168 IMMUNO-CATALYSIS 



off sharply. The fall of the rate of oxygen uptake was so marked that 

 at the end of one hour the final uptake was only slightly greater than 

 at the end of the first few minutes. This effect was held to be due either 

 to (a) the rapid destruction of the enzyme, or that (b) some product 

 of the reaction inhibited the enzyme very strongly. The product of 

 the reaction was assumed to be pyruvic acid and this assumption was 

 confirmed by the fact that by the addition of cyanide to the system and 

 thus by the formation of cyanhydrin, the accumulation of pyruvic acid 

 was prevented. In the presence of an optimal concentration of cyanide 

 the rate of the oxidation of lactate was increased markedly. The 

 beneficial effect of cyanide was formulated as follows: 



CH3COCOOH+HCN ^ CH3C-COOH 



l\ 

 I CN 

 OH 



To confirm their assumption they added an excess of pyruvate and 

 abolished the effect of cyanide; addition of a small amount of pyru- 

 vate had no effect. That the rapid fall of the oxygen uptake by lactate 

 was due to pyruvate as reaction product was also demonstrated by 

 adding 0.05 M pyruvate to the system at the beginning of the experi- 

 ment in the absence of cyanide. This concentration of pyruvate com- 

 pletely inhibited the oxidation of lactic acid. While 0.04 M pyruvate 

 inhibited the oxidation of l(+)-lactate 100 per cent, 0.03 M tartronate 

 inhibited 60 per cent by virtue of configurational similarity to both 

 the substrate and the reaction product. 



The enzyme system studied by Green and Bostreaux shows a spec- 

 ificity similar to the high degree of serological specificity shown by 

 antibodies against the optical, or d- and 1-isomers of haptens coupled 

 with proteins. Though it oxidizes Mactate rapidly it has no effect on 

 d-lactate, nor does a 0.03 M concentration of the latter exercise an 

 inhibitory effect on the enzyme activity. 



9. Inhibition of the Dehydrogenases of Succinic, Lactic 

 and Mahc Acids by Their Reaction Products 



Das (1937a) investigated the affinity of lactic dehydrogenase 

 towards both malic and lactic acids. The enzyme systems he used were 



