Mutual Exclusion of ATP,ADP and g-Strophanthin Binding to NaK-ATPase

THE (Na⁺+K⁺)-activated ATPase found in cell membrane fragments is for many reasons thought to be part of the active sodium pump system of cells. One of the arguments is that cardiac glycosides specifically inhibit the ATPase as well as the sodium pump^1–3. It has been proposed that the inhibition is due to an interaction between the glycosides and some phosphorylated form of the ATPase system^4–6.