title: The interaction between two forms of cytochrome P-450 during drug oxidation in the reconstituted system containing limited amount of NADPH-cytochrome P-450 reductase.
abstract: The activities of drug oxidation in a reconstituted system which contains two forms of cytochrome P-450 and a limiting amount of NADPH-cytochrome P-450 reductase were determined. Cytochrome P-450 (termed MC P-4481 and MC P-4482) purified from liver microsomes of 3-methyl-cholanthrene-treated rats was active in both 2- and 4-hydroxylation of biphenyl but cytochrome P-450 (termed PB P-450) purified from liver microsomes of phenobarbital-treated rats was active in 4-hydroxylation of biphenyl only. PB P-450, MC P-4481 and MC P-4482 were most active toward benzphetamine N-demethylation, aniline hydroxylation and 7-ethoxycoumarin O-deethylation, respectively. PB P-450 inhibited the activity of biphenyl 2-hydroxylation supported by MC P-4481 or MC P-4482. On the contrary, no inhibition of PB P-450 supported benzphetamine N-demethylation was observed when MC P-4481 or MC P-4482 was added to the system containing PB P-450 and limited amount of the reductase. The apparent Km of PB P-450 for the reductase obtained from double reciprocal plot of the reductase concentration and the activity of biphenyl hydroxylase or benzphetamine N-demethylation was lower than that of MC P-4481 or MC P-4482. These and other results suggest that there is a certain hierarchy among the cytochrome P-450 species for receiving electrons from reductase.
mesh_terms: D000818:Animals; D001713:Biphenyl Compounds / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis*; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D009251:NADPH-Ferrihemoprotein Reductase / Q000032:analysis*; D004364:Pharmaceutical Preparations / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001713:Biphenyl Compounds; D004364:Pharmaceutical Preparations; D003577:Cytochrome P-450 Enzyme System; D009251:NADPH-Ferrihemoprotein Reductase