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-448 1 and MC P-448 2) 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-448 1 and MC P-448 2 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-448 1 or MC P448 2. On the contrary, no inhibition of PB P-450 supported benzphetamine N-demethylation was observed when MC P-448 1 or MC P-448 2 was added to the system containing PB P-450 and limited amount of the reductase. The apparent K m 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-448 1 or MC P-448 2. These and other results suggest that there is a certain hierarchy among the cytochrome P-450 species for receiving electrons from reductase.