Milburn M P, Jeffrey K R
Guelph-Waterloo Program for Graduate Work in Physics, University of Guelph, Ontario, Canada.
Biophys J. 1990 Jul;58(1):187-94. doi: 10.1016/S0006-3495(90)82364-X.
Two recent studies have addressed the question of the dynamics of the phosphate in egg phosphatidylcholine multilayers by measurement and interpretation of 31P NMR spin-lattice relaxation. In the first (Milburn, M. P., and K. R. Jeffrey. 1987. Biophys. J. 52:791-799), the temperature dependences of the two contributions to the 31P relaxation rate, a dipolar interaction of the phosphorus with neighboring protons and a time-dependent anisotropic chemical shielding interaction were separately measured. A further study (Milburn, M. P., and K. R. Jeffrey. 1989. Biophys. J. 56:543-549) incorporated the anisotropic nature of phospholipid motions into the dynamic model of the headgroup motion by measuring the 31P spin-lattice relaxation time in oriented samples as a function of angle between the bilayer normal and the magnetic field. These angular dependent measurements were made at high field so that analysis could by made using the chemical shielding interaction because the 31P-1H dipolar interaction in phospholipid systems is complex and as such poorly understood. Nuclear Overhauser effect (NOE) studies have attempted to identify the important proton species contributing to the 31P-1H dipolar interaction (Yeagle, P. L., W. C. Hutton, C. Huang, and R. B. Martin. 1975. Biochemistry. 15:2121-2124) and despite some controversy in interpretation (Burns, R. A., R. E. Stark, D. A. Vidusek, and M. F. Roberts. 1983. Biochemistry. 22:5084-5090), it was generally agreed that the choline methyl and methylene protons are the major contributors to the 31P-1H NOE. To further understand the nature of the 31P-1H dipolar interaction, we carried out 31P-1H Transient Overhauser effect (TOE) measurements on egg phosphatidylcholine multilayers. Protons from both the lipids and water are important in understanding the TOE measurements in both D20 dispersions and H20 dispersions of egg PC. A quantitative analysis of the TOE has enabled the cross-relaxation rate between the phosphorus and the two proton types to be determined. It is suggested that these TOE experiments are a direct observation of the interaction between the phospholipid phosphate and surrounding water protons. The correlation time describing the relative motion of the phosphate group and the water molecules is on the order of 10- 11 s. The TOE measurements in phospholipid dispersions can be easily understood in terms of a straight forward model of the dipolar interaction and provide complementary information to NOE and T1 measurements.
最近的两项研究通过对³¹P NMR自旋晶格弛豫的测量和解释，探讨了鸡蛋磷脂酰胆碱多层膜中磷酸盐的动力学问题。在第一项研究中（米尔本，M. P.，和K. R. 杰弗里。1987年。《生物物理杂志》。52:791 - 799），分别测量了对³¹P弛豫率有贡献的两个因素的温度依赖性，即磷与相邻质子的偶极相互作用以及随时间变化的各向异性化学屏蔽相互作用。另一项研究（米尔本，M. P.，和K. R. 杰弗里。1989年。《生物物理杂志》。56:543 - 549）通过测量取向样品中³¹P自旋晶格弛豫时间作为双层法线与磁场之间角度的函数，将磷脂运动的各向异性性质纳入了头基运动的动力学模型。这些角度依赖性测量是在高场下进行的，以便能够利用化学屏蔽相互作用进行分析，因为磷脂体系中的³¹P - ¹H偶极相互作用很复杂，目前对此了解甚少。核Overhauser效应（NOE）研究试图确定对³¹P - ¹H偶极相互作用有重要贡献的质子种类（耶格尔，P. L.，W. C. 赫顿，C. 黄，和R. B. 马丁。1975年。《生物化学》。15:2121 - 2124），尽管在解释上存在一些争议（伯恩斯，R. A.，R. E. 斯塔克，D. A. 维杜塞克，和M. F. 罗伯茨。1983年。《生物化学》。22:5084 - 5090），但普遍认为胆碱甲基和亚甲基质子是³¹P - ¹H NOE的主要贡献者。为了进一步了解³¹P - ¹H偶极相互作用的性质，我们对鸡蛋磷脂酰胆碱多层膜进行了³¹P - ¹H瞬态Overhauser效应（TOE）测量。脂质和水中的质子对于理解鸡蛋PC在D₂O分散体和H₂O分散体中的TOE测量都很重要。对TOE的定量分析使得能够确定磷与两种质子类型之间的交叉弛豫率。有人认为，这些TOE实验是对磷脂磷酸盐与周围水质子之间相互作用的直接观察。描述磷酸基团和水分子相对运动的相关时间约为10⁻¹¹秒。磷脂分散体中的TOE测量可以根据偶极相互作用的简单模型很容易地理解，并为NOE和T₁测量提供补充信息。
