.
The flagellum is linked to a flexible hook. The hook is attached to a series of protein rings (shown in red), which are embedded in the outer and inner (plasma) membranes. The rings form a rotor, which rotates with the flagellum at more than 100 revolutions per second. The rotation is driven by a flow of protons through an outer ring of proteins (see Figure 14-17), the stator, which also contains the proteins responsible for switching the direction of rotation. (Based on data from T. Kubori et al., J. Mol. Biol. 226:433–446, 1992, and N.R. Francis et al., Proc. Natl. Acad. Sci. USA 89:6304–6308, 1992.)