van Ginkel G, van Langen H, Levine Y K
Department of Molecular Biophysics, State University of Utrecht, The Netherlands.
Biochimie. 1989 Jan;71(1):23-32. doi: 10.1016/0300-9084(89)90127-2.
Quantitative analysis of time-resolved anisotropy measurements of DPH or TMA-DPH in lipid vesicles yields more than one mathematically correct solution. The solutions differ with respect to the average orientation and to the reorientational dynamics of the probe molecules in the bilayer. This leads to quite opposite results regarding the effects of cholesterol on membrane fluidity. One solution predicts an increase in fluidity, the other a decrease. Angle-resolved fluorescence depolarization (AFD) measurements of probes in oriented lipid bilayers enable determination of the average orientation of the probes in the bilayer and, if the fluorescence decay function is known, of the reorientational dynamics. Analysis of AFD measurements of DPH and TMA-DPH show that increasing unsaturation leads to a decrease in molecular order and a decrease in reorientational dynamics (= fluidity) of the probes. At temperatures above the phase transition of the lipids, the addition of cholesterol causes an increase in molecular order and an increase in reorientational dynamics (= fluidity). The plant sterol stigmaterol, which is structurally closely related to cholesterol, has different effects than cholesterol. The effects vary with the structure of the surrounding lipids. The membrane fluidity concept as it was originally proposed by Chapman attempts to describe the structural and dynamic properties of lipids in a membrane using one single parameter indicated as 'membrane fluidity'. Our results show that it is necessary to distinguish between structural parameters describing molecular order and motion parameters describing molecular dynamics, thus supporting a similar suggestion by Seelig and Seelig. In order to be useful, the membrane fluidity concept has to be limited to the parameters describing molecular dynamics.
对脂质体中DPH或TMA - DPH的时间分辨各向异性测量进行定量分析会得出不止一个数学上正确的解。这些解在探针分子在双层膜中的平均取向和重取向动力学方面存在差异。这导致在胆固醇对膜流动性的影响方面得出完全相反的结果。一种解预测流动性增加，另一种解预测流动性降低。对取向脂质双层中探针进行角度分辨荧光去极化（AFD）测量能够确定探针在双层膜中的平均取向，并且如果已知荧光衰减函数，还能确定重取向动力学。对DPH和TMA - DPH的AFD测量分析表明，不饱和度增加会导致分子有序性降低以及探针的重取向动力学（=流动性）降低。在高于脂质相变温度时，添加胆固醇会导致分子有序性增加以及重取向动力学（=流动性）增加。植物甾醇豆甾醇在结构上与胆固醇密切相关，但其作用与胆固醇不同。其作用随周围脂质的结构而变化。最初由查普曼提出的膜流动性概念试图用一个单一参数“膜流动性”来描述膜中脂质的结构和动态特性。我们的结果表明，有必要区分描述分子有序性的结构参数和描述分子动力学的运动参数，从而支持塞利格和塞利格提出的类似建议。为了有用，膜流动性概念必须限于描述分子动力学的参数。
