2 B ENZYMATIC CYCLE OF THE Na-K PUMP Three Na ions within the cell then bind to sites on Et The E, form of the pump, binding with ATP bound, is empty sites and exposed to intra- 3 An AtP molecule binds The ATP molecule is hydrolyze Excusing a conform- phosphorylating the a subunit. ational change to the This phosphorylation of E, results pump, which returns it to in a conformational change, which its E, state K is exposed occludes Na from both the to the cytosolic space and cytosolic and extracellular space. The conformation of the 7 pump spontaneously changes Phosphate leaves E2 which hanges its conformation Nat to the extracellular space once again and occludes K allowing it to exit the pump. Ouabain inding Ouabain binds to ErP, changing the conform- ation of the pump and blocking the pore. The pump is nonfunctionaL. 鑫 6 TwoKions outside I the cell bind to sites K The ErP form of pump is mpty and exposed to the extracellular space