Melanin versus protein synthesis in melanocytes in vitro

Abstract

Melanin and protein synthesis in cultured mouse pigment cells (440W and 440B) were studied by autoradiography and scintillation counting. The non-pigmented 440W cells did not incorporate tyrosine in the presence of inhibitors of protein synthesis, e.g. cycloheximide or puromycin. However, the pigmented 440B cells incorporated tyrosine despite these inhibitors, at a linear rate up to 4 h. When phenylthiourea, an inhibitor of tyrosinase, was used, the incorporation of tyrosine was markedly reduced. DOPA incorporation also was reduced by phenylthiourea but not by cycloheximide or puromycin. Thus melanin synthesis was not inhibited by the inhibitors of protein synthesis. These findings suggest that cessation of protein synthesis does not, at the same time, affect tyrosinase activity. On the basis of these observations, we propose the scintillation counting of radioactive tyrosine incorporation as a quantitative assay method for melanin synthesis.