The ability of ATP, CTP, ITP, GTP, UTP and two synthetic ATP analogs to provide for ouabain-sensitive Na+ accumulation into proteoliposomes with a reconstituted Na+,K+-ATPase (ATP phosphohydrolase, EC 3.6.1.37) was investigated. A correlation between the proton-accepting properties of the nucleotides and their ability to provide for active transport was found. The proton-accepting properties of the substrate seem to be a necessary condition for the shift from the K-form to Na form of Na+,K+- ATPase — an immutable step in the active translocation of Na+ and K+ through the Na+ pump.
