Elucidation of mechanism for spontaneous molecular-recognition in lipid non-bilayer membranes

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In this study, we investigated the molecular recognition ability of lipid molecules in non-bilayer aggregates formed by phospholipids, that is, interdigitated gel and inverted hexagonal structures, by means of macroscopic methods such as differential scanning calorimetry and high-pressure light transmittance measurements and a microscopic method as a high-pressure fluorescent probe measurement. The obtained results are summarized as follows :1.The bilayer phase transitions for four kinds of N-methylated dipalmitoylphospatidylethanolamines with different-sized polar head groups under high pressure were examined. The stability and polymorphism of gel phases among the phospholipid bilayers were revealed.2.The barotropic phase transitions of asymmetric phosphatidylcholine bilayer membrane were observed. Interdigitation of asymmetric phosphatidylcholine was markedly different from those of symmetric ones.3.The fluorescence spectra of Prodan for the bilayer membranes of four kinds of diacylp … More hosphatidylcolines with varying acyl chain lengths were observed as a function of pressure. We speculated the location of the Prodan molecules in bilayer membranes in different phases from the shift of fluorescence spectra.4.The phase transition three kinds of phosphatidylcholine bilayer membranes in deuterium oxide and hydrogen oxide were examined. The substitution of hydrogen oxide by deuterium oxide produced a great effect on the transitions between gel phases and unstabilized the interdigitated gel phase.5.The fluorescence spectra of Prodan and Laurdan in bilayer membranes of phosphatidylcholine were observed as a function of pressure at constant temperature. In being formed the interdigitated gel phase, the Laurdan molecule was not squeezed out from the glycerol backbone region of phospholipid molecules because of the long acyl chain.6.The phase transition between the liquid crystal phase and the inverted hexagonal phase of dioleoylphosphatidylethanolamine bilayer membrane in aqueous NaCl solutions was investigated. We concluded that the transition can be regarded as the volume-driven transition for the reconstruction of molecular packing. Less