title: A new monooxygenase product from 7-ethoxycoumarin and its relation to the O-dealkylation reaction.
abstract: The widely used fluorometric microsomal monooxygenase test for 7-ethoxycoumarin O-dealkylation was reinvestigated with regard to other possible hydroxylation products. By HPLC-analysis no beta-hydroxylation of the ethyl group and no 8-hydroxylation could be detected. Only a small percentage of 6-hydroxylation occurred, but as a new major metabolite 7-ethoxy-3-hydroxycoumarin was found in quantities depending on the microsomal preparation used. The ratio of O-dealkylation to 3-hydroxylation varied according to species, induction, buffer and pH, suggesting that different isozymes of cytochrome P450 were involved. The isozyme mainly responsible for 3-hydroxylation exhibited a great dependence on cytochrome b5 as the donor for the second electron. The fluorometric test does not include 3-hydroxylation due to the virtual absence of an emission spectrum above 450 nm.
mesh_terms: D015660:7-Alkoxycoumarin O-Dealkylase; D000818:Animals; D003374:Coumarins / Q000378:metabolism*; D003573:Cytochrome b Group / Q000096:biosynthesis / Q000378:metabolism; D015786:Cytochromes b5; D004790:Enzyme Induction / Q000187:drug effects; D006900:Hydroxylation; D007527:Isoenzymes / Q000096:biosynthesis / Q000378:metabolism; D051379:Mice; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000096:biosynthesis / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010105:Oxygenases / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013379:Substrate Specificity; D013552:Swine; D013997:Time Factors
chemical_list: D003374:Coumarins; D003573:Cytochrome b Group; D007527:Isoenzymes; D009243:NAD; C017299:7-ethoxycoumarin; D009249:NADP; D015786:Cytochromes b5; D006899:Mixed Function Oxygenases; D010105:Oxygenases; D015660:7-Alkoxycoumarin O-Dealkylase; D010634:Phenobarbital