Abstract
Summary
1. A crude extract with marked tyrosinase activity has been prepared from melanomas of the horse and certain species of hybrid fish. These extracts catalyzed the oxidation of both tyrosine and dihydroxyphenyl-L-alanine (dopa) to melanin. In addition. dopa has a catalytic role in the enzymatic oxidation of tyrosine by these extracts.
2. Diethyldithiocarbamate, a substance with strong affinity for copper, produces a marked inhibition of the enzymatic reaction. This inhibition is reversed by cupric ions in the case of the horse melanoma extracts. This reversal is not obtained with other metals.
3. 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.
4. The biochemical properties of the tyrosinase preparations from the horse and fish melanomas are similar to the properties of the preparation obtained from mouse melanoma.
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