Lipid environment of gastric potassium ion-stimulated adenosine triphosphatase

The K+-stimulated ATPase associated with the purified gastric microsomal fraction can be completely inactivated by treatment with 15% (v/v) ethanol for 60s at 37 degrees C, but not at 25 degrees C. Sequential exposure of the microsomal fraction to 15% ethanol at 25 degrees C and 37 degrees C caused release of 2.5% and 2.9% of the total membrane phospholipids respectively. Restoration of the enzyme activity was achieved by sonication with phosphatidylcholine in the presence of Mg2+, K+ and ATP, which were essential for the reconstitution. Our data suggest that the phospholipids extracted by 15% ethanol at 37 degrees C are derived primarily from the immediate lipid environment of the enzyme, and ATP, together with the metal ions, helps the partially delipidated enzyme to retain the appropriate configuration for the subsequent reconstitution.