RESPIRATION AND FERMENTATION 263 



treating yeast cells with acetone or by carefully drying them and 

 subsequently extracting with water, which, of course, considerably 

 facilitated investigation of the enzyme. Further studies have 

 shown that zymase is not a single enzyme, but a complex of several 

 enzymes. This agrees with the fact that alcoholic fermentation 

 is a very complex process proceeding through several separate 

 phases. 



Not all of the phases of alcoholic fermentation have been def- 

 initely determined as yet, but recent investigators, notably Neu- 

 berg and his co-workers, and Kostytschev, have brought us nearer 

 to the solution of this question. According to these investigations, 

 the most important intermediate products in fermentation are 

 pyruvic acid, CH 3 • CO • COOH and acetaldehyde, CH 3 • COH. In 

 their details the mechanisms as proposed by Kostytschev and by 

 Neuberg differ considerably. 



Kostytschev supposes that the first phase comprises the elimina- 

 tion of hydrogen from sugar, attended by the formation of pyruvic 

 acid C 6 Hi 2 6 = 2CH 3 COCOOH + 4H, the hydrogen being 

 bound by special hydrogen acceptors. Then under the influence of 

 carboxylase, a special enzyme splitting off CO2, pyruvic acid is 

 converted into aldehyde and carbon dioxide, CH3COCOOH = 

 CH3 • COH + CO2. Finally, the formed aldehyde is reduced by 

 the previously bound hydrogen to alcohol, 



CH3COH + 2H = CH3CH2OH. 



Kostytschev indicates that the first part of his theory is of a purely 

 hypothetical character. 



In Neuberg' s proposed mechanism a great role is played by the 

 Cannizzaro reaction, i.e., the conversion of 2 molecules of aldehyde, 

 with addition of water, into 1 molecule of acid and 1 molecule of 

 alcohol, through mutual interchange of oxygen and hydrogen. 

 Neuberg considers methylglyoxal, CH3COCOH, as the first 

 product of fermentation, which then by way of transmutation 

 under the influence of a special enzyme, mutase, produces glycer- 

 ine and pyruvic acid. The latter splits into CO2 and acetalde- 

 hyde, CH3-COH, which in its turn produces pyruvic acid and 

 alcohol. 



Besides Kostytschev's and Neuberg's hypotheses, there have 

 been proposed also other ideas. Both Buchner and Palladin, for 



