Studies on Tyrosinase in the Housefly

Part III. Activation of Protyrosinase by Natural Activator

Abstract

A natural activator occurring in the aged pupae of the housefly, Musca domestica Maquart, was partially purified by means of fractionation with ammonium sulfate and of lyophilization. The preparation of the activator without accompanying tyrosinase activity made it possible to devise a method for measuring its activity, i. e., a partially purified protyrosinase which contained no activator was incubated together with natural activator, and the formation of tyrosinase activity was followed either manometrically or colorimetrically. Effects of concentration of natural activator, pH and temperature on the activation of protyrosinase were studied, resulting in an assumption that the activation occurs catalytically. Inhibition of the activation by various chemical reagents were studies and it was found that sodium picryl sulfate, N-bromosuccinimide or iodine inactivated natural activator irreversibly, and thioglycol or monoiodoacetate inhibited considerably. However, these reagents have almost no effect on the potential activity of protyrosinase. As the results, it was presumed that natural activator is an enzyme and protyrosinase is its substrate. The mode of activation of protyrosinase by the activator is, however, still obscure.