On the limits of facilitated diffusion

Abstract Facilitated diffusion normally involves mobile carriers, reactive groups which react with specific solutes and diffuse with them across a liquid membrane. Facilitated diffusion can also occur via carriers which are covalently bound to a solid membrane if the carriers still have some limited mobility. The solute flux across such chained carrier membranes varies with solute concentration just like the flux across mobile carrier membranes. The solute flux across chained carrier membranes shows different behavior vs. carrier concentration, including a percolation threshold.