The effects of salicylate on the activity of rat liver tyrosine-2-oxoglutarate aminotransferase in vitro and in vivo.

1. Salicylate, in concentrations of 0.25mm and above, enhances the basal activity of tyrosine-2-oxoglutarate aminotransferase in homogenates of rat liver incubated in the absence of added pyridoxal 5'-phosphate (endogenous activity). The effect is decreased by increasing the concentration of the cofactor. 2. The intraperitoneal administration of sodium salicylate enhances the activity of rat liver tyrosine aminotransferase; the major effect during the first hour being on the enzyme in the absence of added pyridoxal phosphate. Actinomycin D prevents the induction of the enzyme by cortisol and tryptophan. Induction by pyridoxine or salicylate is 50% inhibited by actinomycin D. The effects of the injections of various combinations of cortisol, pyridoxine and salicylate were also studied in the absence or presence of actinomycin D. 3. It is suggested that salicylate induces rat liver tyrosine aminotransferase by displacing its protein-bound cofactor and that a cofactor-type induction of the hepatic enzyme occurs in pyridoxine-treated rats.