Peptide

“ Bioinformatics analysis For the proteome, only peptides with TMT reporter ion signal intensities for all ten samples were used for further bioinformatics analysis. Any duplicate peptides were removed before the data was SumScale normalised. The two normalised data files were then merged together to give one 10vs10 file comparison. Any peptides which did not have intensity values in all twenty TMT reporter ion channels were filtered out and median values were taken of the control and treated samples respectively. A total of 1906 peptides were quantified across all liver samples. ”

“ The latter are further reduced to still simpler products, and eventually amino-acids are left, which again may be subjected to further reductions.
It could, further, be easily shown that the cells of the body are able to decompose into their structural units the so-called polypeptides, that is, amino-acids linked in the manner of acid amides. These ferments have acquired the name of peptolytic ferments. Their presence has been demonstrated in animals and plants inside the most varied kinds of cells. In plants they are not always found in an active state. ”

“ The first experiments were made with dogs and rabbits. White of egg, or horse blood-serum, was introduced parenterally into these animals, that is to say, avoiding the intestinal canal; tests were then made to see whether the plasma of the animals under experiment either decomposed certain polypeptides, or whether it decomposed them quicker than the plasma of the same animal did before the injection of the disharmonious substance. The very first experiments gave a positive result. It was found that the contents of the blood increased in peptolytic ferments. ”

“ Pep′tics, digestion considered as a science: the digestive organs; Pep′togen, a substance producing peptone, any preparation that facilitates digestion.—adjs. Peptogen′ic, Peptog′enous, Pepton′ic.—ns. Pep′tōne, one of a class of albumenoids formed by the action of the chemical ferment pepsin and hydrochloric acid, the latter first converting into a syntonin or acid protein, the former converting this syntonin into peptone—they are soluble in water, are not coagulated by boiling, and pass readily through an animal membrane, being therefore easily absorbed ”

“ Pepsin is elaborated in the so-called chief cells of the gastric glands as an inert precursor—propepsin. It is only when it comes into contact with the acid of the juice that it is activated and rendered capable of attacking the protein of the food. ”

“ Absorption of the products of digestion tends to increase the activity of the secreting cells, but we have no tangible proof that any particular kinds of food are directly peptogenous, i.e., that they lead to a storing up in the gastric cells, for example, of pepsinogen, although it may be that the so-called peptogenous foods give rise to a more active conversion of pepsinogen into pepsin.23 As already stated, the zymogen is manufactured directly from the cell-protoplasm, and the constructive power is certainly not directly controlled by the character of the food ingested. ”

“ Enzymes are extremely sensitive to acids, bases, or salts, their activity being often enormously enhanced or, in other cases, entirely inhibited, by the presence in the reacting medium of very small amounts of free acids, or bases, or even of certain neutral salts. For example, pepsin, the enzyme of the stomach will act only in the presence of a slightly acid medium and is wholly inactive in a mixture which contains even the slightest amount of free alkaline material; while trypsin, the similar enzyme of the intestine, acts only under alkaline conditions. ”

“ Stated in different language, it is apparently the purpose of digestion, through the enzymes, pepsin, trypsin and erepsin, to thoroughly dismember the protein molecule so that no vestige of its original structure remains; while out of the many fragments or chemical groups so split apart the body can reconstruct proteins adapted to its own particular needs. This means synthesis of a most marked kind, quite different in character from that implied by the hypothetical transformation of absorbed proteoses and peptone in the mucous membrane of the intestine. ”

“ Furthermore, in considering absorption as it occurs in the living stomach, we must necessarily give due weight to the selective power of the epithelial cells, a power which may be far more potent even than we suppose. Hence, without attempting at this point to draw any broad deductions from our experiments we may simply lay stress upon the facts themselves, viz., that the primary products of pepsin-proteolysis are diffusible, and, like true peptones, are capable of passing through animal and vegetable membranes, although to a less extent. ”

“ In general properties and reactions, pepsin and trypsin may be closely related; both are products of the katabolic action of specific protoplasmic cells, but the inner nature or structure of the two must be quite different. Pepsin, as we have seen, is powerless to produce any change in proteid bodies unless acids are present to lend their aid. Furthermore, pepsin is limited in its action to the production of proteoses and peptones, while trypsin gives rise to a series of hydrolytic cleavages which result in the ultimate formation of comparatively simple bodies. ”

“ In any active pancreatic digestion of either a native proteid, or of the products of pepsin-proteolysis, the anti-group is represented mainly by antipeptone, although there is often found a small amount of a peculiar antialbumid-like body, insoluble in the weak alkaline fluid. ”

“ It is to be remembered, however, that the very nature of the proteid molecule precludes the possibility of anything like a complete decomposition into crystalline or other simple products. Full fifty per cent. of the peptone formed must be antipeptone, which cannot be further changed by trypsin under any circumstances, so that, whether the amount of proteid in the intestine be large or small, or whether it is exposed for a longer or shorter period to trypsin-proteolysis, there will always be a fairly large amount for absorption. ”

“ In considering the general phenomena of proteolysis by trypsin, one is especially impressed by the large and rapid formation of peptone which almost invariably results from the action of a moderately strong solution of the ferment, on nearly every form of proteid matter. To be sure, primary products are first formed, but these are quickly converted into peptone, and a little experience in studying the action of pepsin and trypsin soon reveals the fact that the latter is especially a peptone-forming ferment. ”

“ Dosage: 30 Gm. or 1 ounce (U.S.P.) .
*Pepsinum (Pepsin.) , Pepsin, U.S.P.—Contains a proteolytic ferment or enzyme from the stomach of the hog.
White or yellowish scales, grains, or powder, having a slightly acid or saline taste and no offensive odor. Soluble in water (1:50) ; [Pg 156] nearly insoluble in alcohol. Digests 3000 times its own weight of coagulated egg albumen.
Action and Uses: Used to assist in the gastric digestion of proteins. Usually superfluous, since gastric juice generally contains sufficient pepsin to perform gastric digestion. ”

“ It is very evident from what has been said that all forms of proteid matter, i.e., all the members of the three main groups spoken of in our classification of the proteids, excepting only nuclein, reticulin, and the keratins, are capable of undergoing proteolysis with pepsin-hydrochloric acid. Further, in every case the main products of the transformation are proteoses; viz., albumoses, caseoses, gelatoses, vitelloses, myosinoses, etc., according to the nature of the proteid undergoing proteolysis; true peptones being formed in less abundance. ”

“ The primary and secondary products of pepsin-proteolysis, as well as unaltered proteids, are alike subject to these changes, and bodies of the simplest constitution may result in both cases from the series of hydrolytic changes set in motion by this proteolytic enzyme. The power of the ferment as a contact agent is astonishing, for in the case of trypsin no accessory body is necessary to bring out its latent power. Water, proteid, and the enzyme at the body-temperature are all that is necessary to call forth prompt and energetic hydrolytic action. ”

“ Thus, it was found that when alcohol was added in considerable quantity to a ten per cent. solution of peptone, the stomach-mucosa was greatly reddened, while in two hours the absorption of peptone amounted to 11.8 per cent. But in any event, these results certainly do not favor the view that the products of gastric digestion are absorbed as soon as they are formed. It is, no doubt, quite different in the intestine, but in the stomach, where pepsin-proteolysis occurs, we have, I think, no grounds for assuming that either peptones or proteoses are rapidly absorbed. ”

“ Pepsin, in the presence of hydrochloric acid, acts on proteids, and changes them into proteoses Peptone and proteoses and peptone. Comparatively little food is completely peptonized in gastric digestion. Proteoses are intermediate products between food proteids and peptone, being the principal product of the action of the gastric juice. Thus it is seen that this stomach-action is only preparatory for the digestive processes of the intestines. ”

“ In pepsin-proteolysis we have to deal, in my opinion, with a series of progressive hydrolytic changes in which peptones are the final products of the transformation. Commencing with the formation of acid-albumin or syntonin, hydrolysis and cleavage proceed hand in hand, under the guiding influence of the proteolytic enzyme, and each onward step in the process is marked by the appearance of a new body corresponding to the extent of the hydrolysis ”

“ Now, we understand why proteoses and peptone are not normally present in the circulating blood, even of the portal vein. We see that it is no longer necessary to assume a construction of blood proteins from absorbed proteoses and peptone. The old dictum, so often quoted, that the proteins of our muscle tissue, for example, are simple transformation products of the various food proteins no longer satisfies us, since it is so out of harmony with observed facts. We see opening up before us a totally different conception of the process of digestion so far at least as it relates to protein food. ”

“ Owing to the prominent rôle they play in the human body in connection with digestive processes they have been subjected to exhaustive study. Two chief groups are recognized, the peptic enzymes, of which pepsin, the enzyme of the gastric juice, is the type, and the tryptic enzymes, the best known of which is the trypsin secreted by the mammalian pancreas. ”

“ With relatively large amounts of proteid, we may have half or even quarter saturated proteid molecules, in which the weakness of the combined acid is far more pronounced than in the case of the fully saturated molecule. Such a condition of things must obviously exist in the early stages of gastric digestion. With an excess of proteid matter in the stomach, some time must elapse before the secretion of hydrochloric acid will be sufficient to furnish acid for all of the proteid matter present, yet pepsin-proteolysis does not wait the appearance of free acid. ”

“ In the stomach, the hydrochloric acid helps to make it soften and swell, and then pepsin begins its digestion. Protein, like fat and carbohydrate, can be subdivided into smaller and smaller portions, finally being reduced to a form which the body can absorb, namely, amino acids, of which there may be 17 or 18 kinds from a single protein. ”

“ The reagent is prepared by dissolving 30 grains of flesh peptone, 4 grains of salicylic acid, and 30 minims of strong acetic acid, in sufficient water to produce 8 fluid oz. of solution. Thus prepared, the peptone shows no signs of decomposition on keeping. To use the test, mix 1 fluid drachm of the reagent with 20 minims of urine, previously diluted to a standard specific gravity of 1.003. A haze is produced, which will be found to be more or less distinct, according to the proportion of bile salts present. ”

“ At first there is a marked and rapid progression; the proteid undergoing proteolysis is rapidly dissolved, and both proteoses and peptones may be detected in abundance. But if we continue to watch the changing relations of primary and secondary proteoses and peptones, we find that progression soon ceases to be rapid, and eventually travels onward at a snail’s pace. Thus, in one experiment with coagulated egg-albumin, there was found at the end of forty-eight hours’ digestion with pepsin-hydrochloric acid, only thirty-seven per cent. ”

“ The pepsin, when taken from the press and allowed to become air-dry, is a very tough substance, and presents, according to thickness, a different appearance, resembling in thin sheets parchment paper, and in thick layers sole leather; its colour varies from a dim straw yellow to a brownish yellow. Besides a little mucus, it contains small quantities of phosphate of lime and chloride of sodium, which, however, do not interfere with its digestive properties, as they are found also in normal gastric juice. ”

“ I began taking syrup of pepsin to artificially digest my food and thus take some of the burden off my stomach. A friendly druggist took sufficient interest in me to inform me that there was not enough pepsin in the ordinary digestive syrups and elixirs to digest a mosquito’s dinner. When asked why this ferment was omitted from such preparations, the druggist confided to me in a whisper: “Pepsin is a drug that costs money, while diluted molasses is cheap.” ”