ENZYMES AND THEIR ACTION 183 



in producing different changes in the same substance by different 

 enzymes. 



The name " enzyme " comes from Greek words meaning 

 " in yeast," as the nature and effect of the enzyme involved in the 

 alcoholic fermentation of sugars by yeast were those which were 

 first recognized and understood. It was at first thought, by Pas- 

 teur and his students, that fermentation is the direct result of the 

 life activities of the yeast plant. Later, it was found that water 

 extracts from sprouted barley, from almond seeds, and from the 

 stomach, pancreas, etc., were able to bring about the decompo- 

 sition of starch, of amygdalin, and of proteins, respectively, in a 

 way which seemed to be quite comparable to the fermentative 

 action of yeasts. Hence, it was thought that there were two 

 varieties of active agents of this kind, one composed of living cells 

 and the other non-living chemical compounds, and these were 

 called the "organized ferments" and the " unorganized ferments," 

 respectively. However, in 1897, Biichner found that by grinding 

 yeast cells with sharp sand .until they were completely disinte- 

 grated and then submitting the mass to hydraulic pressure, he 

 could obtain a clear liquid, entirely free from living cells, which was 

 just as active in producing fermentation as was the yeast itself. 

 This discovery paved the way for a long series of investigations, 

 which have conclusively demonstrated that there is no distinction 

 between " organized " and " unorganized " ferments, that all 

 living organisms perform their characteristic functions by means 

 of the enzymes which they contain, and that these enzymes can 

 bring about their characteristic catalytic effects outside the cell, 

 or tissue which elaborates them, just as well as within it, provided 

 only that the conditions of temperature, acidity or alkalinity of 

 the medium, etc., are suitable for the particular enzyme action 

 which is under consideration, 



GENERAL PROPERTIES OF ENZYMES 



Since enzymes are catalysts, it is plain that an accurate de- 

 scription of their activity should, in each case, refer to the influ- 

 ence which they exert upon some definite reaction velocity. But 

 since the phrases necessary to describe such an effect are cumber- 

 some and inconvenient, and since most of the reactions which are 

 accelerated by the catalytic action of enzymes are either simple 



