[Relation between the drug-metabolizing activities of liver microsomes and multiplicity of cytochrome P-450 (author's transl)].
Wada et al. found a hyperbolic curve in the Lineweaver-Burk plots of the drug-metabolizing activity and competitive inhibition of steroid hormones to drugs, and suggested that several enzymes acting on different sites of various steroid hormone molecules might metabolize drugs without having specificities for hydroxylation sites. Recently, several cytochrome P-450s were separated and purified from liver microsomes. We studied the relation between the drug-metabolizing activities and multiplicity of cytochrome P-450 with the pH curve and the Lineweaver-Burk plots. Phenobarbital- and methylcholanthrene-treatment had remarkable effects on the pH curve of aniline hydroxylation by mouse liver microsomes. Addition of cortisol inhibited aniline hydroxylatin by liver microsomes from phenobarbital-treated mice more effectively at higher pH range and the pH curve was similar to that seen for normal mice. Haugen and Coon separated preparations [A] [B] and [C] with hydroxylapatite chromatography and we obtained [A'] (eluted by 100 mM K-phosphate buffer, pH 7.4) between [A] (50 mM) and [B] (300 mM). The preparation [A'] had the same absorption maximum (451 nm) of reduced CO complex as [A], but Km and pH curve for [A'] were similar to those for [B]. Each separated preparation of cytochrome P-450 showed a hyperbolic curve in Lineweaver-Burk plots and a different pH curve from each other.
[Relation between the drug-metabolizing activities of liver microsomes and multiplicity of cytochrome P-450 (author's transl)]. Wada et al. found a hyperbolic curve in the Lineweaver-Burk plots of the drug-metabolizing activity and competitive inhibition of steroid hormones to drugs, and suggested that several enzymes acting on different sites of various steroid hormone molecules might metabolize drugs without having specificities for hydroxylation sites. Recently, several cytochrome P-450s were separated and purified from liver microsomes. We studied the relation between the drug-metabolizing activities and multiplicity of cytochrome P-450 with the pH curve and the Lineweaver-Burk plots. Phenobarbital- and methylcholanthrene-treatment had remarkable effects on the pH curve of aniline hydroxylation by mouse liver microsomes. Addition of cortisol inhibited aniline hydroxylatin by liver microsomes from phenobarbital-treated mice more effectively at higher pH range and the pH curve was similar to that seen for normal mice. Haugen and Coon separated preparations [A] [B] and [C] with hydroxylapatite chromatography and we obtained [A'] (eluted by 100 mM K-phosphate buffer, pH 7.4) between [A] (50 mM) and [B] (300 mM). The preparation [A'] had the same absorption maximum (451 nm) of reduced CO complex as [A], but Km and pH curve for [A'] were similar to those for [B]. Each separated preparation of cytochrome P-450 showed a hyperbolic curve in Lineweaver-Burk plots and a different pH curve from each other.