D-AMINO ACID OXIDASE 



341 



Benzoates and Related Compounds on D-Amino Acid Oxidase 



The oxidation of D-alanine in slices and homogenates of rat liver and 

 kidney was shown to be markedly inhibited by 1 mM benzoate by Klein and 

 Kamin (1941). A preparation of D-amino acid oxidase from pig kidney was 

 thus obtained and found to be inhibited 79% by 0.1 mM, this being rever- 

 sible upon dialysis. Several substituted benzoates are also inhibitory but 

 all are less potent than benzoate; benzamide is inactive. The inhibitions of 

 a lamb kidney D-amino acid oxidase by benzoate and j9-amino-benzoate 

 were shown by Hellerman et al. (1946) to be competitive with substrate. 

 The rate of spontaneous inactivation of the apoenzyme is reduced by either 

 substrate or FAD, and benzoate was shown by Burton (1951 a) to have a 

 comparable action, indicating combination with the active center. 



Before discussing the more detailed mechanism of the inhibition we 

 shall turn to three studies providing information on the structural require- 

 ments for inhibition. Bartlett (1948) compared many substituted benzoates 

 (Table 2-15) and found only four to be more potent inhibitors than benzoate, 



Table 2-15 

 Inhibition of Pig Kidney d-Amino Acid Oxidase by Substituted Benzoates " 



" The substrate is DL-alanine at 30 mM and the pH 7.6. Binding energies calculated 

 from concentrations for 50% inhibition. (Data from Bartlett, 1948.) 



pure competitive inhibition with respect to substrate being observed. 

 J. R. Klein (1953, 1957) demonstrated inhibition, often potent, by various 

 aromatic carboxylates (Table 2-16), and Frisell et al. (1956) provided further 



