Lipari G, Szabo A
Biophys J. 1980 Jun;30(3):489-506. doi: 10.1016/S0006-3495(80)85109-5.
The theory of fluorescent emission anisotropy [r(t)] of a cylindrical probe in a membrane suspension is developed. It is shown, independent of any model, that the limiting anisotropy [r(infinity)] is proportional to the square to the order parameter of the probe. The order parameter determines the first nontrivial term in the expansion of the equilibrium orientational distribution function of the probe in a series of Legendre polynomials. Following Kinosita, Kawato, and Ikegami, the motion of the probe is described as diffusion ("wobbling") within a cone of semiangle theta 0. Within the framework of this model, an accurate single-exponential approximation for r(t) is considered. An analytic expression relating the effective relaxation time, which appears in the above approximation, to theta 0 and the diffusion coefficient for wobbling is derived. The model is generalized to the situation where the probe is attached to a macromolecule whose motion cannot be neglected on the time scale of the fluorescence experiment. Finally, by exploiting the formal similarity between the theory of fluorescence depolarization and 13C-NMR dipolar relaxation, expressions for T1, T2, and the nuclear Overhauser enhancement are derived for a protonated carbon which is nonrigidly attached to a macromolecule and undergoes librational motion described as diffusion on a spherical "cap" of semiangle theta 0.
本文推导了膜悬浮液中圆柱形探针的荧光发射各向异性[r(t)]理论。结果表明，在不依赖任何模型的情况下，极限各向异性[r(∞)]与探针序参量的平方成正比。序参量决定了探针平衡取向分布函数在勒让德多项式级数展开中的首个非平凡项。按照木下、川登和池上的方法，将探针的运动描述为在半角为θ0的圆锥体内的扩散（“摆动”）。在此模型框架内，考虑了对r(t)的精确单指数近似。推导了上述近似中出现的有效弛豫时间与θ0以及摆动扩散系数之间的解析表达式。该模型被推广到探针附着于大分子的情况，在荧光实验的时间尺度上，大分子的运动不可忽略。最后，通过利用荧光去极化理论与13C - NMR偶极弛豫之间的形式相似性，推导了对于非刚性附着于大分子并经历如在半角为θ0的球形“帽”上扩散所描述的 librational 运动的质子化碳的T1、T2和核Overhauser增强的表达式。
