Purification and properties of a cytosol Ca2+-activated ATPase from Tetrahymena pyriformis

A Ca2+-activated ATPase has been isolated from the cytosol of Tetrahymena pyriformis. The enzyme, whose specific activity increases with culture age, was purified to homogeneity from extracts of stationary phase cells. The pure enzyme which has a molecular weight of 89,000 was found to contain three identical subunits of molecular weight approximately 29,000. ATP is the preferred substrate for the enzyme and maximal activity is dependent on either Ca2+ or Ba2+. Inhibitors of known ATPases do not affect the enzyme activity. Antibodies developed against the pure enzyme only react with ATPase in the cytosol fraction prepared by differential centrifugation of a crude homogenate of cells. The function of the cytosol ATPase which has, thus far, only been detected in various strains of Tetrahymena pyriformis is presently under investigation.