Mg-dependent ecto-ATPase of the erythrocyte plasma membrane of the scorpion fish Scorpaena porcus:: Biochemical properties and kinetic characteristics

A high surface ATPase activity was found in intact erythrocytes of Scorpaena porcus. The influx of tritium-labeled ATP ([H-3]-ATP) into the erythrocytes of this fish species was three orders of magnitude higher than the revealed activity of the enzyme. Thus, the ATPase appears to be located at the external erythrocyte surface of S. porcus. The enzyme has a wide substrate specificity to macroergic nucleotides and hydrolyses ATP at the maximum rate. The kinetic constants (K-M, V-max) were determined at the temperatures of 5, 15, and 25 degreesC. The maximum activity of the enzyme was observed at 25 degreesC, at pH 7.2-7.4, and in the presence of 3-6 mM Mg2+.