title: Oxidation products of quercetin catalyzed by mushroom tyrosinase.
abstract: Quercetin was oxidized as a substrate catalyzed by mushroom tyrosinase to the corresponding o-quinone and subsequent isomerization to p-quinone methide type intermediate; followed by the addition of water on C-2 yielding a relatively stable intermediate, 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone. In the presence of a catalytic amount of l-DOPA as a cofactor, the rate of this oxidation was enhanced. Fisetin, which lacks the C-5 hydroxyl group, was also oxidized but the rate of oxidation was faster than that of quercetin, indicating that the C-5 hydroxyl group is not essential but is associated with the activity.
authors.affiliation: Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720-3112, USA. ikubo@uclink.berkeley.edu
authors.forename: Isao
authors.initials: I
authors.lastname: Kubo
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Nihei
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Shimizu
mesh_terms: D000363:Agaricales / Q000201:enzymology*; D001572:Benzofurans / Q000032:analysis / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D007980:Levodopa / Q000494:pharmacology; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D011048:Polarography; D011794:Quercetin / Q000378:metabolism*; D011809:Quinones / Q000032:analysis* / Q000737:chemistry
chemical_list: D001572:Benzofurans; D011809:Quinones; D007980:Levodopa; D011794:Quercetin; D014442:Monophenol Monooxygenase