Interfacial polarization, transmembrane

Although the mechanisms of electroporation, electrofusion, and electroinsertion are not known, biophysical data suggest that the primary field pulse effect is interfacial polarization by ion accumulation at the membrane surfaces. The resulting transmembrane electric field causes rearrangements of the lipids such that pores are formed1718. Electropores anneal slowly (over a period of minutes) when the pulse is switched off. 

In this case, besides a molecular condenser due to the dipole array, 4770-1 = e"( A(0) - iA(/)), similar to that of the Stern layer, a diffuse layer potential due to electrolytes and the charges of dipoles may be formed in the aqueous solution which is slightly different from the double layer potential discussed above. Depending upon the magnitude of the dipoles /t and their orientation at the membrane surface, the contribution of such polarization potentials to the interfacial potential as well as to the transmembrane potential could be considerable. In addition, it is possible that molecular (nonspecific or specific) adsorption of ions or water molecules occurs. This would further complicate the profile of the diffuse layer potential. 

In general, it is expected that most peptides composed of mixtures of polar and nonpolar residues adopt amphiphilic, interfacially active structures. Whether these structures are ordered or not depends on the sequence of amino acids. In contrast, nonpolar peptides are expected to partition from water to a nonpolar medium. Since they are disordered in the aqueous solution but, most likely, exist as a-helices in a nonpolar environment, they must fold before they reach thermodynamic equilibrium in this environment, presumably during the transfer across the interface. This is clearly relevant to the insertion and formation of transmembrane helices and the translocation of proteins across the membrane initiated by signal sequences. 

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