IMMUNOLOGICAL EVIDENCE FOR N-ACETYLTRANSFERASE ISOZYMES IN THE RABBIT

An immunological evaluation of N-acetyltransferase (NAT) (EC 2.3.1.5) in liver, duodenum, lung, and kidney of the rabbit is described. Polyclonal antibodies to hepatic NAT isolated from rapid acetylator rabbits were raised in a goat and utilized for immunoblot analyses and enzyme inhibition studies. Immunoblot analyses demonstrated that hepatic and duodenal cytosols from rapid but not slow acetylator rabbits contained an immunoreactive 33-kDa protein. No immunoreactivity was observed for lung or kidney cytosols from either rapid or slow acetylators. The inhibition of sulfamethazine and p-aminobenzoic acid acetylation by polyclonal antibodies was investigated using cytosols from rapid and slow acetylator rabbits. With rapid acetylator cytosols, maximal inhibition of hepatic, duodenal, and lung NAT activities was 94.4 +/- 9.0%, 92.5 +/- 8.5%, and 28.3 +/- 2.4%, respectively, for sulfamethazine (500-mu-M) acetylation and 90.1 +/- 8.0%, 80.2 +/- 6.4%, and 26.7 +/- 3.1%, respectively, for p-aminobenzoic acid (500-mu-M) acetylation. Using 25-mu-M p-aminobenzoic acid as substrate, maximal inhibition of NAT activity was 32.0 +/- 2.1% with liver cytosol and 5.8 +/- 0.16% with duodenal cytosol, whereas no inhibition of lung NAT activity was observed. Kidney NAT activity was not inhibited by the polyclonal antibodies. With slow acetylator cytosols, no inhibition of NAT activities was observed. It is concluded that at least two NATs are present in liver, duodenum, and lung of rapid acetylator rabbits. Furthermore, the principal NAT in liver and duodenum is immunologically related to the minor form of lung NAT and is antigenically distinct from kidney NAT of rapid acetylators. Hepatic, duodenal, lung, and kidney NAT(s) of slow acetylator rabbits is (are) immunologically distinct from the major hepatic NAT in rapid acetylators. The data support the model in which the hepatic polymorphism in rabbits is caused by the total lack of the major rapid acetylator hepatic NAT in the phenotypic slow acetylator animal. These observations may have significant implications in the organspecific toxicities of carcinogens that undergo metabolic activation via N-acetylation.