title: Half-lives of tyrosinase isozymes from Harding-Passey mouse melanoma.
abstract: The half-lives of tyrosinase isozymes, a key enzyme in melanogenesis, have been determined using two different approaches: (a) cycloheximide treatment of mice bearing growing tumors and measurement of the residual enzymatic activity. This approach detected two soluble forms of cytosolic tyrosinase with half-lives of 1/2 and 8 h, respectively. The melanosomal isozyme showed a t1/2 of 3 1/2 h. (b) Metabolic labelling of tyrosinase with [35S]Met and immunoprecipitation analysis using a monoclonal antityrosinase. This method gave values slightly longer, 5 h and 9 1/2 h for the melanosomal and cytosolic tyrosinase, respectively. The origin of soluble tyrosinase and its utility to employ that enzymatic activity in melanoma chemotherapy using catechols as tyrosinase-dependent precursors of cytotoxic quinones is discussed.
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000032:analysis*; D003513:Cycloheximide / Q000494:pharmacology; D006207:Half-Life; D007527:Isoenzymes / Q000032:analysis*; D008546:Melanoma, Experimental / Q000201:enzymology*; D051379:Mice; D008810:Mice, Inbred C57BL; D014442:Monophenol Monooxygenase / Q000032:analysis*
chemical_list: D007527:Isoenzymes; D003513:Cycloheximide; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase