MODE OF ACTION OF ZYMASE 95 



CH 2 OH 



I 

 groups by the action of the zymase CH OH. These groups combine 



COH 



with the protoplasm. The protoplasm will secrete glycogen which 

 will finally be hydrolyzed into glucose by the glycogenase. Two con- 

 ditions are then possible: when the yeast is in the presence of air and 

 when it does not have air at its disposition. 



In the first case, under the influence of oxygenase, put in evidence 

 by Griiss, the molecules of glucose are decomposed into the above 

 grouping which are oxidized by the oxygen liberated by oxygenase 

 and thus changed into carbon dioxide and water. The reaction may 

 be expressed by the following equation: 



CH 2 OH-CHOH-COH + 6O = 3C0 2 + 3H 2 0. 



This is ordinary aerobic respiration. 



In the second case, the enzyme which we have come to know under 

 the name of hydrogenase acts on the products of decomposition from 

 glucose. Owing to the intervention of water, CO 2 will be formed in 

 a first phase with a liberation of hydrogen. In the second phase these 

 hydrogen atoms will be used to unite with the rest of the glucose 

 molecule. 



CH 2 OH-CHOH-COH + 3H 2 O = 3C0 2 + 12H. 



.rnase 



Second 2 (CH 2 OH-CHOH-COH) + 12H = 3C 2 H 5 OH + 3H 2 O. 



JL nase 



This theory of Griiss, in spite of its complexity, has the advan- 

 tage of explaining the role of oxygenase and hydrogenase. 



Another theory has been expounded by Wohl. It has been stated 

 that small quantities of lactic acid are often found among the prod- 

 ucts of alcoholic fermentation. Some, especially Buchner and Mei- 

 senheimer, have regarded this acid as intermediary in the mechanism 

 of the decomposition of glucose into alcohol and carbon dioxide. This 

 may be regarded as taking place in two phases. In the first phase, 

 the zymase transforms the glucose into lactic acid, and in the second, 

 another enzyme, the lactacidase, decomposes the lactic acid into al- 

 cohol and carbon dioxide. However, Buchner and Meisenheimer have 

 not succeeded in transforming lactic acid into alcohol and C0 2 by yeast. 

 This theory has been attacked by Slator, and Buchner himself has 

 given it up. It may be regarded as of classic interest only. 



One is not able to give up entirely the idea that a large molecule 

 like glucose is not able to be split immediately into small fragments. 



