FUNCTION 



The accumulation of lactic acid as well as pyruvic acid in the blood 

 and tissues of avitaminous animals was at first sight puzzling, but the 

 difficulty was disposed of by W. C. Sherman and C. A. Elvehjem,^^ 

 who pointed out that pyruvic acid completely inhibited lactic de- 

 hydrogenase activity, so that lactic acid accumulated in the tissues 

 instead of being metabolised. By removing pyruvic acid, vitamin 

 Bi thus indirectly brought about the normal metabolism of lactic acid. 

 It has been suggested that the accumulation of methylglyoxal might 

 similarly be due to the inhibition of methylglyoxalase by pyruvate, 

 but there appears to be no direct evidence on this point. 



Pyruvic Acid Metabolism 



Pyruvic acid can be metabolised in various ways. In the presence 

 of air, the acid is oxidised to acetic acid and carbon dioxide : 



(i) CH3 . CO . COOH + O -> CH3 . COOH + CO2, 



and many workers have maintained that this is the reaction catalysed 

 by aneurine. K. Lohmann and P. Schuster ^^ and others, however, 

 hold that in yeast at all events aneurine catalyses the anaerobic 

 decarboxylation to acetaldehyde and carbon dioxide : 



(2) CH3 . CO . COOH . -^ CH3 . CHO + CO2, 



whilst others, e.g. H. A. Krebs,^* H. A. Krebs and W. A. Johnson,^^ 

 and G. M. Hills, ^^ believe that it catalyses a dismutation of the type : 



(3) 2CH3 . CO . COOH ^ CH3 . CHOH . COOH + CH3 . COOH + CO, . 



Aneurine Pyrophosphate 



Actually, aneurine itself is not the catalyst responsible for pyruvic 

 acid metabolism. H. G. K. Westenbrink and J. J. Pollak 2' observed 

 that a period of ten minutes elapsed after the addition of aneurine to 

 polyneuritic brain tissue extract before any uptake of oxygen occurred, 

 and they interpreted this as an indication that aneurine imderwent a 

 change before it could function as a catalyst. The nature of this 

 change was revealed by K. Lohmann and P. Schuster,^^ who isolated 

 from yeast a coenzyme, cocarboxylase, which was found to be the 

 pyrophosphate of aneurine : 



N-C.NH3 9^3 OH OH 



II II C C . CHa . CH3 . O . P . O . P . OH 



CH,.C C-CHa— n/ I II II 



I I / x:h— s o o 



N==CH CI 



93 



