CHAPTER IX 



FERMENTS, OR ENZYMES 



One of the most striking developments of modern research in biochem- 

 istry concerns the nature of enzyme action. So remarkable are many of 

 the facts that have been brought to light that it can not fail to interest 

 every one engaged in the study of life phenomena whatever the nature 

 of that study may be to know something of the main questions at 

 present occupying the attention of investigators in this field. In this 

 chapter a brief survey will be given of some of these questions; no at- 

 tempt will be made at completeness, and only where necessary for the 

 sake of example will reference be made to individual types of enzyme 

 action. 



The discovery by Buchner that an enzyme can be expressed from yeast 

 cells which is capable of instantly bringing about the alcoholic fermen- 

 tation of dextrose solutions has been responsible for a great deal of the 

 modern advance. Formerly, yeast cells were believed to bring about 

 alcoholic fermentation as a result of their growth: it was believed to be 

 a life phenomenon, or " vital process." Now we know that yeast cells 

 produce an intracellular ferment or endo-enzyme* to which its sucroclastic 

 properties are due and which can act apart from the cells that produce it. 

 It is no great stretch of imagination to think of all chemical reactions 

 mediated by cellular activity as due to a similar mechanism, and this thought 

 has led to the hypothesis that all processes of intermediary metabolism in 

 the animal and plant are caused by enzyme action. Before Buchner 's 

 day we knew only of the extracellular enzymes (such, for example, as 

 the digestive ferments), that is to say, of enzymes, produced indeed by 

 cells, but secreted from them and acting outside their protoplasm; now 

 we must recognize intracellular enzymes acting where they are produced, 

 in the protoplasm of the cell. But we must not permit this conception to 

 carry us too far. Without further investigation we must not imagine 

 that the riddle of life is thus solved. 



As an example of the role which extra- and intracellular enzymes are 

 supposed to play in the animal economy may be cited the metabolism of 

 protein. Proteolytic enzymes are very widely distributed in the active 

 tissues of the animal and plant. By their agency in animal life, the com- 



*The terms "ferment" and "enzyme" arc synonymous, but the latter is preferable as the noun, 

 leaving the former to be used as the verb. 



71 



