Watts A, Harlos K, Marsh D
Biochim Biophys Acta. 1981 Jul 6;645(1):91-6. doi: 10.1016/0005-2736(81)90515-0.
X-ray diffraction studies have been performed, as a function of water content, on dipalmitoyl phosphatidylglycerol bilayers, both in the charged state at pH 8.0 and in the protonated state at pH 1.5, using buffers of 1.5 M salt concentration. Measurements were made at 20 degrees C, and the high-angle reflections indicated that the bilayers were in the ordered phase at both pH values. Lamellar diffractions were observed under all conditions studied. THe lamellar repeat reached a limiting value of 62.4 A (6.24 nm) at a water/lipid ratio of 0.24 at pH 8.0, and a limiting value of 67.3 A (6.73 nm) at a water/lipid ratio of 0.22 at pH 1.5. The area per lipid molecule in the plane of the bilayer, deduced from the bilayer thickness and the lipid partial specific volume, is 48 A2 (0.48 nm2) at pH 8.0 and 37 A2 (0.37 nm2) at pH 1.5. The area per molecule in the plane perpendicular to the chain axes, deduced from the X-ray short spacings, is 40.5 A2 (0.405 nm2) at pH 8.0 and 39.2 A2 (0.392 nm2) at pH 1.5. Thus the lipid molecules are tilted by approx. 30 degrees relative to the bilayer normal at pH 8.0, but are essentially untilted at pH 1.5.
利用盐浓度为1.5M的缓冲液，在20摄氏度下，对处于pH 8.0的带电状态和pH 1.5的质子化状态的二棕榈酰磷脂酰甘油双层膜进行了X射线衍射研究，研究内容为水含量的函数。高角度反射表明，在这两个pH值下双层膜均处于有序相。在所研究的所有条件下均观察到层状衍射。在pH 8.0时，水/脂质比为0.24时，层状重复间距达到极限值62.4 Å（6.24 nm）；在pH 1.5时，水/脂质比为0.22时，层状重复间距达到极限值67.3 Å（6.73 nm）。根据双层膜厚度和脂质偏比容推导出的双层膜平面内每个脂质分子的面积，在pH 8.0时为48 Ų（0.48 nm²），在pH 1.5时为37 Ų（0.37 nm²）。根据X射线短间距推导出的垂直于链轴平面内每个分子的面积，在pH 8.时为40.5 Ų（0.405 nm²），在pH 1.5时为39.2 Ų（0.392 nm²）。因此，在pH 8.0时，脂质分子相对于双层膜法线倾斜约30度，但在pH 1.5时基本不倾斜。
