Studies with tryptophan metabolites in vitro—II: Effect of tartar emetic on kynurenine metabolism by normal mouse liver

Abstract Potassium antimonyl tartrate (tartar emetic) inhibited the conversion of kynurenine to both kynurenic and anthranilic acids in normal mouse liver homogenates. The inhibition is mainly due to a reduction in the level of active pyridoxal. Since the inhibition is easily reversed by the supplementation of exogenous pyridoxal phosphate but not with pyridoxal and ATP, it would seem that tartar emetic inhibited the phosphorylation of pyridoxal. Similar inhibitory effects on the metabolism of kynurenine were observed with deoxypyridoxine phosphate. The latter inhibition is removed in presence of a specific concentration of tartar emetic. The antimony moiety of tartar emetic appears to form an inactive chelate with both pyridoxal phosphate and deoxypyridoxine phosphate which replaces the active counterpart at the active sites of both kynureninasc and kynurenine transaminase enzyme systems. Evidence for the formation of these chelates was obtained spectrophotometrically.