The Membrane Domain of the Na-motive V-ATPase from Enterococcus hirae Contains a Heptameric Rotor*

In F-ATPases, ATP hydrolysis is coupled to transloca-tion of ions through membranes by rotation of a ring of c subunits in the membrane. The ring is attached to a central shaft that penetrates the catalytic domain, which has pseudo-3-fold symmetry. The ion transloca-tion pathway lies between the external circumference of the ring and another hydrophobic protein. The H or Na:ATP ratio depends upon the number of ring pro-tomers, each of which has an essential carboxylate in-volved directly in ion translocation. This number and the ratio differ according to the source, and 10, 11, and 14 protomers have been found in various enzymes, with corresponding calculated H or Na:ATP ratios of 3.3, 3.7, and 4.7. V-ATPases are related in structure and func-tion to F-ATPases. Oligomers of subunit K from the Na