Chachaty C, Rainteau D, Tessier C, Quinn P J, Wolf C
Universite Paris 6, INSERM U538, Paris, France.
Biophys J. 2005 Jun;88(6):4032-44. doi: 10.1529/biophysj.104.054155. Epub 2005 Mar 11.
The long-range and molecular orders and dynamics in codispersions of egg sphingomyelin-cholesterol have been investigated by synchrotron x-ray diffraction and electron spin resonance using phosphatidylcholine spin-labeled at several positions on the sn-2 chain. Mixtures containing 0, 17, 33, 41, 50 mol% cholesterol exhibited a single phase by x-ray diffraction methods. The temperature dependence of the d-spacing between 20 and 50 degrees C is attenuated with increasing proportions of cholesterol, becoming invariant for cholesterol contents of 41 and 50 mol% on completion of the liquid-ordered phase. Electron spin resonance revealed two sites for 17 and 33 mol% cholesterol. One site is highly ordered and the other is less ordered than the fluid phase of pure sphingomyelin as shown by the molecular and the intramolecular order parameters reflecting the segmental motions of the probe. The two-sites exchange rate indicates a mean lifetime of the sites of approximately 0.1 micros during which the lipid displacement is approximately 1 nm. The short lifetime of the sites probed by ESR and the single phase detected by x-ray diffraction support in this binary mixture, the building up of the Lo phase by a progressive accumulation of randomly distributed sphingomyelin-cholesterol condensed complexes rather than by diffusional exchange between extended domains.
通过同步加速器X射线衍射和电子自旋共振，使用在sn-2链上多个位置进行自旋标记的磷脂酰胆碱，研究了鸡蛋鞘磷脂 - 胆固醇共分散体系中的长程和分子有序性及动力学。通过X射线衍射方法，含有0、17、33、41、50摩尔％胆固醇的混合物呈现单相。在20至50摄氏度之间，d间距的温度依赖性随着胆固醇比例的增加而减弱，在液体有序相完成时，对于41和50摩尔％的胆固醇含量变得不变。电子自旋共振揭示了17和33摩尔％胆固醇存在两个位点。如反映探针片段运动的分子和分子内序参数所示，一个位点高度有序，另一个位点的有序程度低于纯鞘磷脂的流体相。两位点交换速率表明位点的平均寿命约为0.1微秒，在此期间脂质位移约为1纳米。由ESR探测的位点的短寿命和由X射线衍射检测到的单相支持了在这种二元混合物中，Lo相是通过随机分布的鞘磷脂 - 胆固醇凝聚复合物的逐步积累而形成的，而不是通过扩展域之间的扩散交换形成的。
