We have studied the inhibitory effects of 4-n-butyl-resorcinol (4BR) on the activity of isolated tyrosinase and on melanogenesis in cultured B16 melanoma cells. 4BR inhibited the activity of all the isolated tyrosinases from mushrooms, B16 melanoma cells and brownish guinea pig skin. The inhibitory concentration (IC50) of 4BR for tyrosinase from B16 melanoma cells was 8.0 10 -6 M. Linewever-Burk plot analysis showed that 4BR competitively inhibited the activity of isolated tyrosinase from B16 melanoma cells. The inhibitory effect on melanogeneis was further studied in cultured B16 melanoma cells. 4BR decreased the amount of melanin per cell to 42% at the concentration of 1.0 10 -5 M, without any effects on cell growth, DNA synthesis and protein synthesis. The tyrosinase activity of in situ was also reduced to 45%. That the amounts of both T1 and T3 isozymes decreased was shown by the gel electrophoresis analysis. From these results, it is suggested that the inhibitory effects of 4BR on melanogenesis in cultured B16 melanoma cells are due to the direct inhibition of tyrosinase activity as well as the suppression of tyrosinase synthesis.
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