The action of glycosylases on dopachrome (2-carboxy-2,3-dihydroindole-5,6-quinone) tautomerase

Abstract

It is shown that dopachrome (2-carboxy-2,3-dihydroindole-5,6-quinone) tautomerase (DCT) is a glycoprotein containing N-linked oligosaccharides. The enzymic activity can be stimulated by partial deglycosylation with a number of glycosylases such as neuraminidase, beta-mannosidase and beta-galactosidase. However, the stability of the enzyme after the hydrolytic treatment becomes lower. Thus total deglycosylation with peptide N-glycosidase F directly provokes an inactivation of DCT. The native enzyme also shows a strong affinity for concanavalin A-Sepharose. This affinity decreases after treatment with neuraminidase and/or beta-mannosidase. The DCT associated with coated vesicles seems to be mostly glycosylated, since the action of glycosylases on the enzyme obtained from these vesicles produced a similar stimulation to that with the melanosomal enzyme. Treatment of cultured melanocytes with tunicamycin elicited a decrease in the amount of active DCT inside the cells. All data suggest that the structure of the carbohydrate moiety of DCT should be very similar to, if not identical with, the structure proposed for tyrosinase by Ohkura, Yamashita, Mishima & Kobata (1984) Arch. Biochem. Biophys. 235, 63-77.