title: Reactions of Flavonoids with o-Quinones Interfere with the Spectrophotometric Assay of Tyrosinase Activity.
abstract: Flavonoids are important food components with antioxidant properties and many of them have been described as tyrosinase inhibitors. Oxidation of quercetin, kaempferol, morin, catechin, and naringenin by mushroom tyrosinase and their influence on the oxidation of l-dopa and l-tyrosine was studied. Reaction rates measured spectrophotometrically and by oxygen consumption differed substantially. All tested flavonoids reacted with 4-tert-butyl-o-benzoquinone and/or 4-methyl-o-benzoquinone, although at different rates. These reactions generated products whose UV-vis spectra either overlapped or did not overlap with the spectrum of dopachrome. They therefore strongly influence the kinetic analysis performed by measuring the absorbance at 475 nm during oxidation of l-dopa or l-tyrosine generating false inhibition or activation effects. This method is therefore inappropriate for monitoring the activity of this enzyme in the presence of flavonoids and other compounds possessing strong nucleophilic or reducing groups.
authors.affiliation: Faculty of Chemistry, Opole University , Ul. Oleska 48, 45-052 Opole, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Gąsowska-Bajger
authors.affiliation: Faculty of Chemistry, Opole University , Ul. Oleska 48, 45-052 Opole, Poland.
authors.forename: Hubert
authors.initials: H
authors.lastname: Wojtasek
mesh_terms: D000364:Agaricus / Q000201:enzymology; D016227:Benzoquinones / Q000737:chemistry*; D057075:Enzyme Assays; D005419:Flavonoids / Q000737:chemistry*; D005656:Fungal Proteins / Q000737:chemistry*; D007700:Kinetics; D014442:Monophenol Monooxygenase / Q000737:chemistry*; D010084:Oxidation-Reduction; D013053:Spectrophotometry / Q000379:methods*
chemical_list: D016227:Benzoquinones; D005419:Flavonoids; D005656:Fungal Proteins; C004532:quinone; D014442:Monophenol Monooxygenase
keywords: catechol; enzymatic assay interference; flavonoids; o-quinone; redox exchange; tyrosinase