Enzyme

“ So far as is known, the peculiar substances called enzymes are produced only by the living cells of animals and plants, although there are certain inorganic substances that so closely reproduce the essential qualities of enzyme action that they might almost be termed 'inorganic enzymes.' The enzymes obtained from the animal or plant cell have never been isolated in a pure condition, and hence no definite knowledge of their chemical composition and constitution has yet been secured. ”

“ The list of enzymes grows longer almost daily, as some new one is separated having a specific action, until one is almost led to believe that the mechanism of life itself, as manifested in the cell, is due to enzymes.
It has been found that enzymes act very much in the same way as inorganic catalysers. As an example, the velocity of the reaction of invertase (the enzyme of yeast which hydrolyses cane sugar to grape sugar) has been compared with the same hydrolysis brought about by heating a solution of cane sugar with a mineral acid. ”

“ Nothing is known with certainty concerning the chemical nature of enzymes. Being colloidal in nature, they adsorb carbohydrates, proteins, fats, etc., so that active enzyme preparations often respond to the characteristic tests for these groups of substances ”

“ Many poisons and chemical disinfectants (Chapter XIV) which kill living organisms will also stop the action of enzymes, though generally more of the substance is required, so that it is possible to destroy the living cells by such means and yet the action of the enzyme will continue.
(e) Most enzymes have an optimum reaction of medium either acid, alkaline or neutral, depending on the particular enzyme, though some few seem to act equally well within a considerable range on either side of the neutral point. ”

“ Any given enzyme affects only a single reaction; or at most acts only upon a single group of compounds which have similar molecular configuration. Usually it is only a single compound whose decomposition is accelerated by the action of a particular enzyme; but there are a few enzymes, such as maltase (which acts on all α-glucosides) and emulsin (which acts on all β-glucosides) which act catalytically upon groups of considerable numbers of similar compounds.
Enzymes, like all other catalysts, act more energetically at increased temperatures ”

“ While there is a great variety of enzymes which may be produced by a single individual organism, the same enzyme may be found in the greatest variety of organisms; as, for example, the protease trypsin, which has been found in several species of bacteria, in the carnivorous plant known as "Venus' Fly Trap," and in the human pancreas, as well as that of all other animals. ”

“ Now there are certain facts regarding the action of mineral acids upon sugars and proteids, of various salts upon the phenomena of clotting and oxidation and of other changes brought about by inorganic substances which render it difficult to set enzyme action apart as a' thing by itself. The action of an enzyme is essentially 'catalytic,' that is, it is able to exert an influence wholly out of proportion to its quantity, and itself remain unaltered at the end of the process. ”

“ In considering the mechanism by which enzymes act, it must be remembered in the first place that they are colloids, and, as such, will form absorption compounds with the substrate, or body, upon which they are acting. It is difficult to understand how an enzyme can exert an action on the substrate, unless it enters into some kind of combination with it, although this may be only a temporary one. The action of some enzymes has been found to be due to extremely small amounts of certain metals, e.g. ”

“ Analyses of enzymatic activity involved in catechins galloylated and hydrolysis biosynthesis in different organs and leaves at different developmental stages.The enzyme activity unit was defined as the amount of product formed by one milligram of enzyme catalyzed in one minute (μg min−1 mg−1 protein) ”

“ The whole field of enzyme study is therefore at present beset with the same sort of difficulties that the science of bacteriology encountered before the days of 'pure cultures,' and it is doubtless true that effects that are at the present time ascribed to individual enzymes are in reality caused by mixtures of distinct varieties. ”

“ All enzymes are "killed" by boiling the solutions in which they are contained. Dry preparations of enzyme material can withstand somewhat higher temperatures, for somewhat longer periods of time, than can the same enzyme in moist condition or in solution. [Pg 185] When an enzyme has once been inactivated by heating, or "killed," it can never be restored to activity again. ”

“ This reaction, which had for so long been looked upon as a typical illustration of the power of life in inducing chemical change, is merely a simple process of enzymolysis. The yeast plant, it is true, produces the enzyme; but the isolated ferment, once formed, is just as capable of decomposing the sugar as the yeast plant itself. Indeed, the latter is able to accomplish this chemical reaction, solely because of the presence of the enzyme or ferment, now called zymase. In all forms of animal and vegetable tissue, intra- and extra-cellular enzymes abound ”

“ When the juice from well-washed yeast is incubated, the phenomenon of autofermentation is observed. The juice contains an abundant supply of enzyme, co-enzyme, and phosphate or hexosephosphate, and in this case the controlling factor is usually the supply of sugar, which is conditioned by the concentration of the diastatic enzyme or of the complex carbohydrates as the case may be. When this is the case the measured rate of fermentation is the rate at which sugar is being produced in the juice, this being the slowest of the various reactions which are proceeding under these circumstances. ”

“ 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. ”

“ The above list includes only the more common and best-known plant enzymes. It seems reasonable to suppose that for every individual type of organic compound which may occur in general plant groups, or even in single species, there is a corresponding enzyme available to affect its physiological alterations. Indeed, new preparations of active enzymes from special types of plants and new evidences of the existence of enzymes in various plant organisms are continuously being reported. ”

