Gramicidin single-channel properties show no solvent-history dependence

The structure of membrane-associated gramicidins can depend on the solvent in which they were dissolved prior to membrane incorporation (LoGrasso, P. V., F. Moll, and T. A. Cross 1988. Biophys. J. 54:259-267; Killian, J. A., K. U. Prasad, D. Hains, and D. W. Urry. 1988. Biochemistry. 27:4848-4855). The peptide's solvent history might thus affect the functional characteristics of gramicidin channels (op. cit.). We tested this proposal by examining the properties (conductance, conductance dispersity, and average duration) of channels formed by [Val1]gramicidin A that had been dissolved in eight different solvents. The peptide was incorporated into lipid bilayers either by addition to the aqueous phase (and subsequent adsorption to the membrane) or by cosolubilization with the membrane-forming phospholipid. When the peptide was cosolubilized with the phospholipid, the channel properties did not vary with the solvent used. When the peptide was dissolved in chloroform, benzene, or trifluoroethanol and added through the aqueous phase, the channel properties differed from those found when gramidicin was dissolved in methanol, ethanol, dioxane, dimethylsulfoxide, or ethylacetate. The changes observed with the former three solvents were reproduced by adding them to the aqueous phase, and are therefore due to the ability of these solvents to partition into the membrane and alter the channels' behavior.