RT Journal Article SR Electronic T1 Enhancement of Cytochrome P-450 3A4 Catalytic Activities by Cytochrome b 5 in Bacterial Membranes JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 999 OP 1004 VO 27 IS 9 A1 Hiroshi Yamazaki A1 Miki Nakajima A1 Mami Nakamura A1 Satoru Asahi A1 Noriaki Shimada A1 Elizabeth M. J. Gillam A1 F. Peter Guengerich A1 Tsutomu Shimada A1 Tsuyoshi Yokoi YR 1999 UL http://dmd.aspetjournals.org/content/27/9/999.abstract AB Activities of testosterone, nifedipine, and midazolam oxidation by recombinant cytochrome P-450 (P-450) 3A4 coexpressed with human NADPH-P-450 reductase (NPR) in bacterial membranes (CYP3A4/NPR membranes) were determined in comparison with those of other recombinant systems and of human liver microsomes with high contents of CYP3A4. Growth conditions for Escherichia colitransformed with the bicistronic construct affected expression levels of CYP3A4 and NPR; an excess of NPR over P-450 in membrane preparations enhanced CYP3A4-dependent testosterone 6β-hydroxylation activities of the CYP3A4/NPR membranes. Cytochrome b5(b5) and apolipoproteinb5 further enhanced the testosterone 6β-hydroxylation activities of CYP3A4/NPR membranes after addition to either bacterial membranes or purified enzymes. NPR was observed to enhance catalytic activity when added to the CYP3A4/NPR membranes, either in the form of bacterial membranes or as purified NPR (in combination with cholate and b5). Apparent maximal activities of testosterone 6β-hydroxylation in CYP3A4/NPR membranes were obtained when the molar ratio of CYP3A4/NPR/b5 was adjusted to 1:2:1 by mixing membranes containing each protein. Testosterone 6β-hydroxylation, nifedipine oxidation, and midazolam 4- and 1′-hydroxylation activities in CYP3A4/NPR membranes plusb5 systems were similar to those measured with microsomes of insect cells coexpressing CYP3A4 with NPR and/or of human liver microsomes, based on equivalent CYP3A4 contents. These results suggest that CYP3A4/NPR membrane systems containingb5 are very useful models for prediction of the rates for liver microsomal CYP3A4-dependent drug oxidations. The American Society for Pharmacology and Experimental Therapeutics