title: CO binding kinetics of human cytochrome P450 3A4. Specific interaction of substrates with kinetically distinguishable conformers.
abstract: The kinetics of CO binding to human cytochrome P450 3A4 was examined by the flash photolysis technique, employing the membrane-bound P450 expressed in baculovirus-infected SF9 insect cells. Triexponential kinetics was observed, indicating that P450 3A4 is composed of multiple, kinetically distinguishable conformers. To define the substrate specificity of individual P450 3A4 conformers we evaluated the effect of a series of substrates of varying sizes and structures on the CO binding kinetics. The rate of CO binding to the total mixture of P450 3A4 conformers was increased in the presence of nifedipine and erythromycin, decreased by quinidine, testosterone, and warfarin, and unaffected by cimetidine and 17 alpha-ethynylestradiol. A recently developed kinetic difference method (Koley, A. P., Robinson, R. C., Markowitz, A., and Friedman, F. K. (1994) Biochemistry 33, 2484-2489) was used to define the kinetic parameters of individual P450 3A4 conformers. The results showed that different conformers have distinct substrate specificities. The substrates had markedly variable effects on the CO binding kinetics of their target P450 3A4 conformers and thus differentially modulate their conformations. These results demonstrate that the interaction of a particular substrate with a specific P450 3A4 conformer can be assessed in the presence of multiple conformers.
authors.affiliation: Laboratory of Molecular Carcinogenesis, NCI National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: A P
authors.initials: AP
authors.lastname: Koley
authors.forename: J T
authors.initials: JT
authors.lastname: Buters
authors.forename: R C
authors.initials: RC
authors.lastname: Robinson
authors.forename: A
authors.initials: A
authors.lastname: Markowitz
authors.forename: F K
authors.initials: FK
authors.lastname: Friedman
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism*; D002927:Cimetidine / Q000494:pharmacology; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D004917:Erythromycin / Q000494:pharmacology; D004997:Ethinyl Estradiol / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000096:biosynthesis / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D011485:Protein Binding; D011802:Quinidine / Q000494:pharmacology; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D018411:Spodoptera; D013379:Substrate Specificity; D013739:Testosterone / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014859:Warfarin / Q000494:pharmacology
chemical_list: D011994:Recombinant Proteins; D013739:Testosterone; D004997:Ethinyl Estradiol; D014859:Warfarin; D004917:Erythromycin; D002248:Carbon Monoxide; D002927:Cimetidine; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; D009543:Nifedipine; D011802:Quinidine