DOPACHROME TAUTOMERASE DECREASES THE BINDING OF INDOLIC MELANOGENESISINTERMEDIATES TO PROTEINS

Dopachrome tautomerase (DCT) is a recently characterized enzyme contri buting to the control of melanogenesis in mammals. The enzyme catalyze s the rearrangement of L-Dopachrome (L-DC) to 5,6-dihydroxyindole 2-ca rboxylic acid (DHICA), while the spontaneous rearrangement of L-DC lea ds to 5,6-dihydroxyindole (DHI). Due to the lower reactivity of DHICA in comparison to DHI, DCT could provide a protective mechanism against the cytotoxicity of decarboxylated indolic melanogenic intermediates by limiting the formation of these highly reactive decarboxylated spec ies within melanocytes. We have followed the binding of radioactive me lanogenic precursors to a model protein, bovine serum albumin (BSA). U sing L-DC as initial melanin precursor, this binding was decreased by DCT in a concentration-dependent manner. In the presence of tyrosinase , the binding of L-Dopa-derived intermediates to BSA was also decrease d by DCT and the percentage of decrease was even higher than using L-D C as initial melanin precursor. SDS-PAGE followed by fluorographic det ection of radioactive bands showed the formation of covalent adducts b etween BSA and melanin precursors, as well as of aggregated forms of t his protein. This aggregation was also diminished by DCT. These data i ndicate that DCT could play a protective role against the cytotoxic ac tion of decarboxylated indoles within mammalian melanocytes.