Dufourc E J, Mayer C, Stohrer J, Althoff G, Kothe G
Centre de Recherche Paul Pascal, CNRS, Pessac France.
Biophys J. 1992 Jan;61(1):42-57. doi: 10.1016/S0006-3495(92)81814-3.
Phospholipid head group dynamics have been studied by pulsed phosphorus-31 nuclear magnetic resonance (31P-NMR) of unoriented and macroscopically aligned dimyristoylphosphatidylcholine model membranes in the temperature range, 203-343 K. Lineshapes and echo intensities have been recorded as a function of interpulse delay times, temperature and macroscopic orientation of the bilayer normal with respect to the magnetic field. The dipolar proton-phosphorus (1H-31P) contribution to the transverse relaxation time, T2E, and to lineshapes was eliminated by means of a proton spin-lock sequence. In case of longitudinal spin relaxation, T1Z, the amount of dipolar coupling was evaluated by measuring the maximum nuclear Overhauser enhancement. Hence, the results could be analyzed by considering chemical shift anisotropy as the only relaxation mechanism. The presence of various minima both in T1Z and T2E temperature plots as well as the angular dependence of these relaxation times allowed description of the dynamics of the phosphate head group in the 31P-NMR time window, by three different motional classes, i.e., intramolecular, intermolecular and collective motions. The intramolecular motions consist of two hindered rotations and one free rotation around the bonds linking the phosphate head group to the glycerol backbone. These motions are the fastest in the hierarchy of time with correlation times varying from less than 10(-12) to 10(-6) s in the temperature range investigated. The intermolecular motions are assigned to phospholipid long axis rotation and fluctuation. They have correlation times ranging from 10(-11) s at high temperatures to 10(-3) s at low temperatures. The slowest motion affecting the 31P-NMR observables is assigned to viscoelastic modes, i.e., so called order director fluctuations and is only detected at high temperatures, above the main transition in pulse frequency dependent T2ECP experiments. Comprehensive analysis of the phosphate head group dynamics is achieved by a dynamic NMR model based on the stochastic Liouville equation. In addition to correlation times, this analysis provides activation energies and order parameters for the various motions, and a value for the bilayer elastic constant.
通过对温度范围为203 - 343K的未取向和宏观取向的二肉豆蔻酰磷脂酰胆碱模型膜进行脉冲磷-31核磁共振（31P-NMR）研究了磷脂头部基团动力学。记录了线形和回波强度作为脉冲间隔时间、温度以及双层法线相对于磁场的宏观取向的函数。通过质子自旋锁定序列消除了偶极质子 - 磷（1H - 31P）对横向弛豫时间T2E和线形的贡献。在纵向自旋弛豫T1Z的情况下，通过测量最大核Overhauser增强来评估偶极耦合的量。因此，结果可以通过将化学位移各向异性视为唯一的弛豫机制来进行分析。T1Z和T2E温度图中存在各种最小值以及这些弛豫时间的角度依赖性，使得能够通过三种不同的运动类别，即分子内、分子间和集体运动，来描述31P-NMR时间窗口中磷酸头部基团的动力学。分子内运动由围绕连接磷酸头部基团与甘油主链的键的两次受阻旋转和一次自由旋转组成。这些运动在时间层次结构中是最快的，在所研究的温度范围内相关时间从小于10^(-12)秒到10^(-6)秒不等。分子间运动归因于磷脂长轴旋转和波动。它们的相关时间范围从高温下的10^(-11)秒到低温下的10^(-3)秒。影响31P-NMR可观测值的最慢运动归因于粘弹性模式，即所谓的有序指向矢波动，并且仅在高温下，即在脉冲频率依赖的T2ECP实验中的主要转变温度以上才能检测到。通过基于随机刘维尔方程的动态NMR模型实现了对磷酸头部基团动力学的综合分析。除了相关时间外，该分析还提供了各种运动的活化能和序参量，以及双层弹性常数的值。
