RECOMBINANT EXPRESSION AND CATALYTIC ANALYSIS OF RAPID AND SLOW ACETYLATOR SYRIAN-HAMSTER CHIMERIC NAT2 ALLELES

Polymorphic aromatic amine N-acetyltransferase (NAT2) catalyzes the N- acetylation of aromatic amines and the metabolic activation of N-hydro xyarylamines (via O-acetylation) and N-hydroxy-N-acetylarylamines (via N,O-acetylation) to electrophilic intermediates that mutate DNA. Acet ylation capacity in humans and other mammalian species such as Syrian hamsters is subject to a genetic polymorphism. NAT2 is regulated by a single gene (NAT2) containing a single coding exon of 870 bp. Syrian h amster slow acetylator differs from the rapid acetylator NAT2 coding r egion by three nucleotide substitutions at (TC)-C-36, A(633)G and (CT) -T-727. We measured expression of immunoreactive NAT2 protein and arom atic amine N-acetylation, N-hydroxyarylamine O-acetylation and N-hydro xy-N-acetylarylamine N,O-acetylation by recombinant NAT2 proteins expr essed from alleles containing all combinations of the (TC)-C-36, A(633 )G and (CT)-T-727 substitutions. The (CT)-T-727 substitution, which cr eates an opal stop codon in slow acetylator NAT2, was the sole mutatio n responsible for substantial reduction in expression of a truncated N AT2 protein with reduced capacity for the deactivation of aromatic ami nes (N-acetylation) and the metabolic activation of N-hydroxyarylamine s (O-acetylation) and N-hydroxy-N-acetylarylamines (N,O-acetylation). The reductions in aromatic amine N-acetylation correlated very highly with the reductions in metabolic activation of the corresponding N-hyd roxyarylamines and N-hydroxy-N-acetylarylamines.