SUBSTRATE SELECTIVITY OF MOUSE N-ACETYLTRANSFERASE-1, N-ACETYLTRANSFERASE-2, AND N-ACETYLTRANSFERASE-3 EXPRESSED IN COS-1 CELLS

Two human acetyl-CoA:arylamine N-acetyltransferases (NAT1 and NAT2) ha ve been identified. Therapeutic and carcinogenic agents that are subst rates for these isoenzymes (including isoniazid, sulfamethazine, p-ami nobenzoic acid, 5-aminosalicyclic acid, and P-aminofluorene) have been used to evaluate the role of the N-acetylation polymorphisms of NAT1 and NAT2 in the treatment of disease and differential risk of various cancers among individuals of differing acetylator phenotypes. The mous e is frequently used as a model of the human acetylator polymorphism. As three Nat isoenzymes have been identified in mouse, it is necessary to determine the selectivity of mouse Nats toward common NAT substrat es. In the present study, Nat1, Nat2*8, and Nat3* were expressed in C OS-l cells, and their substrate selectivity was evaluated with various substrates. Under the conditions used, mouse Nat2 had 20-, 2.4-, and 5.4-fold higher catalytic activity for p-aminobenzoic acid, 5-aminosal icylic acid, and 5-aminofluorene, respectively, than Natl. Isoniazid N -acetylation was catalyzed only by mouse Natl. For the substrates test ed in this study, mouse Nat3 exhibited activity only toward 5-aminosal icylic acid and only at 1/20 the activity shown by Nat2. In addition, p-aminobenzoylglutamate, the first endogenous NAT substrate identified , was selective for mouse Nat2, These results further support the func tional analogy of mouse Nat2 and human NAT1.