Synthesis In Vitro of 5,6-Dihydroxyindole-2-carboxylic Acid by Dopachrome Conversion Factor from Cloudman S91 Melanoma Cells

Abstract

The oxidation of dopachrome to melanin occurs spontaneously in vitro but has been shown to be under enzymatic control in vivo. Dopachrome conversion factor, purified from Cloudman S91 melanoma cells, converts dopachrome, which is orange, to a colorless compound. We have purified this colorless compound and identified it as 5,6-dihydroxyindole-2-carboxylic acid. This compound is generated enzymatically from a solution containing dopa and dopachrome and, under these conditions, is not readily oxidized to melanin in solution at pH 6.8. The synthesis in vitro of 5,6-dihydroxyindole-2-carboxylic acid suggests that this compound may be an intermediate in the synthesis of melanin.