Enhancement by cyanide of aniline p-hydroxylation activity in rat liver microsomes

Abstract Aniline p -hydroxylation activity of rat liver microsomes was found to be enhanced, rather than inhibited, at aniline concentrations higher than about 3 mM. The cyanide-induced enhancement increased as the oxygen tension was increased. The activation by cyanide was, however, significantly diminished with liver microsomes from phenobarbital- and 3-methylcholanthrene-pretreated rats. The enhancement was also decreased when liver microsomes were fortified with NADPH-cytochrome P-450 reductase. Aniline hydroxylation by reconstituted systems consisting of partially purified preparations of several species of cytochrome P-450 and the reductase was inhibited by cyanide, though the degree of inhibition was dependent on the species of cytochrome P-450 used for reconstitution. In several respects, the cyanide-induced enhancement of aniline hydroxylation is different from the enhancement caused by acetone and 2,2'-bipyridine, but is similar to the activation by ethylisocyanide.