Figure 5. (A) Diagrammatic representation of solvation energies estimated from relative permeability ((ΔGsolv)p) and relative block ((ΔGsolv)b) plotted vs.

Figure 5

(A) Diagrammatic representation of solvation energies estimated from relative permeability ((ΔGsolv)p) and relative block ((ΔGsolv)b) plotted vs. 1/r. The total solvation energy seen at the anion binding site (ΔGsolv)b is depicted as comprising an intercept (“inner-sphere” energy) and a “background” component that varies with 1/r. The change in background solvation with 1/r at the binding site is imagined as being somewhat less than that encountered in accessing the binding site because it pertains only to “background solvation” due to polarizable moieties beyond the inner-sphere. The apparent dielectric constant is expected to be less than that portrayed in the “effective” dielectric constant computed for the variation in permeability ratios, as this takes into account the entire stablization energy. This diagram illustrates the importance of the difference in ΔGhyd and ΔGsolv in determining permeability and binding selectivity. (B) A model for the channel featuring a central “narrow region” that is rate limiting for anion flow, flanked by two wider vestibules. The energy diagram is drawn to suggest the possibility that the barriers to anion flow could represent anion entry from the vestibule into the narrow region of the channel, whereas the transfer free energy from bulk water into the vestibule is roughly zero due to the abundance of water in this space.

From: Anion Conduction by CFTR: Mechanisms and Models

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