Inhibitory Effects on L-Dopa Oxidation of Tyrosinase by Skin-whitening Agents

Abstract

Tyrosinase (EC 1.14.18.1) is a copper-containing monooxygenase catalyzing the o-hydroxylation of monophenols to the corresponding catechols (monophenolase or cresolase activity), and the oxidation of monophenols to the corresponding o-quinones (diphenolase or catecholase activity). These functions of tyrosinase play an important role in the formation of melanin pigments during melanogenesis. Melanin production is principally responsible for skin color and plays an important role in prevention of sun-induced skin injury. However, abnormal accumulation of melanin products is responsible for hyperpigmentations including melasma, freckles, and senile lentigines, which could be a serious aesthetic problem. Recently, a global market demand has developed for skinwhitening agents because some dark-skinned individuals in many countries and races are prefer lighter skin color. Several tyrosinase inhibitors have been used in the cosmetic industry as skin-whitening agents. Unfortunately, many of these inhibitors have not been demonstrated yet to be clinically efficacious when critically analyzed in carefully controlled studies. Thus, many efforts are still devoted to screening recognized and putative skin-whitening agents. A correct assay method is essential for the development of effective inhibitors of tyrosinase. Until now, the screening and evaluation methods of these skin-whitening agents have been adopted dopa oxidation test by mushroom tyrosinase because of its commercial availability, not human tyrosinase. Moreover, a comparative study on the inhibitory effects of skin-whitening agents by human tyrosinase and mushroom tyrosinase is still undone. In this study, we investigated inhibitory effects of skinwhitening agents on L-dopa oxidation by human tyrosinase and mushroom tyrosinase, and compared their effects. According to our study described here, L-dopa oxidation activities of human tyrosinase and mushroom tyrosinase show very different inhibitory effects depending upon the nature of skin-whitening agents.