Reactivation of a phospholipid-depleted sodium, potassium-stimulated ATPase

1. 1. The effect of phospholipids on (Na+-K+)-ATPase was studied in a particulate preparation from bovine heart. 2. 2. After treatment with ultrasonic oscillations the complex became partially soluble in a solution of nonionic detergent lubrol. Fractionation of "solubilized" ATPase with (NH4)2SO4, followed by washing in NaCl solutions, resulted in a preparation depleted of phospholipids as well as cholesterol and largely devoid of ATPase activity. 3. 3. Total phospholipids from various sources as well as individual purified phospholipids restored the ATPase activity which was 90% inhibited by ouabain. Reconstruction was accompanied by reuptake of lost phospholipids. Differences among phospholipids were recorded: phosphatidylserine and disphosphatidylglycerol were the most effective but active preparations were also obtained with phosphatidylcholine and phosphatidylethanolamine. Cholesterol added as aqueous emulsion was ineffective. 4. 4. It is concluded that activation of (Na+-K+)-ATPase by phospholipids is a rather aspecific process. Although phosphatidylserine shows remarkable affinity for the enzyme complex and presumably plays an important role in maintaining the activity of the ATPase, it can not be considered as a specific activator. In agreement with recent observations on particulate mitochondrial ATPase from rat liver, acidic phospholipids showed greater effectiveness in the reactivation of transport ATPase and could be bound better. © 1972.