THE EXTRACTION AND ASSAY OF THE TYROSINASE FROM FROG SKIN: A STUDY ON THE INFLUENCE OF THE MELANOPHORE-STIMULATING HORMONE ON THE SYNTHESIS OF THE ENZYME

Abstract

A soluble (microsomal) preparation of tyrosinase was obtained from frog skin (Rana pipiens) by pretreatment of strips of dorsal skin with trypsin. The relatively high activity of the enzyme towards tyrosine compared with that against dopa and other catechols would indicate that the enzyme is predominantly of the nature of a monophenolase. The rate of oxidation of D-tyrosine is about one-third that obtained with L-tyrosine. The activity of the enzyme (measured by oxygen consumption of the system) with dialyzed preparations could be increased up to fivefold by the addition of cupric ions. The enzyme is inhibited in the presence of copper-binding agents such as diethyldithiocarbamate. Highly purified specimens of intermedin had no effect on the production or turnover of tyrosinase in the frog skin, nor was there any effect on the tyrosinoxidase. There was little difference in the activity of the tyrosinase in light- or dark-adapted frogs, or in frogs which had received a series of injections of intermedin. The tyrosinase activity of the skin is subject to a large seasonal variation. The activity is about ten times greater during the period September to November than in the earlier period of the year.