Purification and properties of cytochrome P-450 and NADPH-cytochrome c (P-450) reductase from human liver microsomes.

Cytochrome P-450 and NADPH-cytochrome c (P-450) reductase were purified to 10.6 nmoles per mg of protein and 19.9 units per mg of protein, respectively, from human liver microsomes. The purified cytochrome was assumed to be in a low spin state as judged by the absolute spectrum. n-Octylamine and aniline produced type II difference spectra and SKF 525-A and benzphetamine type I spectra when bound to the purified cytochrome P-450. The purified human cytochrome P-450 catalyzed laurate oxidation as determined by NADPH oxidation but not aniline hydroxylation, benzphetamine N-demethylation and 7-ethoxycoumarin O-deethylation when reconstituted with the reductases purified from human and rat liver microsomes. The human cytochrome P-450, however, catalyzed drug oxidations when cumene hydroperoxide was used as the oxygen source. The purified human NADPH-cytochrome c (P-450) reductase contained FAD and FMN at a ratio of 1:0.76. The reductase was capable of supporting 7-ethoxycoumarin O-deethylation activity of cytochrome P-448 purified from 3-methylcholanthrene-treated rat liver microsomes.