%0 Journal Article %A ANTHONY Y. H. LU %A SUSAN B. WEST %T Reconstituted Liver Microsomal Enzyme System That Hydroxylates Drugs, Other Foreign Compounds, and Endogenous Substrates %B III. Properties of the Reconstituted 3,4-Benzpyrene Hydroxylase System %D 1972 %J Molecular Pharmacology %P 490-500 %V 8 %N 5 %X The hydroxylation of 3,4-benzpyrene by the reconstituted liver microsomal system from rats treated with 3-methylcholanthrene required cytochrome P-448, NADPH-dependent reductase, and lipid for maximal activity. Synthetic phosphatidylcholine could replace the lipid fraction. while detergents such as Triton X-100, sodium deoxycholate, and sodium cholate could only partially replace the lipid fraction. The apparent Km values of NADPH and NADPH were 7.04 µM and 362 µM, respectively. The apparent Km of 3,4-benzpyrene was 1.53 µM for the reconstituted system from rats treated with phenobarbital and 2.87 µM for the reconstituted system from rats treated with 3-methylcholanthrene. Although the source of the reductase preparation (from either 3-methylcholanthrene- or phenobarbital-treated rats) did not appear to affect the Km of 3,4-benzpyrene in the cytochrome P-450-dependent system, the Km of 3,4-benzpyrene in the cytochrome P-448-dependent system was significantly increased when the reductase from 3-methylcholanthrene-treated rats was replaced with the reductase from rats treated with phenobarbital. In contrast, the lipid fractions from phenobarbital- and 3-methylcholanthrene-treated rats were interchangeable, and thus the source of lipid did not affect the Km of 3,4-benzpyrene in either of the reconstituted systems. The cytochrome P-450 fractions from rats treated with phenobarbital was only 10% as active as the cytochrome P-448 fraction in catalyzing the hydroxylation of 3,4-benzpyrene in the presence of reductase and lipid. Cytochrome P-448- and P-450-dependent 3,4-benzpyrene hydroxylations could be selectively affected by various compounds, which suggests— along with other indirect evidence—that the low activity with cytochrome P-450 for 3,4-benzpyrene hydroxylation is due to an inherent property of cytochrome P-450 and is not due to contamination of the cytochrome P-450 preparation with cytochrome P-448. ACKNOWLEDGMENTS The authors are grateful to Drs. R. Kuntzman and A. H. Conney for their helpful criticism during the course of this work. We also wish to thank Mrs. Mary Ann Sadvary for preparing the manuscript. %U https://molpharm.aspetjournals.org/content/molpharm/8/5/490.full.pdf