272 BACTERIOLOGICAL CHEMISTRY 



action of co-enzyme, for instance. Moreover, methyl- 

 glyoxal has only been isolated following the action of an 

 extract of dried bottom yeast on magnesium hexose 

 diphosphate, and is not itself fermented. 



Neuberg showed that acetaldehyde was an inter- 

 mediate in alcoholic fermentation as a result of " fixa- 

 tion " experiments using calcium sulphite or dimedon 



CH, 



(dimethyl-cyclohexane-dione), | [ , which re- 



C(CH3), 



move the acetaldehyde from further participation in the 

 fermentation either as the insoluble acetaldehyde bisul- 

 phite complex or according to the reaction : — 



CH3 CH3 



I I 

 CH, + CHO+ CH CH CH C 



/\ ^\ /\ ^\ 



CO CO HO.C CO > CO CO HO.C CO 



II II II II 



CHo CH, CH2CH2 CH2CH2 CH2CH2 



C(CH3)2 C(CH3)2 C{CH3)2 C(CH3)2 



in the case of dimedon fixation, with a consequent loss of 

 alcohol production. He also showed that yeast contained 

 the enzyme carboxylase, which could break down «-keto- 

 acids to the aldehyde and carbon dioxide, and, in 

 particular, pyruvic acid, which was also shown to be an 

 intermediate by " fixation " experiments. As a result of 

 these findings he put forward the following scheme for 

 the mechanism of alcoholic fermentation ; glucose is 

 converted into two molecules of methylglyoxal by steps 

 involving phosphorylation : — 



