The effect of the dielectric constant of proteins on the ionic transport processes in biomembranes

Abstract

It has been shown that high efficiency of the ionic transport processes in biomembranes modified by protein ionic channels or carriers of peptide structure is determined by a high polarizability of these molecular systems, which is expressed by their large dielectric constant ϵ. According to our estimates, the minimal value of ϵ for proteins is equal to 20, i.e. it is closer to ϵ water, = 80 than to ϵ lipid = 2. In this connection we have considered in detail the effect of the dielectric constant of protein ion-transporting systems on the potential-dependent characteristics of ionic transport processes, on the processes of complex formation between permeant ions and anionic groups of the ionic channel, and cationic repulsion in the channel. In the framework of the concept developed the enthalpy of solvation of alkaline metal cations in water and proteins were calculated. The difference between these values is equal to 8–10 kcal/Mole, which is quite close to the value of the enthalpy of activation for ionic transport processes in biomembranes. This fact shows that only proteins (due to their high polarizability) appear to provide a high performance of the ionic transport systems in biomembranes.