ANTIBODY AS A SPECIFIC ENZYME INHIBITOR 167 



effect of 0.034 M oxalic, malonic, glutaric, adipic, 1-aspartic, 1-malic 

 and fumaric acids on the oxidation of succinic acid was determined. 

 Malonic and oxalic acids exercised most marked inhibition, while 

 glutaric, adipic and aspartic acids inhibited about 25 per cent, and 

 fumaric acid 24 per cent. The last is the first oxidation product of suc- 

 cinic acid. 



In these cases also the inhibition of succinic acid oxidation by 

 malonic acid would seem to be easily explainable on the basis of an 

 affinity between succinic acid dehydrogenase and malonic acid, owing 

 to the similarity of configuration. Since malonic acid cannot be de- 

 hydrogenated, unlike the activated succinic acid, it does not readily dis- 

 sociate from the enzyme and consequently blocks the enzyme from re- 

 acting with succinic acid. The inhibition of succinoxidase by the other 

 acids must likewise be attributed to its property of combining with com- 

 pounds possessing affinities similar to succinic acid. 



7. Inhibitory Effect of the Salts of Organic Acids on the 

 Oxidation of Tyrosine by Tyrosinase 



With the object of finding an analogy to the inhibition phenomenon 

 observed in precipitin reactions with organic acids, isomeric with or 

 structurally related to those coupled vdth proteins, Landsteiner and 

 van der Scheer (1927) examined the effect of 41 sodium salts of 

 organic acids on the action of the oxidase of potatoes and mushrooms 

 on tyrosine (p-hydroxyphenyl-a-aminopropionic acid). In a general 

 way they stated that carboxylic acids of benzene and other cylic com- 

 pounds acted more strongly than fatty acids, and that stronger inhibi- 

 tion was caused by the meta and para substituted acids than by the 

 ortho substituted. 



8. Inhibition of Lactic Acid Dehydrogenase by the 

 Reaction Product Pyruvic Acid 



Green and Brosteaux (1936) in their study of the mechanism of 

 the dehydrogenation of lactic acid by enzyme solutions prepared from 

 animal tissues observed that there was a rapid oxygen uptake by 

 the system during the first five to 10 minutes, and then the rate fell 



