Deuterium magnetic resonance study of phase equilibria and membrane thickness in binary phospholipid mixed bilayers.
Deuterium magnetic resonance study of phase equilibria and membrane thickness in binary phospholipid mixed bilayers.
复制标题
二元磷脂混合双层中的相平衡和膜厚度的氘磁共振研究。
DOI：
10.1021/bi00150a020
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发表时间：
1992
期刊：
影响因子：
2.9
通讯作者：
Thompson,TE
中科院分区：
文献类型：
--
作者：
Sankaram,MB;Thompson,TE
摘要：采用固态宽谱2H NMR研究了由二豆脂酰磷脂酰胆碱（DMPC）和二硬脂酰磷脂酰胆碱（dsc）组成的双组分体系的凝胶-流体相平衡。通过光谱第一矩分析和差谱法定量凝胶相和流体相提供了温度-组成相图。构建过氘化DMPC、DMPC- DMPC- dspc >、DMPC- dspc -i/70混合物的相图。在这三种体系中，流体分数相差高达90%，而流体相的组成，即两种分子在流体相中的浓度之比，在整个温度和体系组成范围内相差约20%。在全流体或凝胶-流体共存区，DMPC-i/54和DSPC-i/70分子的有效酰基链长度随温度和组成的变化规律进行了计算。DMPC-i/54和DMPC-i/ 70分子在二元混合物的流体相中的热膨胀系数的大小都小于单独含有DMPC-i/ 70或DMPC-i/54的单组分双层中的热膨胀系数。此外，在流体相的任意温度下，DMPC-i/54的酰基链长随体系中DSPC含量的增加而增加的幅度小于DMPC混合物中DSPC-i/70的相应长度的增加。当二元混合物处于全流体或凝胶-流体共存区时，在整个温度和组成范围内，流体相中DMPC-i/54分子的最大值小于流体相中DSPC-i/70分子的最小值。用酰基链长度计算了液相双分子层的有效加权平均厚度d。厚度是根据时间和加权平均配置获得的，该配置允许光滑的双层表面，但在双层中心存在不匹配，导致部分交叉数字结构。正如预期的那样，在任何给定的dsc或DSPC-i/70摩尔分数下，温度升高都会导致d减小。无论体系是全流体还是处于凝胶-流体共存区，在任何给定温度下，流体相的双层厚度都随着dsc或DSPC-i/70摩尔分数的增加而近似线性增加。模型膜系统中基本物理和化学过程的生物学相关性导致了脂质组成对膜系统整体和局部结构特性影响的研究的重大努力（Cevc和Marsh， 1987）。在对不同模型系统的各种研究中，对磷脂混合物形成的双分子层的研究有望为对生物过程有直接影响的双分子层的结构和动力学提供见解。这是因为这些体系在化学成分上是不均匀的，表现出相分离，并形成孤立的平面内脂质结构域；在许多浆和细胞膜中发现的特征
Revised Manuscript Received June 17, 1992 abstract: The gel-fluid phase equilibrium in a two-component system formed from dimyristoylphosphatidylcholine (DMPC) and distearoylphosphatidylcholine (DSPC) was investigated using solid-state wide-line 2H NMR spectroscopy. Analysis of the spectral first moments and the quantitation of gel and fluid phases by means of difference spectroscopy provided the temperature-composition phase diagrams. Phase diagrams were constructed for mixtures of perdeuterated DMPC, DMPC- DMPC-DSPC> DMPC-DSPC-i/70. While the fluid fraction varies by as much as 90% among the three systems, the composition of the fluid phase, ie, the ratio of the concentrations of the two molecules in the fluid phase, variesby about 20% over the whole temperature and system composition range. The effective acyl chain lengths of the DMPC-i/54 and DSPC-i/70 molecules as a function of temperature and composition in the fluid phase, when the system is all fluid or is in the gel-fluid coexistence region, were calculated from the quadrupole splittings in the axially symmetric powder patterns obtained for the all-fluid phase. The magnitudes of the coefficient of thermal expansion for both the DMPC-i/54 and theDSPC-i/70 molecules were smaller in the fluid phase of binary mixtures than in one-component bilayers containing either DSPC-i/70 or DMPC-i/54 alone. In addition, at any given temperature in the fluid phase, the increase in the acyl chain length of DMPC-i/54 with increasing DSPC content of the system was smaller than the concomitant increase in the length of DSPC-i/70 in mixtures with DMPC. In the entire temperature and composition range when the binary mixtures are in the all-fluid or in the gel-fluid coexistence region, the largest value obtained for the DMPC-i/54 molecule in the fluid phase was smaller than the smallest value obtained for the DSPC-i/70 molecule in the fluid phase. The acyl chain lengths were used to calculate the effective weighted-average thickness, d, of the fluid phase bilayer. The thickness was obtained for a time-and weighted-average configuration, which allows for a smooth bilayer surface but has a mismatch at the center of the bilayerthat leads to a partially interdigitatedstructure. As expected, increasing the temperature at any given mole fraction of DSPC or DSPC-i/70 resulted in a decrease in d. Whether thesystem is all-fluid or is in the gel-fluid coexistence region, the bilayer thickness of the fluid phase at any given temperature was found to increase nearly linearly with increasing mole fraction of DSPC or DSPC-i/70 in the fluid phase.The biological relevance of fundamental physical and chemical processes in model membrane systems has led to a major effort in studies of the influence of lipid composition on the global and local structural properties of membrane systems (Cevc & Marsh, 1987). Among the various studies on different model systems, investigations on bilayers formed from mixtures of phospholipids are expected to provide insights into the structure and dynamics of bilayers that have a direct impact on biological processes. This is because these systems are heterogeneous in chemical composition, exhibit phase separation, and form isolated in-plane lipid domains; features which are found in many plasma and intracellular membranes