Purification and Properties of the F(1)F(o) ATPase of Ilyobacter tartaricus, a Sodium Ion Pump

The ATPase of Ilyobacter tartaricus was solubilized from the bacterial membranes and purified. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme revealed the usual subunit pattern of a bacterial F(1)F(o) ATPase. The polypeptides with apparent molecular masses of 56, 52, 35, 16.5, and 6.5 kDa were identified as the α, β, γ, ɛ, and c subunits, respectively, by N-terminal protein sequencing and comparison with the sequences of the corresponding subunits from the Na(+)-translocating ATPase of Propionigenium modestum. Two overlapping sequences were obtained for the polypeptides moving with an apparent molecular mass of 22 kDa (tentatively assigned as b and δ subunits). No sequence could be determined for the putative a subunit (apparent molecular mass, 25 kDa). The c subunits formed a strong aggregate with the apparent molecular mass of 50 kDa which required treatment with trichloroacetic acid for dissociation. The ATPase was inhibited by dicyclohexyl carbodiimide, and Na(+) ions protected the enzyme from this inhibition. The ATPase was specifically activated by Na(+) or Li(+) ions, markedly at high pH. After reconstitution into proteoliposomes, the enzyme catalyzed the ATP-dependent transport of Na(+), Li(+), or H(+). Proton transport was specifically inhibited by Na(+) or Li(+) ions, indicating a competition between these alkali ions and protons for binding and translocation across the membrane. These experiments characterize the I. tartaricus ATPase as a new member of the family of FS-ATPases, which use Na(+) as the physiological coupling ion for ATP synthesis.