López-García F, Villalaín J, Gómez-Fernández J C, Quinn P J
Departmento de Bioquímica y Biología Molecular (A), Universidad de Murcia, Spain.
Biophys J. 1994 Jun;66(6):1991-2004. doi: 10.1016/S0006-3495(94)80992-0.
The phases and transition sequences for aqueous dispersions of mixtures of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycerol (1,2-DPG) have been studied by differential scanning calorimetry, dynamic x-ray diffraction, freeze-fracture electron microscopy, 31P-nuclear magnetic resonance spectroscopy, and Fourier-transform infrared spectroscopy. The results have been used to construct a dynamic phase diagram of the binary mixture as a function of temperature over the range 20 degrees-90 degrees C. It is concluded that DPPC and 1,2-DPG form two complexes in the gel phase, the first one with a DPPC/1,2-DPG molar ratio of 55:45 and the second one at a molar ratio of approximately 1:2, defining three different regions in the phase diagram. Two eutectic points are postulated to occur: one at a very low 1,2-DPG concentration and the other at a 1,2-DPG concentration slightly higher than 66 mol%. At temperatures higher than the transition temperature, lamellar phases were predominant at low 1,2-DPG concentrations, but nonlamellar phases were found to be predominant at high proportions of 1,2-DPG. A very important aspect of these DPPC/1,2-DPG mixtures was that, in the gel phase, they showed a ripple structure, as seen by freeze-fracture electron microscopy and consistent with the high lamellar repeat spacings seen by x-ray diffraction. Ripple phase characteristics were also found in the fluid lamellar phases occurring at concentrations up to 35.6 mol% of 1,2-DPG. Evidence was obtained by Fourier transform infrared spectroscopy of the dehydration of the lipid-water interface induced by the presence of 1,2-DPG. The biological significance of the presence of diacylglycerol in membrane lipid domains is discussed.
通过差示扫描量热法、动态X射线衍射、冷冻蚀刻电子显微镜、³¹P核磁共振光谱和傅里叶变换红外光谱，研究了1,2 - 二棕榈酰 - sn - 甘油 - 3 - 磷酸胆碱（DPPC）和1,2 - 二棕榈酰 - sn - 甘油（1,2 - DPG）混合物的水分散体的相和转变序列。这些结果被用于构建二元混合物在20℃至90℃温度范围内随温度变化的动态相图。得出的结论是，DPPC和1,2 - DPG在凝胶相中形成两种复合物，第一种复合物的DPPC/1,2 - DPG摩尔比为55:45，第二种复合物的摩尔比约为1:2，这在相图中定义了三个不同的区域。推测存在两个共晶点：一个在1,2 - DPG浓度非常低时，另一个在1,2 - DPG浓度略高于66 mol%时。在高于转变温度时，在低1,2 - DPG浓度下，层状相占主导，但在高比例的1,2 - DPG下，非层状相占主导。这些DPPC/1,2 - DPG混合物的一个非常重要的方面是，在凝胶相中，它们呈现出波纹结构，这通过冷冻蚀刻电子显微镜观察到，并且与X射线衍射观察到的高层状重复间距一致。在1,2 - DPG浓度高达35.6 mol%时出现的流体层状相中也发现了波纹相特征。通过傅里叶变换红外光谱获得了证据，证明1,2 - DPG的存在会引起脂质 - 水界面的脱水。讨论了膜脂区域中二酰基甘油存在的生物学意义。
