Chymotrypsin activation of melanosome tyrosinase in hamster melanotic melanoma

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Abstract
The tyrosinase activity in two sucrose gradient isolated melanosome fractions from a melanotic hamster melanoma was found to increase after α-chymotrypsin treatment. The enhancement in tyrosinase activity had its maximum at a concentration of 1 mg/ml α-chymotrypsin after 120 min incubation at 37°C. No direct activating effect of α-chymotrypsin was found either on the soluble tyrosinase fraction from freshly prepared untreated whole-tumor homogenate or on purified mushroom tyrosinase. The activating effect of α-chymotrypsin upon the melanosome tyrosinase is believed to be due to the endopeptidic hydrolysis of the-CO−NH-bound existing between tyrosinase and tyrosine and phenylalanine residues in the melanin molecule. Although alternative interpretations are not excluded, the observed enhancement in tyrosinase activity after α-chymotrypsin treatment of melanosomes might indicate the existence of an “enzyme liberating” mechanism in the melanosomes.