Barotropic and Thermotropic Phase Behavior of Bilayer Membranes Composed of Phospholipids Containing Cis Double Bond in the sn-2 Acyl Chain
The phase transitions of two kinds of saturated (in the sn-1 position) and unsaturated (in the sn-2 position) mixed-chain phospholipids, 1- palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1- palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), were observed by high-pressure optical method and differential scanning calorimetry. The temperature-pressure phase diagrams were constructed on the basis of the obtained phase-transition data and the results were compared with those of saturated-chain phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and those of unsaturated-chain phospholipids, 1,2-dioleoyl-snglycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-sn-glycero-3- phosphocholine (DOPC). The phase transition temperatures of mixed-chain lipids showed the intermediate values for the bilayer membranes between saturated-and unsaturated-chain lipids. The thermodynamic quantities of the transition for mixed- and unsaturated-chain lipid bilayer membranes were smaller than those for saturated-chain lipids. The transition temperatures of POPE and POPC bilayer membranes were significantly different although the thermodynamic quantities of the transition for both bilayers resembled each other in magnitude.
KeywordsEntropy Enthalpy Calorimetry Choline Phosphatidylcholine
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