Some properties of the active site and cation binding site of the heart sarcolemmal (Na+ + K+)-ATPase.

It was demonstrated the presence of an essential sulfhydryl group recognizing and binding ATP in the active site of the heart sarcolemmal (Na+ + K+)-ATPase. Modulation of the degree of dissociation of the essential sulfhydryl group has a regulatory influence on affinity of the enzyme to ATP. The hydroxylic group in position two on the ribose moiety of ATP molecule proved to be of minor significance for binding of ATP to the active site of (Na+ + K+)-ATPase but participates considerably in reaction steps following the recognition and binding of ATP. It was identified the presence of an essential amino group in the potassium binding site of the (Na+ + K+)-ATPase molecule.