A textbook of biochemistry for students of medicine and science / by A.T. Cameron.

  • Alexander Thomas Cameron
Date:
1931
Catalogue details

Licence: In copyright

Credit: A textbook of biochemistry for students of medicine and science / by A.T. Cameron. Source: Wellcome Collection.

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    which breaks down into one product of the decomposition of the substrate, and a compound of enzyme and a second product of this decomposition ; this decomposes less readily, and since the bound enzyme is inactive, such a theory accounts in part for the apparent loss of an enzyme during a reaction. If the substrate S is broken down into A and B by the action of the enzyme E then the suggested changes may he represented : E + S zif. E—S A + E—B A + B + E. The marked specificity exhibited by the majority of enzymes is associated, not with individual compounds, but with special types of linkages present in a series of com¬ pounds. This association has led to the so-called lock cmcl key conception of enzyme action. Reversibility of Enzyme Action. It has already been stated that the reverse action induced by some enzymes leads to production of precisely those compounds that such an enzyme usually hydrolyses, as with lipase and ethyl buty¬ rate. More frequently a reverse action will take place when an enzyme is added to a concentrated solution of the hydro¬ lysed products of its own action, but the compound built up is not quite the same as the one originally hydrolysed. Thus if a protein is hydrolysed by pepsin, and then more pepsin added to the concentrated products, a protein, termed a plastein, is built up, very similar to the original, but less soluble. Purification of Enzymes. The technique of purification varies for different enzymes. Except in eases in which the enzyme is contained in some special secretion (such as the gastric and pancreatic juices) the structure of the containing cells must be destroyed. To this end methods such as Buchner’s can be used, and the expressed cell juice obtained, or the cells can be killed and allowed to decompose (by autolysis ; see Chapter XX.), the resulting products being- dried at low temperature and the enzymes extracted by
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