Stimulation of microsomal drug oxidation activities by incorporation into microsomes of purified NADPH-cytochrome c (P-450) reductase.

Abstract

The effects of addition of purified NADPH-cytochrome c (P-450) reductase on hepatic microsomal activities of aniline hydroxylation, p-phenetidine 0-deethylation and ethylmorphine and aminopyrine N-demethylations were studied using microsomes from untreated, phenobarbital-treated and 3-methylcholanthrene-treated rats. The purified reductase was incorporated into microsomes. The drug oxidation activities were increased by the fortification of microsomes with the reductase while the extent of increase in the activities varied with the substrate and microsomes employed. The most pronounced enhancement was seen in p-phenetidine 0-deethylation, followed by aniline hydroxylation and aminopyrine and ethylmorphine N-demethylations. The enhancement was more remarkable in microsomes from rats treated with 3-methylcholanthrene or phenobarbital. .alpha.-Naphthoflavone inhibited p-phenetidine 0-deethylation activity markedly when the reductase was incorporated into microsomes, indicating that a larger amount of a species of cytochrome P-450 sensitive to the inhibitor was capable of participating in the oxidation of this substrate in the presence of the added reductase. One of the 2 Km values seen with higher concentrations of aniline or aminopyrine was altered by the fortification of microsomes with the purified NADPH cytochrome c (P-450) reductase. NADPH-cytochrome c (P-450) reductase transfers electrons to the selected 1 or 2 of multiple species of cytochrome P-450 preferentially depending upon the substrate and the concentration of the substrate in microsomal membranes.