Biol. Pharm. Bull. 28(2) 323—327 (2005)

gen oxidoreductase, EC 1.14.18.1) is a copper-dependent protein widely distributed in nature. The enzyme catalyzes two different reactions: the hydroxylation of monophenols to o-diphenols (monophenolase activity) and the oxidation of odiphenols to o-quinones (diphenolase activity), both utilizing molecular oxygen. The enzymatic browning of fruits and vegetables is mostly related to the oxidation of endogenous phenolic containing compounds catalyzed by polyphenol oxidase. Tyrosinase also is responsible for melanization in animals, and is the key enzyme for the regulation of melanogenesis in mammals. Melanin is synthesized in epidermal melanocytes, and then is transferred into epidermal keratinocytes via the melanocytes’ dendrites. Melanogenesis is the process by which melanin is produced (and subsequently distributed) by melanocytes within the skin and hair follicles. This process results in the synthesis of melanin pigments, which plays a protective role against skin photocarsinogenesis. The main physiological stimulus of melanogenesis is the ultraviolet radiation of solar light, which can act directly on melanocytes or indirectly through the release of keratinocyte-derived factors such as MSH (a-melanocyte stimulating hormone). One of the biggest causative agents of hyperpigmentaion is probably UV light. However, skin darkening can be suppressed, at least partially, by deactivating of tyrosinase. Therefore, tyrosinase inhibitors have become increasingly important in the cosmetic and medicinal products used in the prevention of hyperpigmentaion. Many compounds, such as hydroquinone, kojic acid, and benzaldehyde-O-alkyloximes have been reported as tyrosinase inhibitors. The established murine B16F10 melanoma cell (B16 cells) line offers a model system with readily quantifiable markers that are characteristic of differentiating, including melanogenesis. In B16 cells, a-tocopheryl ferulate was shown to have depigmenting effect. Although 4,4 -dihydroxybiphenyl (44 -BP), a bisphenol derivative was known as a radical scavenger for methacrylate polymerization, but its efficacy on tyrosinase inhibition and melanin biosynthesis has not been reported. The aim of this study was to characterize inhibition mode of 44 -BP on mushroom tyrosinase. We also examined the inhibitory effect of 44 -BP on melanin biosynthesis, and cell viability in B16 cells as a biomarker for the potential cytotoxicity.