The cardiac glycoside receptor: its properties and its correlation to nucleotide binding sites, phosphointermediate,...

Binding of ouabain to its receptor is followed by a directly proportional inhibition of (Na++K+)-ATPase. The stoichiometry of nucleotide binding site, phosphate acceptor site, ouabain binding site in (Na++K+)-ATPase is 1:1:1. Inactivation of (Na++K+)-ATPase by S-[2,4-Dinitrophenyl]-6-mercaptopurine riboside-5'-triphosphate, which probably forms a thioether derivative of ATP with the enzyme, results in the appearance of a low affinity binding site. It is concluded that the covalently bound ATP fixes the enzyme in a E1 conformational state which is characterized by a low affinity for ouabain.