Preparation and Properties of Purified (Na+ + K+)-Stimulated Mitochondrial ATPase from Germinating Pea Seeds

Abstract

An ATPase preparation from pea cotyledon mitochondria was purified by protamine sulfate, ammonium sulfate precipitations, and preparative gel electrophoresis. The ATPase activity was dependent upon Mg²⁺ and stimulated by Na⁺ + K⁺. The optimum pH of the enzyme was 8.0. A ratio of 5 to 1 between Na⁺ and K⁺ must be maintained to show maximum ATPase activity. Although no detectable amounts of phospholipids were found to be associated with the purified enzyme, it was activated by Na⁺ and K⁺ ions. Addition of phosphatidylserme and phosphatidylinositol resulted in increased activity of the (Na⁺ + K⁺)-stimulated enzyme, suggesting that the purified enzyme has probably lost most of the membrane complement during purification.