ALCOHOLIC FERMENTATION 273 



CgHiaOg ^ 2CH2==('(OH).('H() — ^ L'CHgCO.CHO. 



phosphorylation 



(eiiolic form) (inethylglyoxal) 



These tAvo molecules of inethylglyoxal undergo dismuta- 

 tion (under the influence of the enzyme mutase) to give 

 one molecule of glycerol and one molecule of pyruvic 

 acid : — 



CH2=C(0H).CH0 H2 CH2OH.CHOH.CH2OH (glycerol) 



+ +H2O+ II > 



CH3.CO.CHO CH3.CO.COOH (pyruvic acid). 



The pyruvic acid is then decarboxylated by the enzyme 

 carboxylase to give acetaldehyde and carbon dioxide : — 



CH3.CO.COOH — > CH3CH0 + CO2. 



In the subsequent dismutation of methylglyoxal, one 

 molecule of the latter is replaced by acetaldehyde, which 

 becomes reduced to alcohol, whilst the molecule of 

 methylglyoxal is oxidised to pyruvic acid : — 



CH3.CO.CHO o CH3.CO.COOH 



+ +11 — > + 



CH3CHO H2 CH3CH2OH 



This pyruvic acid in its turn is decarboxylated to give 

 more acetaldehyde, and so the cycle goes on until all the 

 sugar is fermented. 



This, Neuberg's First Form of Fermentation, accounts 

 for the small amount of glycerol, always found in a normal 

 fermentation, as being formed by the reduction of methyl- 

 glyoxal as hydrogen acceptor before the usual acceptor, 

 acetaldehyde, is formed. If the acetaldehyde is trapped 

 and prevented from acting as hydrogen acceptor no 

 alcohol will be formed, and methylglyoxal will continue 

 to act as hydrogen acceptor and yield a molecule of 

 glycerol for every molecule of carbon dioxide formed 

 and every molecule of aldehyde fixed. This is Neuberg's 

 Second Form of Fermentation. Neuberg also established 

 a Third Form of Fermentation, which takes place if the 



