ATPase Activity of the Sodium Pump needs Phosphatidylserine

Abstract

IT has frequently been suggested that the chemical properties of phospholipids and their prevalence in cell membranes make them particularly suitable compounds to serve as carrier molecules for the transport of cations. Some support for this suggestion has been provided by studies of the cation binding properties of phospholipids^1,2 and of various model systems involving phospholipids^3–5. Taken together, these investigations indicated that some phospholipids might be especially concerned in the active transport of Na⁺ and K⁺, but the evidence is not conclusive. The concept of such a carrier for ion transport antedates the work showing the involvement of ATP and its enzymatic hydrolysis in the Na⁺ pump; and during the past decade there has been a shift of interest and emphasis towards the role of the membrane ATPase system in active cation transport⁶. During this period, however, evidence has accumulated that the Na⁺, K⁺-activated ATPase is eliminated when lipids are removed from membranes by solvent extraction, treatment with detergents, or exposure to phospholipases^7–9. The question therefore arises whether phospholipid might provide a carrier system in which the protein of the ATPase is also involved, such that the ATPase activity depends on lipid as well as protein.