Polar Interactions Play an Important Role in the Energetics of the Main Phase Transition of Phosphatidylcholine Membranes.

Conformational changes of membrane proteins are accompanied by deformation in the surrounding lipid bilayer. To gain insight into the energetics of membrane deformation, the phase behavior of dimyristoylphosphatidylcholine (DMPC) membranes in the presence of the dipole potential, ψ, modifiers was investigated by differential scanning calorimetry. 7-Ketocholesterol, which weakens ψ and reduces membrane-perpendicular dipole-dipole repulsion, causes a discrete second peak on the high-temperature side of the main transition, whereas 6-ketocholestanol, which strengthens ψ and increases membrane-perpendicular dipole-dipole repulsion, merely produces a shoulder.