Enzymatic Digestion of Smooth Surfaced Membrane of Mouse Melanoma. I

Abstract

To study the state of tyrosinase [EC 1. 10. 3. 1] in the smooth sur-faced vesicles, the smooth surfaced membrane fraction isolated from Harding-Passey mouse melanoma was digested by Naja naja venom phospholipase A [EC 3. 1. 1. 4]. The digest was centrifuged and separated into two fractions: the supernatant and the precipitate. The amounts of protein and phospholipid and various enzyme activities including tyrosinase in each were determined. The effect of digestion on tyros-inase was different from its effects on other enzymes. The amount of tyrosinase activity solubilized was proportional to the amount of protein in the supernatant and the specific activities in the supernatant and sediment were almost the same. Furthermore, most of the tyrosinase activity remained in the residue of digested membranes. It is con-cluded from these results, that tyrosinase in the smooth surfaced vesicles is tightly bound to the protein moiety in the membranous structure as a constitutional element of the membrane.