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  • Title: Evidence for covalent lipoyl adduction with dopaquinone following tyrosinase-catalyzed oxidation.
    Author: Tsuji-Naito K, Hatani T, Okada T, Tehara T.
    Journal: Biochem Biophys Res Commun; 2006 Apr 28; 343(1):15-20. PubMed ID: 16527255.
    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.
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