Binding of Ouabain to Na⁺, K⁺-Dependent ATPase during the ATPase Reaction

Evidence for a Dimer Structure of the ATPase

抄録

Na⁺, K⁺-dependent ATPase [EC 3.6.1.3] was purified from porcine kidney by the method of Lane et al. [(1973) J. Biol. Chem. 248, 7197-7200] with slight modifications [Yamaguchi, M. & Tonomura, Y., (1979) J. Biochem. 86, 509-523].
The amounts of a phosphorylated intermediate (EP) and ouabain bound to the enzyme during the ATPase reaction were measured in 2.1mM MgCl₂ and various concentrations of NaCl and KC1 at pH 7.5 and 20°C. In the presence of NaCl and the absence of KCI, the molar ratio of the amounts of EP and bound ouabain was 1 : 2. In the presence of both NaCl and KCl, it was 1 : 1. In both cases, the amount of bound ouabain was equal to that of EP in the absence of ouabain.
These findings suggest that the functional unit of the transport ATPase is a dimer.