Abstract

Kinetic parameters (ki and KI) were determined in vitro for the suicide inactivation of hamster hepatic N-arylhydroxamic acid N,O-acyltransferase by N-hydroxy-2-acetamidofluorene and N-hydroxy-4-acetamidobiphenyl. The inhibition of hamster hepatic N-arylhydroxamic acid N,O-acyltransferase by N-hydroxy-2-acetamidofluorene was not reversed by incubation with cysteine. Partial protection of the enzyme against inactivation was observed with low molecular weight nucleophiles (e.g., cysteine). Hamster hepatic CoASAc-dependent N-acetyltransferases were inactivated irreversibly by incubation with N-hydroxy-2-acetamidofluorene. p-Aminobenzoic acid CoASAc-dependent N-acetyl-transferase activity, but not sulfamethazine CoASAc-dependent N-acetyltransferase activity, was protected against inactivation when cysteine was included in the incubation mixtures. Therefore, although hamster hepatic CoASAc-dependent sulfamethazine N-acetyltransferase may be associated with N-arylhydroxamic acid N,O-acyltransferase, the CoASAc-dependent p-aminobenzoic acid N-acetyltransferase appears to be a different enzyme. The use of N-arylhydroxamic acids as suicide substrates is a promising technique for probing the mechanism of N-arylhydroxamic acid N,O-acyltransferase-mediated reactions, for exploring the relationships between N-arylhydroxamic acid N,O-acyltransferase and CoASAc-dependent N-acetyltransferases, and for selective inactivation in vitro of multiple forms of CoASAc-dependent N-acetyltransferases.