Pott T, Maillet J C, Dufourc E J
Centre de Recherche Paul Pascal, Centre National de la Recherche Scientifique, Pessac, France.
Biophys J. 1995 Nov;69(5):1897-908. doi: 10.1016/S0006-3495(95)80060-3.
The effect of pH and cholesterol on the dimyristoylphosphatidic acid (DMPA) model membrane system has been investigated by solid state 2H- and 31P-NMR. It has been shown that each of the three protonation states of the DMPA molecule corresponds to a 31P-NMR powder pattern with characteristic delta sigma values; this implies additionally that the proton exchange on the membrane surface is slow on the NMR time scale (millisecond range). Under these conditions, the 2H-labeled lipid chains sense only one magnetic environment, indicating that the three spectra detected by 31P-NMR are related to charge-dependent local dynamics or orientations of the phosphate headgroup or both. Chain ordering in the fluid phase is also found to depend weakly on the charge at the interface. In addition, it has also been found that the first pK of the DMPA membrane is modified by changes in the lipid lateral packing (gel or fluid phases or in the presence of cholesterol) in contrast to the second pK. The incorporation of 30 mol% cholesterol affects the phosphatidic acid bilayer in a way similar to what has been reported for phosphatidylcholine/cholesterol membranes, but to an extent comparable to 10-20 mol % sterol in phosphatidylcholines. However, the orientation and molecular order parameter of cholesterol in DMPA are similar to those found in dimyristoylphosphatidylcholine.
通过固态2H和31P核磁共振研究了pH值和胆固醇对二肉豆蔻酰磷脂酸（DMPA）模型膜系统的影响。结果表明，DMPA分子的三种质子化状态中的每一种都对应于具有特征性δσ值的31P核磁共振粉末图谱；这还意味着膜表面的质子交换在核磁共振时间尺度（毫秒范围）上是缓慢的。在这些条件下，2H标记的脂质链仅感知一种磁性环境，这表明31P核磁共振检测到的三种光谱与磷酸头部基团的电荷依赖性局部动力学或取向或两者有关。还发现流体相中的链有序性也弱依赖于界面处的电荷。此外，还发现与第二个pK不同，DMPA膜的第一个pK会因脂质侧向堆积（凝胶或流体相或存在胆固醇）的变化而改变。掺入30 mol%的胆固醇对磷脂酸双层的影响方式与磷脂酰胆碱/胆固醇膜的报道类似，但程度与磷脂酰胆碱中10 - 20 mol%的甾醇相当。然而，DMPA中胆固醇的取向和分子序参数与二肉豆蔻酰磷脂酰胆碱中的相似。
