An enzyme marker to ensure reliable determinations of human isoniazid acetylator phenotype in vitro.

Human liver N-acetyltransferase (NAT) activity undergoes rapid inactivation after death. Thus, in vitro determination of acetylator phenotype in liver autopsies may be unreliable. In the present investigation, the relative stabilities of monomorphic and polymorphic NAT activity were compared in situ in human and rabbit liver of rapid and slow acetylator phenotype. In both phenotypes, the monomorphic NAT activity was considerably less stable than the polymorphic, enabling it to be utilized as an enzyme marker to assure reliable in vitro phenotype classification.