| Abstract: | ![]()
A tyrosinase has been purified from the skin of the frog Xenopus laevis. Dihydroxyphenylalanine oxidase and tyrosine hydroxylase activities co-purify throughout the procedure. The enzyme is isolated in an inactive form, but both enzymatic activities are activated by a variety of anionic detergents. Of these, sodium dodecyl sulfate (NaDodSO4) is the most effective. The enzyme activation occurs at NaDodSO4 concentrations well below the critical micelle concentration and it remains active at concentrations as high as 30 mM (1%). Neither activity is stimulated by cationic or nonionic detergents, or a variety of other agents, including trypsin. The purified tyrosinase is a glycoprotein having a polypeptide Mr = 175,000 by NaDodSO4-polyacrylamide gel electrophoresis. This monomeric species is enzymatically active in the presence of NaDodSO4. Detergent-activated tyrosinase has a KM for dihydroxyphenylalanine of 6 X 10(-4) M and a KM for tyrosine of 4 X 10(-4) M. Both activities are inhibited by copper chelators but not by an iron chelator. Further characterization of the detergent activation of this enzyme is presented in a companion paper (Wittenberg, C., and Triplett, E. L. (1985) J. Biol. Chem. 260, 12542-12546). |
