Hydroxylation of benzphetamine and other drugs by a solubilized form of cytochrome P-450 from liver microsomes: Lipid requirement for drug demethylation

Abstract

A solubilized hepatic microsomal enzyme system previously shown to catalyze the [omega]-hydroxylation of fatty acids also catalyzes the hydroxylation of drugs. Benzphetamine, aminopyrine, ethylmorphine, hexobarbital, norcodeine, and -nitroanisole undergo aerobic demethylation in the presence of NADPH and the resolved enzyme system. The required submicrosomal components for benzphetamine demethylation, as determined either by formaldehyde liberation or by NADPH oxidation, are cytochrome P-450, NADPH-cytochrome P-450 reductase, and a heat-stable lipid fraction. Similar requirements were shown for the oxidation of aminopyrine, ethylmorphine, and hexobarbital. Laurate and benzphetamine were found to be mutually inhibitory, as would be expected if a common "methyl hydroxylase" were involved. The solubilized cytochrome P-450 preparation exhibits a difference spectrum in the presence of benzphetamine with a peak at 392 m[mu] and a trough at 427 m[mu] and difference spectra with aniline and hexobarbital typical of those obtained with the microsomal bound form of this hemoprotein.