Interactions of a Photo-Affinity ATP Analog with Cation-Stimulated Adenosine Triphosphatases of Human Red Cell Membranes

To identify and isolate ATP binding and hydrolyzing sites of human red cell membranes we have synthesized a photo-activated ATP analog, 8-azido adenosine triphosphate (N₃ATP). In the absence of ultraviolet light it is a substrate for both the Mg-ATPase and the ouabain-sensitive, Na,K-ATPase. Hydrolysis of N₃ATP is prevented by increasing concentrations of ATP. Photolysis of N₃ATP with red cell membranes results in covalent incorporation and irreversible inhibition of both ATPase activities. Also, only three protein components of the red cell membranes are labeled. This labeling is completely abolished by appropriate concentrations of ATP.