ENZYME ACTION 39 



free from yeast. The clear fluid, which he called zymase, ex- 

 tracted in this manner from the living yeast, was thus shown to 

 be the active agent in alcoholic fermentation. Such agents in 

 chemical activities are called ferments or enzymes (from Greek 

 en, in, and zyme, yeast). Still later investigations have shown 

 that a second enzyme, called co-enzyme and also produced by 

 the yeast cell, is necessary to activate the zymase. 



Enzymes in Vital Activities. The zymase and its co-enzyme, 

 which can thus be extracted from the protoplasm of yeast, 

 are normal products of the vital or metabolic activities of the 

 organism and are examples of the many analogous ferments 

 which yeast is capable of producing. Macfadyen, Morris, and 

 Rowland as well as other investigators, have devised methods 

 of cutting up minute organisms in mass, thus breaking down 

 the cells more perfectly than had been done before. In this 

 way it has been possible to isolate from yeast not only a powerful 

 zymase but other enzymes as well, including maltase, invertase, 

 endotryptase, rennin, and traces of two others, all of which 

 must be present in the protoplasm of normal yeast cells. 



One of the characteristics of the chemical activities in proto- 

 plasm which distinguishes them from similar activities in 

 physical nature is the speed with which they take place. Thus 

 sugar dissolved in water and exposed to the air oxidizes very 

 slowly. There is no difference in kind between this process 

 and the oxidation of sugar in the living cell, but there is a great 

 difference in speed. Such differences in the rapidity of chem- 

 ical actions in living and lifeless matter are due, as we now 

 know, to the presence of innumerable enzymes in all kinds of 

 living cells. The first hint of these elusive agents in vital 

 activities was given as early as 1836 by Berzelius when he dis- 

 covered the action due to what he called "catalytic force." 

 Subsequent researches have shown that his catalyzers, which 

 we now know as enzymes, are chemical substances which par- 

 ticipate in chemical reactions by forming compounds of unstable 

 and intermediate character. The compounds break down 

 easily, thus freeing the enzymes and enabling them to repeat the 

 process, so that they appear to be unaltered by the reactions 