“ The enzymes themselves are not used up in the process, so if time enough is allowed, a very small amount of enzyme can bring about the decomposition of a very large amount of material. In our bodies the whole digestive process consists of a succession of decompositions of complex materials into simpler ones under the speeding-up influence of enzymes. We have a number of different kinds of foodstuffs to be decomposed and a corresponding number of enzymes. ”

“ Lipase was one of the first enzymes in which the reversibility of the reaction was shown, i.e. it is not only capable of hydrolysing a fat, but also of causing the formation of one by the combination of the fatty acid and glycerin.107 This explains why the reaction of such an enzyme is never complete. An equilibrium is reached just as with ordinary reversible chemical reactions like the precipitation of magnesium hydroxide by ammonia. ”

“ Tissue Enzymes.—The important part played by enzymes in the digestion of the food has suggested other uses for them in the body. It has been recently shown that many of the chemical changes in the tissues are in all probability due to the presence of enzymes. An illustration of what a tissue enzyme may do is seen in the changes which fat undergoes. In order for the body to use up its reserve fat, it must be transferred from the connective tissue cells, where it is stored, to the cells of the active tissues where it is to be used. ”

“ If the fermenting power of the juice is to be preserved by repeated regeneration for a long period, it is absolutely necessary to add the co-enzyme solution each time as soon as fermentation has ceased, since the enzyme in the absence of this addition rapidly disappears, even in the presence of sugar. ”

“ The difference between the α- and β-forms is best shown by the selective action of enzymes. Fischer found that maltase, an enzyme occurring in yeast cells, hydrolysed α-glucosides but not the β; while emulsin, an enzyme occurring in bitter almonds, hydrolyses the β but not the α. ”

“ Our conception of the processes involved in proteid katabolism is that of a series of progressive chemical decompositions, in which intracellular enzymes play the all-important part. The intermediary products formed are definite bodies because of the specific nature of the active enzymes, and, secondly, because of the chemical nature of the substances acted upon. In other words, oxidation in the animal body takes the shape of a series of well-defined chemical reactions, in which chemical constitution and specific enzyme action are the predetermining cause. ”

“ Incidentally, their behaviour towards enzymes has been studied, and the remarkable selective action of these ferments on the various groups, due apparently to differences of configuration, has been established, with the result that much light has been thrown on the mechanism of enzyme action and on the general theory of fermentation. ”

“ Very much too little is known, by even the scientific physician of to-day, regarding the action of drugs on the enzymes of the body. Some chemicals when present with the enzyme increase its power to do work; others decrease its power; and others stop it entirely. The concentration of the chemicals is of paramount importance. Most chemicals in concentrated solutions entirely prevent the action of ferments. ”

“ More recently it has been intimated that the acridity may be due to some ferment or enzyme, which has been derived in part from the self-decomposition of protoplasm and in part by the process of oxidation and reduction. ”

“ It has been pointed out that the influence of an enzyme or indeed any catalytic agent is simply to retard or accelerate changes which ordinarily take place more slowly or more rapidly. In other words, an enzyme simply influences the rate of change, not the final condition of the substance upon which it acts. The nature of the change, the final state of chemical equilibrium, is determined by the chemical forces within the substance itself, the speed at which the change occurs is determined by the enzyme. ”

“ The fatty matters and soaps in the skin are acted upon by the lipolytic enzymes, and the fats to some extent emulsified, so that they may be easily removed from the skin by scudding or pressing.
It must be clearly understood that enzyme action alone is not sufficient, as has been previously explained, but that the dung enzymes, acting in conjunction with the chemical compounds present, produce the specific puering effect. ”

“ The organism, which is performing this process all the time, or after every meal, does it in a different way, without special heating and without the acid. A soluble ferment, a diastase or enzyme, serves as the oxidizing agent to produce the same result. Looking at the beginning and the end, the two operations are the same. The special agent gives up none of its substance. It withdraws after having accomplished its work, and not a trace of it is left. Here, in the mechanism of the action of these soluble ferments, resides the mystery, still complete, of vital chemistry. ”

“ The principle enunciated by Armstrong, that in the synthetic action of hydrolytic enzymes not the original compound but an isomer is formed which can not be hydrolyzed by the enzyme, may possibly be of great importance in the understanding of life phenomena. ”

“ Since the number of different reactions which take place within a living cell is very great, and since these chemical changes are extremely variable in type, it follows that the number of different enzymes which must exist in either a plant or an animal organism is likewise very large. For example, fourteen different enzymes have been isolated from the digestive system, and at least sixteen from the liver, of animals. They are universally present in living protoplasm of every kind, from the most minute bacterium to the largest forest trees, in the plant kingdom ”

“ For example, if the enzyme were furnished with a mixture of 5 parts of A and 1 part of C, it would make strands containing, on the average, 25 sequences of AAA, 5 of AAC, 5 of ACA, 5 of CAA, and 1 each of ACC, CAC, and CCA. The proportion of triplets within the strands of a polynucleotide is reflected in the proportion of amino acids in polypeptides that are obtained in the cell-free system. Most of the present knowledge of the amino acid code is based on this concept. ”

“ The gene responsible for producing the needed enzyme has been cloned and its structure in normal individuals and Gaucher's disease patients is being studied. Scientists are continuing to refine techniques for replacing the missing enzyme as a useful form of therapy. ”