磷脂双分子层中磷酸基团的动力学。一项磷-31角相关核自旋弛豫时间研究。
Dynamics of the phosphate group in phospholipid bilayers. A 31P angular dependent nuclear spin relaxation time study.
作者信息
Milburn M P, Jeffrey K R
机构信息
Guelph-Waterloo Program for Graduate Work in Physics, University of Guelph, Ontario, Canada.
出版信息
Biophys J. 1989 Sep;56(3):543-9. doi: 10.1016/S0006-3495(89)82701-8.
To understand 31P relaxation processes and hence molecular dynamics in the phospholipid multilayer it is important to measure the dependence of the 31P spin-lattice relaxation time on as many variables as the physical system allows. Such measurements of the 31P spin-lattice relaxation rate have been reported both as a function of Larmor frequency and temperature for egg phosphatidylcholine liposomes (Milburn, M.P., and K.R. Jeffrey. 1987. Biophys. J. 52:791-799). In principle, the spin-lattice relaxation rate in an anisotropic environment such as a bilayer will be a function of the angle between the bilayer normal and the magnetic field. However, the measurement of this angular dependence has not been possible because the rapid (on the time-scale of the spin-lattice relaxation rate) diffusion of the lipid molecules over the curved surface of the liposome average this dependence (Milburn, M.P., and K.R. Jeffrey. 1987. Biophys. J. 52:791-799; Brown, M.F., and J.H. Davis. 1981. Chem. Phys. Lett. 79:431-435). This paper reports the results of the measurement of the 31P spin-lattice relaxation rate as a function of this angle, beta', (the angle between the bilayer normal and the external magnetic field) using samples oriented between glass plates. These measurements were made at high field (145.7 MHz) where the spin-lattice relaxation processes are dominated by the chemical shielding interaction (Milburn, M.P., and K.R. Jeffrey. 1987. Biophys. J. 52:791-799). A model of molecular motion that includes a fast axially symmetric rotation of the phosphate group (tau i approximately 10(-9) s) and a wobble of the head group tilt with respect to this rotation axis has been used to describe both the angular dependence of the spin-lattice relaxation and the spectral anisotropy. Cholesterol is seen to have a negligible effect on the motional properties of the phospholipid phosphate segment as measured by the orientation dependence of the spin-lattice relaxation.
为了理解磷脂多层膜中的³¹P弛豫过程以及分子动力学，在物理系统允许的范围内尽可能多地测量³¹P自旋 - 晶格弛豫时间对各种变量的依赖性非常重要。对于鸡蛋磷脂酰胆碱脂质体，已经报道了³¹P自旋 - 晶格弛豫率作为拉莫尔频率和温度的函数的此类测量结果（米尔本，M.P.，和K.R.杰弗里。1987年。《生物物理杂志》52:791 - 799）。原则上，在诸如双层这样的各向异性环境中，自旋 - 晶格弛豫率将是双层法线与磁场之间夹角的函数。然而，由于脂质分子在脂质体曲面上的快速（在自旋 - 晶格弛豫率的时间尺度上）扩散使这种依赖性平均化，所以无法测量这种角度依赖性（米尔本，M.P.，和K.R.杰弗里。1987年。《生物物理杂志》52:791 - 799；布朗，M.F.，和J.H.戴维斯。1981年。《化学物理快报》79:431 - 435）。本文报道了使用夹在玻璃板之间的取向样品测量³¹P自旋 - 晶格弛豫率作为该角度β′（双层法线与外部磁场之间的夹角）的函数的结果。这些测量是在高场（145.7 MHz）下进行的，在该高场中自旋 - 晶格弛豫过程主要由化学屏蔽相互作用主导（米尔本，M.P.，和K.R.杰弗里。1987年。《生物物理杂志》52:791 - 799）。一个分子运动模型被用来描述自旋 - 晶格弛豫的角度依赖性和光谱各向异性，该模型包括磷酸基团的快速轴对称旋转（τi约为10⁻⁹ s）以及头部基团相对于该旋转轴的摆动。通过自旋 - 晶格弛豫的取向依赖性测量发现，胆固醇对磷脂磷酸片段的运动性质影响可忽略不计。
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