Evidence for two closely related isozymes of arylamine N‐acetyltransferase in human liver

Abstract
Acetyl CoA‐dependent arylamine N‐acetyltransferase (EC 2.3.1.5) is the target of a genetic polymorphism in the metabolism of drugs and carcinogens. N‐Acetyltransferase was purified 1000‐fold from cytosol of human liver and its identity was verified by amino acid sequence homology of two of its tryptic peptides with published rabbit and chicken N‐acetyltransferase sequences. Enzyme activity correlated with the presence of two proteins, NAT‐1 and NAT‐2, with indistinguishable molecular masses (31 kDa). NAT‐1 and NAT‐2 could be separated by anion‐exchange chromatography and were functionally distinguished by their different apparent affinities for the acceptor amine sulfamethazine (SMZ). Antibodies raised against NAT‐1 were able to recognize both isozymes on Western blots.