Diffusion-Influenced Transport of Ions across a Transmembrane Channel with an Internal Binding Site.

We develop a microscopic theory for ion transport across a transmembrane channel with an internal binding site. The ion flux is determined by the rate constants for binding to the internal site from the two sides of the membrane and the corresponding unbinding rate constants. The binding rate constants are formulated in terms of diffusion-influenced reactions. The theory allows a reconciliation of experimental data on the conductance of the influenza A M2 proton channel with the structure and dynamics of the protein.