HYDROGEN-PEROXIDE AS A MEDIATOR OF DOPAC-INDUCED EFFECTS ON MELANOMA-CELLS

Dopac increases tyrosinase activity and exerts cytotoxic effects in cultures of human melanoma cells. The possible role of hydrogen peroxide in these actions was examined. Catalase (100-mu-g/ml) completely reversed the cytotoxic action of 0.3 mM dopac and reduced its tyrosinase-stimulating effect by approximately one half. The results show that extracellular hydrogen peroxide is a mediator of both the tyrosinase-stimulating and cytotoxic actions of dopac. Analysis of the degradation products of melanin from dopac-treated melanoma cells after hydriodic acid (HI) hydrolysis revealed the presence of aminohydroxy-phenylacetic acid (AHPAc). This substance is obtained by HI hydrolysis of melanin formed by oxidation of cysteinyl-dopac. Thus, the presence of AHPAc indicates that dopac is transported into the melanocytes where it serves s a substrate for tyrosinase.