Wassall S R
Department of Physics, Indiana University-Purdue University Indianapolis, 46202-3273, USA. ieaz
Biophys J. 1996 Nov;71(5):2724-32. doi: 10.1016/S0006-3495(96)79463-8.
Water diffusion in the lamellar phase of egg phosphatidylcholine (egg PC)-water was studied by 1H NMR using the pulsed field gradient-spin echo method. The curvature of diffusion plots obtained with egg PC-water mixtures indicates that water diffusion is highly anisotropic with respect to lipid lamellae. This was confirmed by measurements made on macroscopically aligned egg PC-water as a function of orientation that categorically establish DII/DI >> .1, where the respective subscripts refer to parallel and perpendicular to the lipid bilayer. A smooth, monotonic dependence on water concentration was observed for water diffusion in aligned egg PC-water, varying at 25 degrees C from DII = 1.2 x 10(-10) m2 s 1 at n = 4.9 mol water/lipid to DII = 4.0 x 10(-10) m2 s-1 at n = 18.6 mol water/lipid. The diffusion is approximately a factor of 10 slower than in pure water because of water binding and restriction to translational motion within the aqueous layer. No evidence for a sudden drop in water diffusion coefficient at a specific water content, as previously reported with egg PC-water mixtures (Lange and Gary Bobo. 1974. J. Gen. Physiol 63:690-706), was detected. A morphological reorganization of lamellar domains, which in random orientational distribution comprise lipid-water mixtures, is the likely explanation. The study of aligned lipid-water systems is manifestly preferable.
采用脉冲场梯度自旋回波法，通过1H NMR研究了鸡蛋磷脂酰胆碱（egg PC）-水层状相中水的扩散。用egg PC-水混合物得到的扩散图的曲率表明，水的扩散相对于脂质层具有高度各向异性。这一点通过对宏观排列的egg PC-水进行测量得到证实，测量结果表明，随着取向的变化，DII/DI >> 0.1，其中相应的下标分别表示平行和垂直于脂质双层。在排列的egg PC-水中观察到水扩散对水浓度有平滑、单调的依赖性，在25℃时，水扩散系数从n = 4.9 mol水/脂质时的DII = 1.2×10-10 m2 s-1变化到n = 18.6 mol水/脂质时的DII = 4.0×10-10 m2 s-1。由于水的结合以及对水层内平移运动的限制，扩散速度比在纯水中慢约10倍。未检测到如先前报道的egg PC-水混合物（Lange和Gary Bobo，1974年，《普通生理学杂志》63:690-706）在特定水含量时水扩散系数突然下降的证据。层状结构域的形态重组可能是原因，层状结构域在随机取向分布中构成脂质-水混合物。显然，对排列的脂质-水系统进行研究更为可取。
