Channel-facilitated membrane transport: Constructive role of particle attraction to the channel pore

We approach channel-facilitated membrane transport using a stochastic model based on considerations of particle diffusion inside the channel pore. This model allows us to rationalize the experimental observation that metabolite-specific biological channels exhibit affinities to their metabolites. We demonstrate that there is an optimal attractive interaction between the channel and the particle that maximizes the particle flux through the channel. A model in which the translocating solute jumps between neighboring binding sites is also analyzed. It is shown that the results predicted by the diffusion model can be recovered from the analysis of the binding-site model in a special limiting case. The binding-site model also describes the flux through a narrow channel where molecules cannot jump one over the other, and the regime of single-file diffusion is realized.