Tang D, Wieb van der Meer B, Chen S Y
Department of Physics and Astronomy, Western Kentucky University, Bowling Green 42101, USA.
Biophys J. 1995 May;68(5):1944-51. doi: 10.1016/S0006-3495(95)80371-1.
Cholesterol/dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles were studied by steady-state fluorescence using diphenylhexatriene (DPH) as a probe. A series of dips were found in the plot of DPH fluorescence intensity versus cholesterol concentration at certain specific cholesterol concentrations. This observation indicates that there are dominant domains in which cholesterol molecules are regularly distributed on a hexagonal superlattice in the acyl chain matrix of DMPC at critical cholesterol concentrations. These concentrations can be predicted by an equation or a mathematical series, except the one at 33 mol %. These dips of DPH fluorescence intensity are temperature dependent. The excellent agreement between experimental data and calculated values as well as similar previous findings of dips and/or kinks in the excimer-over-monomer fluorescence in pyrenephosphatidylcholine/phospholipid mixtures confirm our conclusion about lateral organizations of cholesterol and acyl lipid chains in cholesterol/phospholipid multilamellar vesicles. The regular distribution model at critical concentration is consistent with the phase diagram of cholesterol/DMPC. Using the model of regular distribution, the physical origin of the liquid-disordered (Ld) phase, liquid-ordered phase (Lo), and coexistence of liquid-disordered phase and Lo phase (Lo + Ld) is discussed on the molecular level.
使用二苯基己三烯（DPH）作为探针，通过稳态荧光对胆固醇/二肉豆蔻酰磷脂酰胆碱（DMPC）多层囊泡进行了研究。在特定的胆固醇浓度下，发现DPH荧光强度与胆固醇浓度的关系图中存在一系列下降。这一观察结果表明，在临界胆固醇浓度下，在DMPC酰基链基质中的六方超晶格上存在胆固醇分子规则分布的主导区域。除了33摩尔%处的浓度外，这些浓度可以通过一个方程或一个数学级数来预测。DPH荧光强度的这些下降与温度有关。实验数据与计算值之间的良好一致性以及芘磷脂酰胆碱/磷脂混合物中准分子对单体荧光中先前类似的下降和/或扭结发现，证实了我们关于胆固醇/磷脂多层囊泡中胆固醇和酰基脂链横向组织的结论。临界浓度下的规则分布模型与胆固醇/DMPC的相图一致。利用规则分布模型，在分子水平上讨论了液相无序（Ld）相、液相有序相（Lo）以及液相无序相和Lo相共存（Lo + Ld）的物理起源。
