Differences in P-450 Cytochromes from Livers of Rats Treated with Phenobarbital and with 3-Methylcholanthrene

Abstract Soluble P-450 cytochromes were obtained from hepatic microsomes from rats treated with either phenobarbital or 3-methylcholanthrene using the nonionic detergent action of Triton N-101 and the stabilizing effect of glycerol. Ammonium sulfate fractionation, DEAE-cellulose column chromatography, and alumina gel-Cγ adsorption were employed to give concentrations of cytochrome P-450 from phenobarbital-treated rats, and cytochrome P1-450 from 3-methyl-cholanthrene-treated rats, about 4-fold greater than those seen in the microsomes from which the preparations were derived. The spectral characteristics of cytochrome P-450 and P1-450 were very similar, but both qualitative and quantitative differences were observed. Differences were also observed in their carbon monoxide and ethyl isocyanide difference spectra. Type I and type II drug-binding spectra were seen with the solubilized cytochrome P-450, but cytochrome P1-450 gave only the type II binding spectrum. The absolute spectrum of oxidized cytochrome P1-450, and studies which employed tritiated 3-methylcholanthrene, showed that cytochrome P1-450 is not a complex of 3-methylcholanthrene or its metabolites with cytochrome P-450.