augustin-Jean Fresnel—mathematically refined the wave viewpoint, showing that if light traveled at different speeds in different, refraction could be easily explained. The resulting Huygens–Fresnel principle was supported by Thomas Young‘s discovery of double-slit interference, the beginning of the end for the particle light camp.  The final blow against corpuscular theory came when James Clerk Maxwell discovered that he could combine four simple equations, along with a slight modification to describe self-propagating waves of oscillating electric and magnetic fields. When the propagation speed of these electromagnetic waves was calculated, the speed of light fell out. While the 19th century had seen the success of the wave theory at describing light, it had also witnessed the rise of the atomic theory at describing matter.

Matter and Light

In 1789, Antoine Lavoisier secured chemistry by introducing rigor and precision into his laboratory techniques. By discovering diatomic gases, Avogadro completed the basic atomic theory, allowing the correct molecular formulae of most known compounds—as well as the correct weights of atoms—to be deduced and categorized in a consistent manner. The final stroke in classical atomic theory came when Dimitri Mendeleev saw an order in recurring chemical properties, and created a table presenting the elements in unprecedented order and symmetry.   Chemistry was now an atomic science.

Black-body radiation, the emission of electromagnetic energy due to an object’s heat, could not be explained from classical arguments alone. The equipartition theorem of classical mechanics, the basis of all classical thermodynamic theories, stated that an object’s energy is partitioned equally among the object’s vibrational modes. This worked well when describing thermal objects, whose vibrational modes were defined as the speeds of their constituent atoms, and the speed distribution derived from egalitarian partitioning of these vibrational modes closely matched experimental results. Speeds much higher than the average speed were suppressed by the fact that kinetic energy is quadratic—doubling the speed requires four times the energy—thus the number of atoms occupying high energy modes (high speeds) quickly drops off. Since light was known to be waves of electromagnetism, physicists hoped to describe this emission via classical laws. This became known as the black body problem. The Rayleigh–Jeans law which, while correctly predicting the intensity of long wavelength emissions, predicted infinite total energy as the intensity diverges to infinity for short wavelengths.

The solution arrived in 1900 when Max Planck hypothesized that the frequency of light emitted by the black body depended on the frequency of the oscillator that emitted it, and the energy of these oscillators increased linearly with frequency (according to his constant h, where E = hν). By demanding that high-frequency light must be emitted by an oscillator of equal frequency, and further requiring that this oscillator occupy higher energy than one of a lesser frequency, Planck avoided any catastrophe; giving an equal partition to high-frequency oscillators produced successively fewer oscillators and less emitted light. And as in the Maxwell–Boltzmann distribution, the low-frequency, low-energy oscillators were suppressed by the onslaught of thermal jiggling from higher energy oscillators, which necessarily increased their energy and frequency. Planck had intentionally created an atomic theory of the black body, but had unintentionally generated an atomic theory of light, where the black body never generates quanta of light at a given frequency with energy less than .

In 1905 Albert Einstein took Planck’s black body model in itself and saw a wonderful solution to another outstanding problem of the day: the photoelectric effect, the phenomenon where electrons are emitted from atoms when they absorb energy from light.   Only by increasing the frequency of the light, and thus increasing the energy of the photons, can one eject electrons with higher energy. Thus, using Planck’s constant h to determine the energy of the photons based upon their frequency, the energy of ejected electrons should also increase linearly with frequency; the gradient of the line being Planck’s constant. These results were not confirmed until 1915, when Robert Andrews Millikan, produced experimental results in perfect accord with Einstein’s predictions. While  the energy of ejected electrons reflected Planck’s constant, the existence of photons was not explicitly proven until the discovery of the photon antibunching effect  When Einstein received his Nobel Prizein 1921, it was  for the photoelectric effect, the suggestion of quantized light. Einstein’s “light quanta” represented the quintessential example of wave–particle duality. Electromagnetic radiation propagates following  linear wave equations, but can only be emitted or absorbed as discrete elements, thus acting as a wave and a particle simultaneously.

Radioactivity Changes the Scientific Landscape

The turn of the century also features radioactivity, which later came to the forefront of the activities of World War II, the Manhattan Project, the discovery of the chain reaction, and later – Hiroshima and Nagasaki.

Marie Curie

Marie Curie

 

 

 

Marie Skłodowska-Curie was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first woman to win a Nobel Prize, the only woman to win in two fields, and the only person to win in multiple sciences. She was also the first woman to become a professor at the University of Paris, and in 1995 became the first woman to be entombed on her own merits in the Panthéon in Paris. She shared the 1903 Nobel Prize in Physics with her husband Pierre Curie and with physicist Henri Becquerel. She won the 1911 Nobel Prize in Chemistry.  Her achievements included a theory of radioactivity (a term that she coined, techniques for isolating radioactive isotopes, and the discovery of polonium and radium. She named the first chemical element that she discovered – polonium, which she first isolated in 1898 – after her native country. Under her direction, the world’s first studies were conducted into the treatment of neoplasms using radioactive isotopes. She founded the Curie Institutes in Paris and in Warsaw, which remain major centres of medical research today. During World War I, she established the first military field radiological centres.  Curie died in 1934 due to aplastic anemia brought on by exposure to radiation – mainly, it seems, during her World War I service in mobile X-ray units created by her.

 

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