Abstract
Human hepatic cytochromes P450 (CYP) are integral to xenobiotic metabolism. CYP2B6 is a major catalyst of biotransformation of environmental toxicants, including polybrominated diphenyl ethers (PBDEs). CYP2B substrates tend to contain halogen atoms, but the biochemical basis for this selectivity and for species specific determinants of metabolism has not been identified. Spectral binding titrations and inhibition studies were performed to investigate interactions of rat CYP2B1, rabbit CYP2B4, and CYP2B6 with a series of phenoxyaniline (POA) congeners that are analogues of PBDEs. For most congeners, there was a <3-fold difference between the spectral binding constants (KS) and IC50 values. In contrast, large discrepancies between these values were observed for POA and 3-chloro-4-phenoxyaniline. CYP2B1 was the enzyme most sensitive to POA congeners, so the Val-363 residue from that enzyme was introduced into CYP2B4 or CYP2B6. This substitution partially altered the protein-ligand interaction profiles to make them more similar to that of CYP2B1. Addition of cytochrome P450 oxidoreductase (POR) to titrations of CYP2B6 with POA or 2'4'5'TCPOA decreased the affinity of both ligands for the enzyme. Addition of cytochrome b5 to a recombinant enzyme system containing POR and CYP2B6 increased the POA IC50 value and decreased the 2'4'5'TCPOA IC50 value. Overall, the inconsistency between KS and IC50 values for POA versus 2'4'5'TCPOA is largely due to the effects of redox partner binding. These results provide insight into the biochemical basis of binding of diphenyl ethers to human CYP2B6 and changes in CYP2B6-mediated metabolism that are dependent on POA congener and redox partner identity.
Publication types
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Comparative Study
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Research Support, N.I.H., Extramural
MeSH terms
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Alkylation / drug effects
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Amino Acid Substitution
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Aniline Compounds
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Animals
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Aryl Hydrocarbon Hydroxylases / antagonists & inhibitors*
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Aryl Hydrocarbon Hydroxylases / chemistry
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Aryl Hydrocarbon Hydroxylases / genetics
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Aryl Hydrocarbon Hydroxylases / metabolism
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Benzene Derivatives / pharmacology
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Cytochrome P-450 CYP2B1 / antagonists & inhibitors*
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Cytochrome P-450 CYP2B1 / chemistry
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Cytochrome P-450 CYP2B1 / genetics
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Cytochrome P-450 CYP2B1 / metabolism
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Cytochrome P-450 CYP2B6 / chemistry
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Cytochrome P-450 CYP2B6 / drug effects*
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Cytochrome P-450 CYP2B6 / genetics
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Cytochrome P-450 CYP2B6 / metabolism
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Cytochrome P-450 CYP2B6 Inhibitors / metabolism
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Cytochrome P-450 CYP2B6 Inhibitors / pharmacology
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Cytochrome P-450 Enzyme Inhibitors / metabolism
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Cytochrome P-450 Enzyme Inhibitors / pharmacology*
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Cytochrome P450 Family 2 / antagonists & inhibitors
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Cytochrome P450 Family 2 / chemistry
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Cytochrome P450 Family 2 / genetics
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Cytochrome P450 Family 2 / metabolism
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Cytochromes b5 / metabolism
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Environmental Pollutants / metabolism
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Halogenated Diphenyl Ethers / metabolism
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Halogenated Diphenyl Ethers / pharmacology*
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Humans
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Hydrocarbons, Halogenated / metabolism
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Inhibitory Concentration 50
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Molecular Structure
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Mutagenesis, Site-Directed
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NADPH Oxidases / metabolism
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Oxidation-Reduction
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Rabbits
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Rats
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Recombinant Proteins / metabolism
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Structure-Activity Relationship
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Substrate Specificity
Substances
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Aniline Compounds
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Benzene Derivatives
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Cytochrome P-450 CYP2B6 Inhibitors
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Cytochrome P-450 Enzyme Inhibitors
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Environmental Pollutants
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Halogenated Diphenyl Ethers
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Hydrocarbons, Halogenated
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Recombinant Proteins
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Cytochromes b5
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Aryl Hydrocarbon Hydroxylases
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CYP2B6 protein, human
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Cytochrome P-450 CYP2B1
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Cytochrome P-450 CYP2B6
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Cytochrome P450 Family 2
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cytochrome P-450 CYP2B4 (rabbit)
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NADPH Oxidases
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cumene hydroperoxide