Fig. 5.

Structural model for channel activation by pH. Vertical arrows indicate equilibration between small- and large-kink conformations; the lengths of these arrows indicate the magnitudes of tendencies. Horizontal arrows indicate proton release or uptake. The curly brackets signify that the small- and large-kink conformations are in fast exchange on the time scales of proton release and uptake. Note that in the protonated state it is the minority population of large-kink conformations that is most likely to release the proton.