A high spin form of cytochrome P-448 highly purified from PCB-treated rats--II. Characteristic requirement of cytochrome b5 for maximum activity.
A high spin form of cytochrome P-448 (PCB P-448-H), highly purified from microsomes of PCB-treated rats, catalyzed oxidations of several compounds and required cytochrome b5 for its full activities in all oxidations examined. PCB P-448-H catalyzed the hydroxylation of aniline and O-dealkylations of p-alkoxy derivatives of aniline and nitrobenzene and 7-alkoxy derivatives of coumarin. Among the activities measured, hydroxylation of aniline and O-dealkylation of p-alkoxy derivatives of aniline were catalyzed by PCB P-448-H more efficiently than by PCB P-448-L, which was a low spin form of cytochrome P-448 purified from liver microsomes of PCB-treated rats. In all reactions, PCB P-448-H required cytochrome b5 for maximum activity. Slight requirements were also seen with PCB P-448-L but varied equivocally depending on the substrates. Cytochrome b5 showed its maximum effects on p-propoxyaniline O-depropylation activity at a molar ratio of cytochrome b5 to PCB P-448-H of 1:2. The enhancement by cytochrome b5 was more pronounced when lower concentrations of either the substrate or NADPH-cytochrome P-450 reductase were added to the reconstituted system. Based on these results, we confirm that PCB P-448-H is a unique form of cytochrome P-448 with respect to the requirements for cytochrome b5 and is a good probe to study the mechanisms involved in the enhancement of drug oxidations by cytochrome b5.
D000818:Animals; D019388:Cytochrome P-450 CYP1A2; D003573:Cytochrome b Group / Q000378:metabolism*; D003580:Cytochromes / Q000302:isolation & purification / Q000378:metabolism*; D015786:Cytochromes b5; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010634:Phenobarbital / Q000494:pharmacology; D011078:Polychlorinated Biphenyls / Q000494:pharmacology*; D051381:Rats; D013379:Substrate Specificity
D003573:Cytochrome b Group; D003580:Cytochromes; D015786:Cytochromes b5; D011078:Polychlorinated Biphenyls; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; D009251:NADPH-Ferrihemoprotein Reductase; D010634:Phenobarbital