... looselyarranged, and the densities correspond to the N- and C-terminal helices of the c ring, respectively. The C-terminal helices show a clear handedness, and two of the rings face in the opposite ... represent the view from the cytoplasm (open rings in AFM) and the red ones the view from the extracellular side (smaller, closedrings in Fig. 3). The inner and outer diameters of the rings, measured ... of the ion-binding site. Therefore, the c ring of A. woodii hasonly 10 membrane-buried negative charges that areessential for binding the ion and also for the rotationalmechanism of the ring....