ALCOHOLIC FERMENTATION 271 



H t[ H H 



CHO C^ — OH C^-— OH C OH C— OH 



1 +H2O ', \0H — H,.0 I \ I \0 I \0H 



CHOH . CHOH ^>CHOH\o > HOC— I — - CO 



I I III I 



CH.OH CH2OH CH2 1 CH3 CH3 



(glyceral- (plvccraldc- (mcthylglyoxal 



dnhyde) liycle hydratv^ liydrate) 



The methylglyoxal hydrate loses hydrogen to acetaldehyde 

 (or some other hydrogen acceptor at the beginning of the 

 fermentation, before acetaldehyde is formed) to form 

 pyruvic acid, the acetaldehyde being at the same time 

 reduced to alcohol. 



OH COOH 



CO 



CH3 



The p^Tuvic acid is decarboxylated to give carbon dioxide 

 and acetaldehyde, which acts as hydrogen acceptor for 

 the production of further supplies of pyruvic acid from 

 methylglyoxal hydrate : — 



COOH CO2 



I + 



CO > CHO 



I I 



CH3 CH3 



The only enzymes involved in this scheme are phosphatase, 

 hydrogen transportase and carboxylase. 



The evidence for this scheme is based, in the main, 

 on analysis of the proportions of the various products 

 formed and misses many of the steps which are now 

 known to take place ; it does not take account of the 



