Lepore L S, Ellena J F, Cafiso D S
Department of Chemistry, University of Virginia, Charlottesville 22901.
Biophys J. 1992 Mar;61(3):767-75. doi: 10.1016/S0006-3495(92)81881-7.
13C NMR spin-lattice relaxation (T1) rates and 13C-1H nuclear Overhauser effects (NOEs) were measured in an identical fashion in two lipid preparations having dramatically different curvatures. The T1 times that were obtained at four magnetic field strengths were fit along with the NOEs to simple models for lipid molecular dynamics. The results indicate that phospholipid chain ordering and dynamics are virtually identical in small and large unilamellar vesicles at the time scales sampled by these 13C-NMR studies. The order parameters and reorientational correlation times that characterize the amplitudes and rates of internal acyl chain motions were equal within experimental error for the methylene segments in the middle of the chains. The only significant differences in order parameters and correlation times between the two vesicle types were small and appeared at the ends of the acyl chains. At the carbonyl end the order was slightly higher in small vesicles than large vesicles, and at the methyl end the order was slightly lower for small vesicles. This indicates that in the more planar systems the acyl chains exhibit a slightly flatter order profile than in more highly curved membranes. The use of the same experimental approach in both small and large vesicle systems provided a more reliable and accurate assessment of the effect of curvature on molecular order than has been previously obtained.
在两种曲率差异极大的脂质制剂中，以相同方式测量了¹³C NMR自旋晶格弛豫（T1）速率和¹³C-¹H核Overhauser效应（NOE）。在四个磁场强度下获得的T1时间与NOE一起拟合到脂质分子动力学的简单模型中。结果表明，在这些¹³C-NMR研究采样的时间尺度上，小单层囊泡和大单层囊泡中的磷脂链排序和动力学几乎相同。表征内部酰基链运动幅度和速率的序参数和重取向相关时间在实验误差范围内，对于链中间的亚甲基段是相等的。两种囊泡类型在序参数和相关时间上的唯一显著差异很小，且出现在酰基链的末端。在羰基末端，小囊泡中的有序度略高于大囊泡，而在甲基末端，小囊泡中的有序度略低。这表明在更平面的系统中，酰基链呈现出比在曲率更高的膜中略平的有序分布。在小囊泡和大囊泡系统中使用相同的实验方法，比以前获得的结果更可靠、准确地评估了曲率对分子有序度的影响。
