title: Chymotrypsin activation of melanosome tyrosinase in hamster melanotic melanoma.
abstract: The tyrosinase activity in two sucrose gradient isolated melanosome fractions from a melanotic hamster melanoma was found to increase after alpha-chymotrypsin treatment. The enhancement in tyrosinase activity had its maximum at a concentration of 1 mg/ml alpha-chymotrypsin after 120 min incubation at 37 degrees C. No direct activating effect of alpha-chymotrypsin was found either on the soluble tyrosinase fraction from freshly prepared untreaed whole-tumor homogenate or on purified mushroom tyrosinase. The activating effect of alpha-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 alpha-chymotrypsin treatment of melanosomes might indicate the existence of an "enzyme liberating" mechanism in the melanosomes.
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000378:metabolism*; D002918:Chymotrypsin / Q000494:pharmacology*; D006224:Cricetinae; D004789:Enzyme Activation / Q000187:drug effects; D008543:Melanins / Q000096:biosynthesis; D008544:Melanocytes / Q000187:drug effects* / Q000378:metabolism; D008545:Melanoma / Q000188:drug therapy / Q000378:metabolism*; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D009374:Neoplasms, Experimental / Q000378:metabolism; D013997:Time Factors
chemical_list: D008543:Melanins; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; D002918:Chymotrypsin