Induction of lateral phase separations in binary lipid mixtures by alcohol

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Abstract
It has previously been shown that alcohol has different effects on the gel to liquid-crystal phase transition of phosphatidylcholines (PC''s) and phosphatidylethanolamines (PE''s) [Rowe, E. S. (1985) Biochim. Biophys. Acta 813, 321-330]. In this investigation, the thermotropic properties of binary PE-PC mixtures were studied in the presence of ethanol in order to determine whether the differential interactions of alcohol with PC and PE would lead to lateral phase separations. Phase diagrams of the dilaurylphosphatidylethanolamine-dipalmitoylphosphatidylcholine [PE(12:0)-PC(16:0)] system were constructed in the presence and absence of ethanol. It was shown that lateral phase separations occur in the gel phase over a certain composition range in the presence of 100 mg/mL ethanol. In the absence of alcohol these two lipids are miscible in both the gel and liquid-crystal states. The data suggest that in the presence of ethanol these lateral phase separations involve the coexistence of regular bilayer gel and the fully interdigitated gel phase, which has previously been shown to occur in pure PC(16:0) under these conditions [Simon, S. A., and McIntosh, T. J. (1984) Biochim. Biophys. Acta 773, 169-172]. The biological implications of these findings are discussed.