Dopachrome oxidoreductase: a new enzyme in the pigment pathway

We report our preliminary characterization of a new enzyme in the pigment pathway which we propose to call dopachrome oxidoreductase (DCOR). This enzyme, prepared from mouse melanoma, catalyzed the conversion of dopachrome to 5,6-dihydroxyindole and also appeared to block the pigment pathway at this latter compound in the absence of tyrosinase. DCOR was protease-sensitive, heat-labile, and showed maximum stability in the range of pH 6-8. The molecular weight of DCOR was estimated to be 34,000 by gel filtration. DCOR had a subcellular distribution within the melanocyte which was similar to that of tyrosinase, but DCOR activity was found in melanocytes devoid of tyrosinase activity and was not inhibited by tyrosinase inhibitors. DCOR may prove to be an active regulatory enzyme in melanogenesis.