384 ENZYMES 



This discovery of the effect of adding sulphites to the fer- 

 menting mixture assumed technical importance in Central 

 Europe during the great shortage of fats. The yield of glycerol 

 obtained by this process amounted in some cases to over 20 

 per cent and by employing concentrations of sodium sulphite 

 equivalent to 200 per cent of the sugar concentration, a yield 

 of 36*7 per cent was obtained.* 



According to Buchner, lactic acid is an intermediate pro- 

 duct of fermentation ; in the first place the glucose under the 

 influence of zymase is converted into lactic acid, which is then 

 attacked by another enzyme, the action giving origin to carbon 

 dioxide and alcohol. 



Kohl,f however, points out that lactic acid is not fermented 

 by zymase, by compressed yeast nor by bottom yeast ; indeed 

 I per cent lactic acid is sufficient to stop the auto-fermentation 

 of yeast and to reduce greatly the fermentation of glucose. 

 On the other hand, zymase will ferment sodium lactate, which 

 indicates that if lactic acid is an intermediate product of fer- 

 mentation, according to Buchner's view, a salt rather than the 

 acid must be formed. 



In yeast-extract Kohl found an enzyme, catalase, which 

 was capable of oxidizing phenols. The yeast-extract on 

 filtering produces lactic acid in the presence of glucose, and 

 the acid in the presence of zymase is converted into alcohol 

 and carbon dioxide; if, however, zymase be not present, 

 oxidation may go further and other acids be produced. 



Briefly put, he considers that the glucose, by the action of 

 catalase, is converted into lactic acid which is operated upon 

 by zymase, so that alcohol and carbon dioxide are produced. 



Lebedev | considers that the balance of evidence is not 

 favourable to the view that lactic acid is an intermediate pro- 

 duct ; he considers that pyruvic aldehyde is more likely, 

 although the evidence is not conclusive, since at low concen- 

 trations it is decomposed by yeast to practically equivalent 

 amounts of alcohol and carbon dioxide. 



Zymase-like enzymes are not restricted to the yeasts : such 



* Connstein and Liidecke : " Ber. deut. chem. Gesells.," 1919, 52, 1385. See 

 also Zerner : " Ber. deut. chem. Gesells.," 1920, 53, [B], 325. 

 fKohl: " Beih. hot. Centrlbl.," 1910, 29, 115. 

 JLebedev: " Biochem. Journ.," 1917, n, 189. 



