title: Effects of thymol on mushroom tyrosinase-catalyzed melanin formation.
abstract: The novel inhibitory mechanism of thymol (2-isopropyl-5-methylphenol) on dopachrome formation by mushroom tyrosinase (EC 1.14.18.1) was identified. The UV-vis spectrum and oxygen consumption assays showed dopachrome formation using L-tyrosine as a substrate was suppressed by thymol. This inhibitory activity was reversed by the addition of a well-known radical scavenger, butylated hydroxyanisole (BHA). Further investigations using N-acetyl-L-tyrosine as a substrate with HPLC analysis suggested that thymol inhibits chemical redox reactions between dopaquinone and leukodopachrome instead of enzymatic reaction. This redox inhibitory activity of thymol was examined by using a model redox reaction with L-dihydroxyphenylalanine (L-DOPA) and p-benzoquinone. Thymol successfully inhibited oxidation of L-DOPA to dopaquinone, coupled with reduction of p-benzoquinone. Hence, the suppression of dopachrome formation by thymol is due to the inhibition of conversion of leukodopachrome to dopachrome. The antioxidant property of thymol is a key characteristic for the inhibitory mechanism of melanin synthesis.
authors.affiliation: Department of Nutritional Science and Toxicology, University of California, Berkeley, California 94720, United States.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Satooka
authors.forename: Isao
authors.initials: I
authors.lastname: Kubo
mesh_terms: D000363:Agaricales / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015416:Maillard Reaction / Q000187:drug effects; D008543:Melanins / Q000096:biosynthesis*; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D013943:Thymol / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D008543:Melanins; D013943:Thymol; D014442:Monophenol Monooxygenase