不同固醇与DPPC二元体系的液态有序相

应用同步辐射X射线衍射和差示扫描量热法研究了由不同结构的固醇(胆固醇、脱氢胆固醇、豆固醇、谷固醇、麦角固醇以及固醇核)和二棕榈酰磷脂酰胆碱(DPPC)二元体系形成的液态有序相. 研究表明, 胆固醇比植物固醇(豆固醇和谷固醇)和真菌固醇(麦角固醇)能更有效地与DPPC形成液态有序相(Lo); 有胆固醇或者脱氢胆固醇参与的液态有序相能够在较宽的温度范围内保持稳定, 而由植物固醇和真菌固醇参与的液态有序相对温度有较强的依赖性, 在DPPC主相变温度附近有明显的热致相变过程, 因此这一液态有序相应该进一步区分为Loβ和Loα相. 研究结果有助于阐明固醇尾链在液态有序相以及脂筏中的作用, 也有助于理解在进化过程中动物细胞膜为何选择胆固醇作为主要固醇.

Liquid Ordered Phase of Binary Mixtures Containing Dipalmitoylphosphatidylcholine and Sterols

The effect of cholesterol,desmosterol,stigrnasterol,sitosterol,ergosterol,and androsterol on the phase behavior of aqueous dispersions of dipalmitoylphosphatidylcholine(DPPC) was studied to understand the role of the side chain in the formation of ordered phases of the type observed in membrane rafts.Thermotropic changes in the structure of mixed dispersions and transition enthalpies were examined by synchrotron X-ray diffraction(XRD) and differential scanning calorimetry(DSC).The observations indicated that cholesterol was more efficient than phytosterols (stigmasterol and sitosterol)or ergosterol in its interaction with DPPC to form the liquid ordered phase(Lo).The Loreduced by cholesterol or desmosterol was stable over a wide temperature range,whereas,the liquid ordered phase contaimng phytostemls or ergosterol was profoundly dependent on temperature,which should be distinguished as Loβ and Loα,representing the phases below and above the main transition temperature.The characteristies in forming ordered structures of cholesterol and other sterols imply that the evolution may have selected cholesterol as the most efficient sterol for animals to form rafts in their cell membranes.