Correlation between Changes in Enzymatic Activities and Induction of Different Forms of Rat Liver Microsomal Cytochrome P‐450 after Phenobarbital‐, 3‐Methylcholanthrene‐ and 16α‐Cyanopregnenolone Treatment

Multiple forms of liver microsomal cytochrome P-450 in rats were identified on SDS-polyacrylamide gels stained for protein and peroxidase activity after induction with phenobarbital, 3-methylcholanthrene, and 16α-cyanopregnenolone. The induced forms were correlated to the in vitro metabolism of biphenyl, benzo(a)pyrene and the steroids 4-androstene-3,17-dione and 5α-androstane-3α,17β-diol. Induction of two forms with apparent molecular weights of 54,000 (RLvMc P-450₅₄) and 50,000 (RLvMc P-450₅₀) was obtained with phenobarbital, induction of RLvMc P-450₅₅ and RLvMc P-450₅₈ with 3-methylcholanthrene and induction of RLvMc P-450₅₄ with 16α-cyanopregnenolone. The RLvMc P-450₅₀ was mainly associated with the formation of benzo(a)pyrene-4,5-dihydrodiol, and 7α-hydroxy-4-androstene-3,17-dione. The RLvMc P-450₅₅ and/or the RLvMc P-450₅₈ was mainly associated with the formation of 2- and 3-hydroxybiphenyl and benzo(a)pyrene-7,8-dihydrodiol and RLvMc P-450₅₄ was to some extent associated with the formation of benzo(a)pyrene-4,5-dihydrodiol and several metabolites of 5α-androstane-3α,17β-diol. It is suggested that SDS-polyacrylamide gel electrophoresis may be a valuable complement to enzyme assays in evaluating effects of drugs and environmental chemicals on the liver microsomal hydroxylase system.