340 2. ANALOGS OF ENZYME REACTION COMPONENTS 



The L-amino acid oxidase from the hepatopancreas of Cardium tubercula- 

 tum is more specific than the venom or kidney oxidases, since many L-amino 

 acids are not oxidized but are inhibitory (Roche et al., 1959). The inhibitions 

 by 16.7 mM L-leucine are shown in the following tabulation. At pH 7.6 

 the inhibitions are competitive, but not at pH 9.2. Apparently this enzyme 

 can complex with both l- and D-isomers although in no case is a direct 

 comparison possible. 



D-AMINO ACID OXIDASE 



D-Amino acid oxidase is also inhibited by certain amino acids, but no 

 thorough studies have been reported. The enzyme from pig kidney oxidizing 

 D-leucine is inhibited by DL-leucinamide, DL-leucylglycine, glycyl-DL- 

 leucine, and DL-leucylglycylglycine, but not glycylglycine (Heimann- 

 Hollaender and Lichtenstein, 1954). It is interesting that the oxidation 

 of D-phenylalanine is inhibited by DL-iV-ethylphenylalanine and the oxida- 

 tion of D-leucine by DL-A^-ethylleucine, since A'-substituted amino acids are 

 usually not inhibitory for any enzymes acting on amino acids. D-Lysine is 

 a good inhibitor of this enzyme oxidizing D-alanine (Ky„ = 3.3 mM, and 

 K^ = 5 mM), but L-lysine is completely inactive (Murachi and Tashiro, 

 1958). The D-amino acid oxidase from pig kidney with glycine as a substrate 

 is competitively inhibited by L-leucine {K, = 1 mM) (Neims and Hellerman, 

 1962). Pyruvate not only competes with D-alanine {K^ = 43 mM) but accel- 

 erates the photodecomposition of FAD (Yagi and Natsume, 1964). However, 

 the most interesting and best studied inhibition of D-amino acid oxidase is 

 that of benzoate and its derivatives, and the opportunity will be taken in 

 this section of discussing not only the actions of the benzoates on this en- 

 zyme but also on other enzymes and metabolism in general. 



