Journal article
CYP2C9 protein interactions with cytochrome b5: Effects on the coupling of catalysis
Drug metabolism and disposition, Vol.35(7), pp.1174-1181
07/2007
Handle:
https://hdl.handle.net/2376/114665
PMCID: PMC2386961
PMID: 17446262
Abstract
The hemoprotein cytochrome b5 (cyt b5) has been demonstrated to affect the kinetics of drug oxidation by the microsomal cytochromes P450. However, the mechanisms through which cyt b5 exerts these effects are variable and P450 isoform-dependent. While the effects of cyt b5 on the major drug metabolizing enzymes CYP2D6, CYP2E1, and CYP3A4 are well studied, fewer studies conducted over limited ranges of cyt b5 concentrations have been performed on CYP2C9. In the present study with CYP2C9, cyt b5 exerted complex actions upon P450 oxidative reactions by affecting the rate of metabolite formation, the consumption of NADPH by cytochrome P450 reductase, and uncoupling of the reaction cycle to hydrogen peroxide and water. Cytochrome b5 devoid of the heme moiety (apo-b5) exhibited similar effects as native cyt b5. All rates were highly dependent on the cyt b5 to CYP2C9 enzyme ratio suggesting that the amount of cyt b5 present in an
in vitro
incubation is an important factor that can impact the reliability of extrapolating
in vitro
generated data to predict the
in vivo
condition. The major effects of cyt b5 are hypothesized to result from a cyt b5 induced conformational change in CYP2C9 that results in an increased collision frequency between the iron-oxygen species (Cpd I) and the substrate, and a decrease in the oxidase activity. Together, these findings suggest that cyt b5 can alter multiple steps in the P450 catalytic cycle via complex interactions with P450 and P450 reductase.
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Details
- Title
- CYP2C9 protein interactions with cytochrome b5: Effects on the coupling of catalysis
- Creators
- Charles W Locuson - Department of Experimental and Clinical Pharmacology, College of Pharmacy, University of Minnesota, Minneapolis, MNLarry C Wienkers - Department of Pharmacokinetics and Drug Metabolism, Amgen, Inc, Seattle, WAJeffrey P Jones - Department of Chemistry and Program in Physical Biosciences, Washington State University, Pullman, WATimothy S Tracy - Department of Experimental and Clinical Pharmacology, College of Pharmacy, University of Minnesota, Minneapolis, MN
- Publication Details
- Drug metabolism and disposition, Vol.35(7), pp.1174-1181
- Academic Unit
- Chemistry, Department of
- Identifiers
- 99900548467601842
- Language
- English
- Resource Type
- Journal article