Abstract
DOPA quinone imine conversion factor was partially purified from larval hemolymph of the silkworm, Bombyx mori, using a novel assay. The factor was labile at 4°C below pH 5 and above pH 11, and at pH 8.5 above 55°C. Activity of the factor was maximal at pH 7.5-9. The factor catalyzed the decolorizations of L-DOPA methyl ester and α-methyl DOPA methyl ester chromes besides DOPA quinone imine. HPLC analysis indicated that the factor-catalyzed decolorization reaction of DOPA quinone imine resulted in the accumulation of dihydroxyindole. Based on spectral changes of α-methyl DOPA methyl ester chrome, it was suggested that the factor catalyzed the intramolecular oxidoreduction of DOPA quinone imine. During the oxidation of L-DOPA with endogenous phenoloxidase, the factor facilitated the formation of melanochrome.
