ENERGY SUPPLY OF THE CELL 45 



acetaldehyde shall be shown here because it is part of 

 the mechanism of alcoholic fermentation. Methyl gly- 

 oxal is written in the hydrated form; the activated 

 H -atoms are shown in heavy type. This compound 

 is the ''hydrogen donator" giving two H-atoms to the 

 acetaldehyde which is the ''hydrogen acceptor.^' 



CH3-C0-C— OH-H2 + CHs-CHO + 2H = 



Methyl glyoxal \ Acet aldehyde 



hydrate ^QH 



CH3COCOOH + CH3-CH20H 



Pyruvic Alcohol 



acid 



This is an example of the "oxido-reductions," the reduc- 

 tion of one molecule by the oxidation of another, which 

 is the essential part of all fermentations. 



By this emphasis on the hydrogen atoms as the 

 essential parts of oxidation and reduction processes, the 

 reactions which we commonly call oxidations would 

 become more precisely "dehydrogenations," and the 

 term dehydrogenase in place of oxidase is used by some 

 biochemists. 



The first step in the fermentation of sugar appears to 

 be the formation of hexose-phosphate, an ester of the 

 sugar with phosphoric acid. This esterification is 

 probably brought about by an enzyme. 



The glucose-phosphate is then split in the middle of 

 the carbon chain, yielding two molecules of glyceric 

 aldehyde, which, according to Kluyver and Struyk 

 (1926), takes place in two steps: 



CeHiaOe + HK2PO4 = C6Hn05(K2P04) + H2O 



CeHuOsCKsPOO = C3H6O3 + C3H502(K2P04) 



Glyceric aldehyde 



