490 ENZYMES 



succinic acid, fusel oil, and glycerol. The formation of glycerol 

 was explained by Neuberg and Kerb * by a series of equations 

 according to which a molecule of glucose gives rise to two 

 molecules of pyruvic aldehyde (methylglyoxal) as follows : — 



(i) CgHijOe - 2H2O = 2CH3CO . COH. 



pyruvic aldehyde. 



The two latter then undergo a Cannizarro reaction, one mole- 

 cule being oxidised and the other reduced, with the formation 

 of a molecule each of glycerol and pyruvic acid. 



CH2 = C(OH) . CHO + H2O H2 CH.,OH . CHOH . CH,OH 

 (2) + II = glycerol 



CHj = C(OH) . CHO O CH3 . CO . COOH 



pyruvic acid 



The pyruvic acid so formed is converted by carboxylase into 

 acetic aldehyde and carbon dioxide. 



(3) CH3 . CO . COOH = CH.CHO + CO^ 



acetic aldehyde 



Finally the acetic aldehyde undergoes another Cannizarro 

 reaction with more pyruvic aldehyde with formation of ethyl 

 alcohol and pyruvic acid. 



(4) 



CH. . CO . CHO O CH; 



pyruvic acid 



The pyruvic acid being converted into acetic aldehyde again 

 according to equation (3). 



The shortage of glycerol experienced by the Central 

 Powers during the World War led to a reinvestigation of this 

 reaction with a view to its technical exploitation. This was 

 successfully accomplished by the observation that addition 

 of sodium sulphite to a fermenting mixture was able to in- 

 crease the yield of glycerol from its normally very low value 

 up to about 20 per cent of the weight of the sugar employed ; 

 by employing concentrations of sodium sulphite equivalent to 

 200 per cent of the sugar concentration, a yield of 367 per cent 

 was obtained. t 



To explain this increased formation of glycerol, it is sug- 



*Neubergand Kerb: " Biochem. Zeit.," 1913,58, 158. 



t Connstein and Liidecke : " Ber. deut. chem. Gesells.," 1919, 52, 1385. 

 Zerner : id., 1920, 53, [B.], 325. Tomoda : " J. Fac. Eng. Tokyo," 1924, 

 15. 193- 



