Parasassi T, Di Stefano M, Loiero M, Ravagnan G, Gratton E
Istituto di Medicina Sperimentale, CNR, 00137 Rome, Italy.
Biophys J. 1994 Mar;66(3 Pt 1):763-8. doi: 10.1016/s0006-3495(94)80852-5.
The effect of cholesterol on the gel, the liquid-crystalline, and mixed phospholipid phases has been studied using the fluorescence properties of 2-dimethylamino-6-lauroylnaphthalene (Laurdan). Laurdan sensitivity to the polarity and to the dynamics of its environment reveals that cholesterol affects phospholipid bilayers in the gel phase by expelling water and by increasing the amount of dipolar relaxation. In the liquid-crystalline phase, the effect of cholesterol is a reduction of both water concentration and amount of dipolar relaxation. Detailed studies of Laurdan excitation and emission spectral contours as a function of cholesterol concentration show that there are some cholesterol concentrations at which Laurdan spectral properties changes discontinuously. These peculiar cholesterol concentrations are in agreement with recent observations of other workers showing the formation of local order in the liquid-crystalline phase of phospholipids upon addition of phospholipid derivatives of pyrene. A local organization of phospholipids around cholesterol molecule seems to be produced by the presence of peculiar concentrations of cholesterol itself. This local organization is stable enough to be observed during the excited state lifetime of Laurdan of approximately 5-6 ns.
利用2-二甲基氨基-6-月桂酰萘（Laurdan）的荧光特性，研究了胆固醇对凝胶相、液晶相和混合磷脂相的影响。Laurdan对其环境的极性和动力学的敏感性表明，胆固醇通过排出水分和增加偶极弛豫量来影响凝胶相中的磷脂双层。在液晶相中，胆固醇的作用是降低水浓度和偶极弛豫量。对Laurdan激发和发射光谱轮廓随胆固醇浓度变化的详细研究表明，存在一些胆固醇浓度，在这些浓度下Laurdan光谱特性会发生不连续变化。这些特殊的胆固醇浓度与其他研究人员最近的观察结果一致，即添加芘的磷脂衍生物后，磷脂液晶相中会形成局部有序结构。胆固醇分子周围磷脂的局部组织似乎是由胆固醇本身的特殊浓度产生的。这种局部组织足够稳定，在Laurdan约5-6纳秒的激发态寿命期间可以观察到。
