Figure 11.

A model for a leash-based F_o ratchet mechanism during F_oF₁-ATP synthesis. (A) The end of the leash prevents further counterclockwise rotation. Excess H⁺ (green dots) on the periplasmic side indicates a PMF. (B) The leash limits Brownian-dependent back and forth c-ring motion to 36°. During clockwise rotation, subunit-a aR210 (blue square) displaces the H⁺ (black dot) from yellow subunit-c cD61 (red dot) to the cytoplasmic half-channel (C), whereas the adjacent white subunit-c cD61 becomes protonated (light green dot) from the periplasmic half-channel (P). (C) The interaction responsible for the transient dwell dissociates. (D) Formation of the interaction at the end of the leash with the adjacent subunit-c ratchets the c-ring clockwise with H⁺ translocation to power ATP synthesis.