ALCOHOLIC FERMENTATION 277 



Phosphopyruvic acid is now dephosphorylated by adeno- 

 sine diphosphate to give pyruvic acid and adenosine 

 triphosphate which hands on its phosphate groups to 

 fresh hexose molecules. Pyruvic acid is decarboxylated in 

 presence of the enzyme, carboxylase, to give acetaldehyde 

 and CO2 : — 



CUOH CO., 



I + CHO 



CO > 



I 



The acetaldehyde is reduced by dih^^lro -co -enzyme I 

 to give ethyl alcohol : — 



CHO CH2OH 



I + Dihydro- CO -enzyme I > \ + Co-enzyme I 



CH3 (-H3 



The CO -enzyme I thus becomes available again to oxidise 

 3-phosphoglyceraldehyde to more 3-phosphoglyceric acid, 

 and the cycle is maintained. 



The reactions outlined above represent the " Stationary 

 condition," in which acetaldehyde acts as hydrogen 

 acceptor from dihydro -co -enzyme I. In the " Initial 

 phase," as Meyerhof calls it, before any acetaldehyde is 

 available 3-phosphoglyceraldehyde is dismuted with 

 formation of a -glycerophosphate and 3-phosphoglyceric 

 acid. The latter is involved in the series of reactions 

 already described with the ultimate production of CO2 

 and alcohol whilst the « -glycerophosphate is hydrolysed 

 to form glycerol and pliosphate. It is in this way that the 

 2 to 3 per cent, of glycerol jjroduced in a normal alcoholic 

 fermentation arises. The initial phase can be inhibited 

 by fluoride which prevents the utilisation of the 3-phospho- 

 glyceric acid. The effect of fluoride can be overcome 

 by adding acetaldehyde so that the initial phase is 

 " by-passed." If acetaldehyde is fixed by addition of 

 siilpliite or (limedon. or if the stationary (•(Hiditioii is 



