Occurrence of Tyrosinase in Horse and Fish Melanomas

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Abstract
A crude extract with marked tyrosinase activity was prepared from melanomas of the horse and certain species of hybrid fish. These extracts catalyzed the oxidation of both tyrosine and dopa to melanin. In addition, dopa has a catalytic role in the enzymatic oxidation of tyrosine by these extracts. Diethyldithio-carbamate produces a marked inhibition of the enzymatic reaction. This inhibition is reversed by cupric ions in the case of the horse melanoma extracts. The reversal is not obtained with other metals. The enzymatic activity of horse melanoma extracts appears to be associated with cellular particulate matter, which is larger than that found in mouse melanoma extracts. The biochemical properties of the tyrosinase prepns. from the horse and fish melanomas are similar to the properties of the prepn. obtained from mouse melanoma.