Amino acid

“ One of the great differences between animal protein and plant protein is that the percentages of the different amino acids are very different. Some of the amino acids that make up a large proportion of animal protein are very scantily represented in plant protein. To make human protein we must not only have all the amino acid ingredients, but we must also have enough of every one. On a purely vegetarian diet to get enough of those amino acids which are scantily present in plants we have to eat a large surplus of those amino acids which are specially abundant. ”

“ Protein is about the most complex substance that we know anything about; it is made up of a number of organic acids combined chemically. These organic acids all contain nitrogen, which puts them into a class to which is given the name of amino acids. To the chemist the name amino acid shows a certain kind of chemical formation; to us it need mean no more than an organic acid which contains nitrogen. The proteins which are in our bodies are as complex as any that exist and some of them are made up of as many as eighteen different amino acids. ”

“ The remaining material is supposed to be also composed of amino-acids which are linked together in some arrangement which is not broken apart by any method of hydrolysis which has yet been devised. This view is borne out by the fact that substances which exhibit all the characteristic properties of proteins have been artificially synthetized, by using only amino-acid compounds. Animal proteins often show a much larger proportion of unhydrolyzable material than do plant proteins. ”

“ Among the products of protein decomposition are amino acids. A determination of amino acid nitrogen was taken as a measure of decomposition–the more of the amino acid nitrogen present the greater the amount of decomposition. This being true, the following table, summarized from Tressler's results, will show the superiority of dry salt over strong brine for preserving fish. ”

“ In the case we have just cited—that is, the four-amino-acid protein with two amino acids of one type and two of another—the formula is:
Of course, the factorials involved in calculating the number of amino acid combinations in hemoglobin are larger. We must start with factorial 539—the total number of amino acids in hemoglobin—and divide that by the product of factorial 75, factorial 54, factorial 50 and so on—the number of each amino acid present.
The factorials of the lower integers are easy enough to calculate (see Figure 8) . Unfortunately they build up rather rapidly. ”

“ 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. ”

“ Plant proteins, in general, usually contain larger proportions of proline and of glutamic acid than are found in animal proteins; also more arginine than is found in any of the animal proteins except the protamines, which contain as high as 85 per cent of this amino-acid.
Of the twenty-five plant proteins which have thus far been hydrolyzed and studied from this standpoint, all contained leucine, proline, phenylalanine, aspartic acid, glutamic acid, tyrosine, histidine, and arginine; two gave no glycine; two others, no alanine; four contained no lysine; and one, no tryptophane. ”

“ 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. ”

“ As to the differentiation of the dissolved skin substance into albumoses, peptones, monamino acids, diamino acids, ammonia, etc., a modification of Stiasny’s method38 for the examination of soaks and old limes may be used.
The method is based on the fact, discovered by Schiff, that formaldehyde reacts with amino acids, forming methylen-amino acids, which are distinctly acid and allow a sharp titration with phenolphthalein as indicator, while the amino acids themselves react almost neutral. ”

“ There are virtually an infinite number of different proteins but all are composed of the same few dozen amino acids hooked together in highly variable patterns. Amino acids themselves are highly complex organic molecules too. The human body custom-assembles all its proteins from amino acids derived from digesting protein foods, and can also manufacture small quantities of certain of its own amino acids to order, but there are eight amino acids it cannot make and these are for that reason called essential amino acids. Essential amino acids must be contained in the food we eat. ”

“ If, however, it is true that in normal digestion the protein molecule is completely broken down into relatively simple fragments, non-protein in nature, i. e., into amino-acids and polypeptides, and that from these fragments specific proteins are reconstructed, then it is plain that animals fed on a diet free from protein, but with a proper amount of these nitrogenous cleavage products, should live and thrive, assuming, of course, a sufficient addition of non-nitrogenous food. ”

“ When we eat lean beef or pork we get exactly the same eighteen amino acids that are in our own proteins, but not put together in precisely the same way. What we have to do with these proteins is to break them up into the amino acids of which they are composed and then put these together again in the combination which makes up human protein. ”

“ About twenty different amino-acids have been isolated from the products of hydrolysis of natural proteins, and this number is being added to from time to time, as the methods of isolation and identification of these compounds are improved. Many of these same amino-acids have been found in free form in plant tissues, particularly in rapidly growing buds, or shoots, or in germinating seeds, where they undoubtedly exist as intermediate products in the transformation of proteins into other types of compounds. ”

“ A study of the results of the hydrolysis of some twenty common plant proteins has shown that it is rarely possible to recover the amino-acids in sufficient quantities to account for a full 100 per cent of the material used, the actual percentage of amino-acids recovered usually totaling from 60 to 80 per cent. ”

“ The Simple Proteins Albumins—soluble in water and dilute salt solutions, coagulated by heat. Globulins—insoluble in water, soluble in dilute salt solutions, coagulated by heat. Glutelins—insoluble in water or dilute salt solutions, soluble in dilute acids or alkalies, coagulated by heat. Prolamins—insoluble in water, etc., soluble in 80 per cent alcohol. Histones—soluble in water, insoluble in ammonia, not coagulated by heat. Protamines—soluble in water and ammonia, not coagulated by heat, yielding large proportions of diamino-acids on hydrolysis. ”

