title: Diversity in mechanisms of substrate oxidation by cytochrome P450 2D6. Lack of an allosteric role of NADPH-cytochrome P450 reductase in catalytic regioselectivity.
abstract: Cytochrome P450 (P450) 2D6 was first identified as the polymorphic human debrisoquine hydroxylase and subsequently shown to catalyze the oxidation of a variety of drugs containing a basic nitrogen. Differences in the regioselectivity of oxidation products formed in systems containing NADPH-P450 reductase/NADPH and the model oxidant cumene hydroperoxide have been proposed by others to be due to an allosteric influence of the reductase on P450 2D6 (Modi, S., Gilham, D. E., Sutcliffe, M. J., Lian, L.-Y., Primrose, W. U., Wolf, C. R., and Roberts, G. C. K. (1997) Biochemistry 36, 4461-4470). We examined the differences in the formation of oxidation products of N-methyl-4-phenyl-1,2,5,6-tetrahydropyridine, metoprolol, and bufuralol between reductase-, cumene hydroperoxide-, and iodosylbenzene-supported systems. Catalytic regioselectivity was not influenced by the presence of the reductase in any of the systems supported by model oxidants, ruling out allosteric influences. The presence of the reductase had little effect on the affinity of P450 2D6 for any of these three substrates. The addition of the reaction remnants of the model oxidants (cumyl alcohol and iodobenzene) to the reductase-supported system did not affect reaction patterns, arguing against steric influences of these products on catalytic regioselectivity. Label from H(2)18O was quantitatively incorporated into 1'-hydroxybufuralol in the iodosylbenzene- but not in the reductase- or cumene hydroperoxide-supported reactions. We conclude that the P450 systems utilizing NADPH-P450 reductase, cumene hydroperoxide, and iodosylbenzene use similar but distinct chemical mechanisms. These differences are the basis for the variable product distributions, not an allosteric influence of the reductase.
authors.affiliation: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, 23rd and Pierce Avenues, Nashville, TN 37232-0146, USA.
authors.forename: I H
authors.initials: IH
authors.lastname: Hanna
authors.forename: J A
authors.initials: JA
authors.lastname: Krauser
authors.forename: H
authors.initials: H
authors.lastname: Cai
authors.forename: M S
authors.initials: MS
authors.lastname: Kim
authors.forename: F P
authors.initials: FP
authors.lastname: Guengerich
mesh_terms: D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000378:metabolism; D000319:Adrenergic beta-Antagonists / Q000378:metabolism; D000494:Allosteric Regulation; D019388:Cytochrome P-450 CYP1A2 / Q000378:metabolism; D019389:Cytochrome P-450 CYP2D6 / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D015259:Dopamine Agents / Q000378:metabolism; D004983:Ethanolamines / Q000378:metabolism; D008790:Metoprolol / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000378:metabolism; D008956:Models, Chemical; D008968:Molecular Conformation; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D015259:Dopamine Agents; D004983:Ethanolamines; C010831:bufuralol; D003577:Cytochrome P-450 Enzyme System; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D019388:Cytochrome P-450 CYP1A2; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; D009251:NADPH-Ferrihemoprotein Reductase; D008790:Metoprolol