sodium:potassium-exchanging ATPase complex sodium pump GO:0005890 cellular_component sodium/potassium-exchanging ATPase complex Sodium:potassium-exchanging ATPases are tetrameric proteins, consisting of two large alpha subunits and two smaller beta subunits. The alpha subunits bear the active site and penetrate the membrane, while the beta subunits carry oligosaccharide groups and face the cell exterior. cation-transporting ATPase complex plasma membrane protein complex