Characterization of partially purified cytochromes P-450 and P-448 from rat liver microsomes.

The liver microsomal hydroxylation enzyme system has been resolved into three components: cytochrome P-450, an NADPH-dependent reductase, and a lipid identified as phosphatidylcholine (1, 2). Using the reconstituted hydroxylation system, we have recently shown that the enzyme systems prepared from PB-’ or 3-MCtreated immature, male rats exhibit different substrate specificities and that such specificities reside primarily in the cytochrome fraction, rather than in the reductase or lipid fraction (3, 4). It was concluded from these studies that the cytochrome P.450 fraction from rats treated with PB is catalytically different from the cytochrome P448’ fraction from rats treated with 3-MC. We have recently further purified the hemoprotein fractions from untreated (control-P-450), PB-treated (PB-P-450), and 3-MC-treated (P448) immature, male rats (8), and this paper will deal with some of the properties of these partially purified preparations. A number of other laboratories have also solubilized and, in some cases, partially purified liver microsomal cytochromes P-450 and P-448 (1, 9-12).