title: Evidence for covalent lipoyl adduction with dopaquinone following tyrosinase-catalyzed oxidation.
abstract: Previous studies have examined the conjugation of sulfhydryl compounds such as L-cysteine and glutathione with DOPA-quinone following the oxidation of tyrosine and DOPA by tyrosinase. These covalent reactions play a key role in the regulation and metabolism of pigment cells. We report on the first direct evidence for the formation of lipoyl adducts in reactions of thiol groups with DOPA-quinone in dihydrolipoic acid (6,8-dimercaptooctanoic acid [DHLA]). Incubating DHLA with DOPA-quinone followed by tyrosinase-catalyzed oxidation resulted in the three products predicted by HPLC-UV and LC-ESI(-)-MS analyses for DHLA DOPA conjugates. In the current study, we identified 5-S-lipoyl-DOPA among the principal products isolated by HPLC and characterized by FAB(-)-MS, ESI(-)-MS/MS, and 1H NMR, 2D-COSY studies. Collectively, these results suggest that DHLA undergoes sulfhydryl conjugation with DOPA-quinone, pointing to the involvement of thiol-reactive metabolites.
authors.affiliation: DHC Corporation Laboratories, Division 2, 2-24 Hamada, Mihama-ku, Chiba 261-0025, Japan. knaito@dhc.co.jp
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tsuji-Naito
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hatani
authors.forename: Takeshi
authors.initials: T
authors.lastname: Okada
authors.forename: Takao
authors.initials: T
authors.lastname: Tehara
mesh_terms: D016227:Benzoquinones / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D014442:Monophenol Monooxygenase / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry
chemical_list: C510391:5-lipoyl-DOPA; D016227:Benzoquinones; D004295:Dihydroxyphenylalanine; D008063:Thioctic Acid; C015144:dihydrolipoic acid; C035157:dopaquinone; D014442:Monophenol Monooxygenase