“ A minute study of the subject by Osborne, Mendel and numerous other physiologic chemists have shown that a perfect protein is composed of more than a dozen different bodies called amino-acids, each of which must be present in the right proportion to enable the body to use the protein in body building. Each plant produces its one peculiar kind of protein. The protein of milk, caseine, is a perfect protein. ”

“ We can well imagine that in the life and death of tissue cells autolytic decompositions are constantly taking place whereby cell protein is broken down into its component parts, while at the same time a synthesis of protein may be occurring from other amino-acids brought by blood or lymph with a possible utilization of some of the fragments liberated by the autolysis. In other words, our conception of nutritional changes to-day embodies the hypothesis of a synthesis of protein throughout the body ”

“ The building stones of the body are the amino-acids. All proteins contain them, but the kinds and proportions are not always the same. It has been shown by biologic experiments that life and growth cannot be maintained when certain amino-acids are deficient. ”

“ The condensation of amino-acids into proteins, or the reverse decomposition, is very readily accomplished in all living protoplasm, under the influence of special protein-attacking enzymes, which are almost universally present in the cytoplasm. ”

“ A second thing to be mentioned about growth is a discovery which has attracted a great deal of attention of late years; we will realize of course that the chief thing in the making of new protoplasm is the building together of protein out of amino acids. It is evident that for the manufacture of new protein all the eighteen amino acids must be present in sufficient proportion to give enough of each. ”

“ Flesh foods necessarily furnish complete proteins. The proteins of milk and eggs are also complete proteins. The proteins met in the vegetable world are exceedingly varied in character. Each species of plant produces its own kind of proteins. Vegetable proteins differ greatly among themselves. Complete proteins are comparatively rare. The proteins of cereals, for example, have been shown to be deficient in some of the essential amino acids. ”

“ Apparently the intestinal secretion contains no trace of a ferment acting on native protein, but a ferment-erepsin—is present in fair amount in the intestinal mucous membrane and in small amount in the secretion, which acts in an alkaline medium on proteoses, peptones, and on casein, converting them into crystalline products of the nature of amino acids. ”

“ I puckered my eyes at the mouth-filling term Kennedy smiled. “It would mean,” he explained, “a great quantity of the amino-acids, non-coagulable, nitrogenous compounds in the blood. You know the indols, the phenols, and the amins are produced both by putrefactive bacteria and by the process of metabolism, the burning up of the tissues in the process of utilizing the energy that means life. ”

“ The amino acids that are circulating in the blood stream after every meal are primarily to be used for repairing protoplasmic wastage; also they serve for the manufacture of new protoplasm, provided growth is going on. In theory an adult who is through with all his growth except in the skin and one or two other minor tissues should be able to get along with just the amount of protein which will make good his protoplasmic wastage. ”

“ To be sure, hemoglobin has somewhat more than four amino acids in its molecule so the number of possible arrangements is to be expected to be somewhat more than twenty-four. Still, proteins are so important that biochemists would be willing to go to an unusual amount of effort to solve the problem of their structure and the mere presence of additional arrangements might not discourage them. Trial and error might be a little more tedious than in the case of heme, but, given time enough, it ought to be as sure as death and taxes. ”

“ This experiment proves that the action of the dung is a complex one, due to the combined action of enzymes and chemical compounds upon the skin. These compounds, which are principally amines, and salts of amino-acids, probably assist the enzymes, and at the same time act upon the lime remaining in the skin from the previous liming process. Whether a skin, which has never been submitted to the liming operation, could be bated by enzymes alone, without the addition of amines, has not, so far as I know, been tried, but it is highly probable that this would be the case. ”

“ The dark bars represent the counts of all sites that fall into each class while the light bars represent the number of sites estimated to be under strong constraint via the bootstrap procedure. The dashed line indicates what the count of total unpreferred conserved codons would have been had unpreferred 4D sites been conserved to the same extent as preferred 4D sites in otherwise conserved amino acids, i.e. the dashed line represents the proportion of U:P in all conserved amino acids. ”

“ 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. ”

“ And seeing that the whole progress of modern investigation is in favour of the doctrine of continuity, it is a fair and probable speculation — though only a speculation — that, as there are some plants which can manufacture protein out of such apparently intractable mineral matters as carbonic acid, water, nitrate of ammonia, and metallic salts; while others need to be supplied with their carbon and nitrogen in the somewhat less raw form of tartrate of ammonia and allied compounds ”

“ The presence of protein in the plasma-membrane of, sea-urchin eggs is also indicated by the fact that the cytolytic action of acids may be lessened or counteracted by neutral salts like sodium or calcium chloride. Such antagonistic actions between acids and salts, while not shown by colloids in general, are peculiarly characteristic of certain proteins. Thus the rate of swelling of gelatine (a typical scleroprotein) in water is greatly increased by the addition of a little acid ”