Abstract
Immunochemical studies were undertaken to investigate qualitative and quantitative differences in N-acetyltransferases from rapid and slow isoniazid acetylator rabbits. Goat anti-N-acetyltransferase antiserum was prepared against partially purified liver N-acetyltransferase from a rapid acetylator rabbit. N-Acetyltransferases found in rabbit erythrocytes, lymphocytes, intestinal mucosa, and livers were tested against this antiserum by Ouchterlony double diffusion. Liver and intestinal mucosal enzyme preparations yielded reactions of complete identity between enzymes in the two tissues and also between enzymes in the two phenotypes, whereas erythrocyte and lymphocyte N-acetyltransferases were nonimmunoreactive. Precipitin reactions between goat anti-N-acetyltransferase and 100,000g liver supernatant fractions from each acetylator genotype yielded equivalent amounts of precipitated protein at nearly identical equivalence points. The antibody titer required to inactivate the sulfamethazine and p-aminobenzoic acid N-acetyltransferase activity in 100,000g liver supernatant fractions was not significantly different for rapid and slow phenotypes, although sulfamethazine N-acetyltransferase activity in rapid acetylator preparations was 10 to 407 times greater than in slow acetylator preparations. Sulfamethazine N-acetyltransferase and p-aminobenzoic acid N-acetyltransferase activities were inactivated at the same rate in both phenotypes. Radial immunodiffusion studies with hepatic supernatant fractions containing equal amounts of p-aminobenzoic acid N-acetyltransferase activity produced precipitin rings with equivalent areas for both rapid (137.5 ± 16.3 mm2) and slow (163.0 ± 46.2 mm2) acetylators. Equal amounts of sulfamethazine N-acetyltransferase activity produced much larger precipitin ring areas for slow acetylator preparations (2443 ± 1389 mm2) than for rapid preparations (27.6 ± 4.1 mm2). These observations are consistent with the following hypotheses: (i) The livers of rapid and slow isoniazid acetylator rabbits contain approximately the same number of N-acetyltransferase molecules, but contain different forms of N-acetyltransferase with markedly different catalytic activities; and (ii) monomorphic (p-aminobenzoic acid) and polymorphic (sulfamethazine) substrates are acetylated by the same N-acetyltransferase molecule.
- Copyright © 1980 by The American Society for Pharmacology and Experimental Therapeutics
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