DOPACHROME TAUTOMERASE IS A ZINC-CONTAINING ENZYME

Dopachrome tautomerase (DCT) catalyzes the conversion of L-dopachrome into 5,6-dihydroxyindole-2-carboxylic acid through the melanogenic bio synthetic pathway. This enzyme, also named TRP2, belongs to the family of the tyrosinase related proteins. The three members of the family c ontain two highly conserved metal-binding sites with three histidines on each. Tyrosinase has copper at its active site. If was assumed that although DCT might have copper in those metal binding sites, its acti ve site could be related to other two putative iron-binding sites loca ted in different positions. Based on apoDCT preparation with cyanide a nd reconstitution experiments, we propose that DCT have zinc instead o f copper at the two metal-binding sites and that those sites actually correspond to the active site. The involvement of zinc, which cannot u ndergo redox reactions, accounts for the reaction that DCT catalyzes, a tautomerization versus the copper-mediated oxidations catalyzed by t yrosinase. (C) 1994 Academic Press, inc.