Cysteine S-conjugate N-acetyltransferase from rat kidney microsomes

Abstract

An acetyltransferase from rat kidney microsomes that catalyzes the N-acetylation of thioethers of L-cysteine has been solubilized, stabilized, and separated from hydrolytic enzymes active against both the acetylated product, a mercapturic acid, and acetyl coenzyme A. Efficiency of catalysis varies with the lipophilicity of the substituent at sulfur in the order, ethyl < propyl < benzyl < butyl, as predicted by the Hansch π constants. Although L-tryptophan is acetylated at a very low rate, acetylation is not detectable for L-cysteine, L-methionine, L-serine, L-leucine, L-phenylalanine, or L-glutamic acid. The properties and substrate specificity reported here, along with previous studies on enzyme distribution, suggest that cysteine S-conjugate N-acetyltransferase is responsible for the final step in mercapturic acid biosynthesis.