THIOREDOXIN REDUCTASE INDUCTION COINCIDES WITH MELANIN BIOSYNTHESIS IN BROWN AND BLACK GUINEA-PIGS AND IN MURINE MELANOMA-CELLS

X-rays were used to induce melanin biosynthesis in brown and black gui nea pigs in vivo. During the course of pigmentation, the expression of thioredoxin reductase was increased, whereas for the other antioxidan t enzymes, superoxide dismutase (cytosol Cu/Zn-enzyme), catalase, and glutathione reductase, levels and activities decreased. Isobutylmethyl xanthine induced eumelanin biosynthesis in murine melanoma cells (clou dman S-91). In these cells, thioredoxin reductase levels coincided wit h melanogenesis. Our results suggest that both tyrosinase and thioredo xin reductase respond to oxidative stress in the epidermis as well as in melanoma cells and react with superoxide anion radicals to stimulat e melanogenesis and to prevent perioxidative damage, respectively.