50 PHYSIOLOGY OF BACTERIA 



IIIc. CHa-CO-C— OH = CHg-CO-COOH + 2H 



\ Pyruvic acid 



Methyl glyoxal hydrate 



IVe. CH3-CH0 + 2H = CH3CH2OH 



Acet aldehyde Alcohol 



The combination of these two equations has been given 

 on p. 45 as an example of a typical oxido-reduction. 

 The pyruvic acid which comes from methyl glyoxal, is 

 changed to acet aldehyde according to equation Ic 



Ic: CH3COCOOH = CH3-CH0 + CO2 



The acet aldehyde thus formed can react again as 

 acceptor for the hydrogen from a new methyl glyoxal 

 molecule and the final sum of these reactions is the sum 

 formula of the alcoholic fermentation. Only at the very 

 start, a certain amount of acet aldehyde, or other hydro- 

 gen acceptor, must be present to bring about the first 

 pyruvic acid molecules. 



There are other possibilities hidden in the yeast 

 mechanism. Small amounts of glycerol are formed, and 

 this is due to the glyceric aldehyde acting as hydrogen 

 acceptor in place of the acet aldehyde : 



Ic: CHsCO-C— OH - 2H = CH3COCOOH 



Methyl glyoxal \ Pyruvic acid 



^OH 

 IVc: CH2OHCHOHCHO + 2H = 



Glyceric aldehyde 



CH20H-CHOHCH20H 



Glycerol 



While acet aldehyde seems to be more efficient as 

 hydrogen acceptor, glycerol will be formed in large 



