ENZYME-KINETIC PROPERTIES OF HUMAN RECOMBINANT ARYLAMINE N-ACETYLTRANSFERASE-2 ALLOTYPIC VARIANTS EXPRESSED IN ESCHERICHIA-COLI

Arylamine N-acetyltransferase (NAT2) catalyses the N-acetylation of pr imary arylamine and hydrazine drugs and chemicals. N-Acetylation is su bject to polymorphism, and humans can be categorized as either fast or slow acetylators according to their ability to N-acetylate certain ar ylamine substrates in vivo. Genetic variants at the polymorphic NAT2 l ocus have been described. We expressed five of the most common NAT2 va riants (NAT2 4, NAT2 5A, NAT2 5B, NAT2 6A and NATZ, 7B) in Escherichia coli as a convenient source of the human variants. The apparent K-m v alues (at 100 mu M acetyl CoA as co-substrate) of the different NAT2 v ariants for sulphamethazine, dapsone, p-anisidine, 2-aminoAuorene, pro cainamide and isoniazid were determined. Data show that the apparent K -m of the slow variant NAT2 7B for the arylamine sulphamethazine was 1 0-fold lower than all the other allotypes. The apparent K-m for the st ructurally related sulphone antibiotic dapsone was 5-fold lower for th e slow variant NAT2 7B when compared with the wild-type NAT2 4. These results indicate that the NAT2 7B specific amino acid substitution, Gl y286-Glu, is important in promoting the binding of sulphamethazine and dapsone to the active site.