ANEURINE (thiamine) 



was obscured under aerobic conditions, owing to partial oxidation of 

 the lactic acid. Lactate was utilised as a substrate only imder aerobic 

 conditions and, in the presence of aneurine and nicotinic acid, was 

 completely oxidised to acetic acid and carbon dioxide ; in the absence 

 of aneurine, oxidation was incomplete, 25 % of the lactic acid being 

 converted to pyruvic acid. 



H. A. Krebs and L. V. Eggleston ^^ and H. A. Krebs,*^ suggested 

 that reaction (3) actually occurs in two stages, in which oxaloacetic 



acid acts as a hydrogen carrier : 



+ H20 



(4) CH3 . CO . COOH + HOOC . CH2 . CO . COOH ^ 



CH3 . COOH + HOOC . CH2 . CHOH . COOH + CO, 



(5) CH3 . CO . COOH + HOOC . CHa . CHOH . COOH > 



CH3 . CHOH . COOH + HOOC . CH, . CO . COOH 



The net result of these reactions is, of course, reaction (3). 



The formation of oxaloacetic acid, which cannot be isolated owing 

 to its instability, was demonstrated indirectly by E. A. Evans and 

 L. Slotin ** and H. G. Wood et al.,^^ using carbon dioxide containing 

 radioactive carbon. Furthermore, D. H. Smyth *® showed that the 

 catalytic effect of aneurine on the oxygen uptake of " avitaminous " 

 Staphylococcus aureus could be reproduced by oxaloacetic acid, and 

 R. W. Benham *^ observed that oxaloacetate produced the same 

 effect as aneurine on the growth of the mould, Pityrosporum ovale. 

 Krebs suggested that aneurine catalyses not the oxidation of pyruvic 

 acid, but the formation of oxaloacetic acid from pyruvic acid : 

 (6) CH3 . CO . COOH -f COa -> HOOC . CH^ . CO . COOH. 



So far this hypothesis has not been tested on animals, but, if true, 

 it would provide a more than adequate explanation of the importance 

 of aneurine, since oxaloacetic acid has been shown to act as a hydrogen 

 carrier and to take part in the synthesis of citric, a-ketoglutaric, 

 succinic, fumaric and malic acids, glutamic and aspartic acids and 

 their corresponding amides, glutamine and asparagine (Krebs et al.^^). 



Citric Acid 



A number of papers have been published claiming a connection 

 between aneurine on the one hand and citric acid and various amino 

 acids on the other. It has been observed,'*^ for example, that rats on 

 a vitamin B^-deficient diet low in citric acid, excreted less and less 

 citric acid as the deficiency became acute, but that on administra- 

 tion of aneurine, the citric acid excretion increased to a maximum 

 after four to six days. It was therefore suggested that cocarboxylase 

 was an essential factor in the synthesis of endogenous citric acid from 



96 



