title: Identification of the cytochrome P450 isoforms involved in the O-demethylation of 4-nitroanisole in human liver microsomes.
abstract: 1. 4-Nitroanisole is O-demethylated to 4-nitrophenol by human liver microsomes. Kinetic studies indicate that this metabolic route is mediated by two cytochrome P450 isoforms, one with a K(m) = 2.1 microM and the other with a K(m) = 220 microM. 2. Chemical inhibition and correlation studies in human liver microsomes indicate that the low K(m) enzyme is CYP2A6 and the high K(m) enzyme is CYP2E1 suggesting that44-nitroanisole is not a general cytochrome P450 substrate. 3. Studies using expressed recombinant cytochrome P450s indicated that all the cytochrome P450s investigated metabolized 4-nitroanisole but CYP2A6 and CYP2E1 produced the highest rates. Kinetic studies with these two isoforms produced a K(m) for CYP2A6 of 9 microM and 54 microM for CYP2E1. 4. The involvement of these two isoforms in the O-demethylation of 4-nitroanisole can be rationalized in terms of a hydrogen bond interaction with the nitro group and the active site of CYP2A6 and a hydrophobic interaction with the active site of CYP2E1.
authors.affiliation: Department of Drug Metabolism, Pfizer Central Research, Sandwich, UK.
authors.forename: B C
authors.initials: BC
authors.lastname: Jones
authors.forename: C A
authors.initials: CA
authors.lastname: Tyman
authors.forename: D A
authors.initials: DA
authors.lastname: Smith
mesh_terms: D000328:Adult; D000368:Aged; D000840:Anisoles / Q000378:metabolism*; D000890:Anti-Infective Agents / Q000494:pharmacology; D000925:Anticoagulants / Q000494:pharmacology; D000935:Antifungal Agents / Q000494:pharmacology; D000962:Antimalarials / Q000494:pharmacology; D001667:Binding, Competitive; D003374:Coumarins / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007654:Ketoconazole / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008745:Methylation; D008862:Microsomes, Liver / Q000201:enzymology*; D008875:Middle Aged; D011802:Quinidine / Q000494:pharmacology; D013379:Substrate Specificity; D013426:Sulfaphenazole / Q000494:pharmacology; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D000840:Anisoles; D000890:Anti-Infective Agents; D000925:Anticoagulants; D000935:Antifungal Agents; D000962:Antimalarials; D003374:Coumarins; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D013426:Sulfaphenazole; D003577:Cytochrome P-450 Enzyme System; C030123:coumarin; D013806:Theophylline; C050131:furafylline; C005306:4-nitroanisole; D011802:Quinidine; D007654:Ketoconazole