二棕榈酰磷脂酰胆碱/豆固醇脂质体液态有序相的结构性质:同步辐射X光衍射研究

摘要

用同步辐射小角和宽角X光衍射实验技术研究了由二棕榈酰磷脂酰胆碱(DPPC)和豆固醇所形成的脂质体的液态有序相的结构性质.结果表明液态有序相的小角X光衍射d值(d-spacing)随着固醇温度和浓度的变化仅有微小的改变.与凝胶相及液晶相的宽角X光衍射d值相比,液态有序相的宽角X光衍射d值有更宽的变化范围,在30-52 ℃的温度范围内,液态有序相的宽角X光衍射d值从0.422 nm变化到0.460 nm.电子云密度计算表明液态有序相的脂双层厚度和水层厚度都要大于与之平衡共存的液晶相的脂双层厚度和水层厚度.电子云密度计算结果还表明液态有序相的脂双层厚度随温度升高而降低.本研究结果对于从定量的角度认识生物膜的相态及深入认识生物膜中的有序结构具有重要意义.%The properties of the liquid ordered (L(.)) phase of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/stigmasterol liposomes were investigated using synchrotron small-angle and wide-angle X-ray diffraction techniques.The lamellar repeat distance of the L.phase,derived from small-angle X-ray scattering experiments,changes slightly with sterol concentration and tamperature.While the d-spacings of the acyl chains,evaluated from wide-angle X-ray scattering data,show a much broader range than those of the gel and liquid-crystal phases,varying from 0.422 to 0.460 nm when the temperature increases from 30 to 52 ℃.The electron density profiles show that the bilayer thickness and the water-layer thickness of the liquid-ordered phase are larger than that of the liquid-crystal phase,and the bilayer thickness of the liquid-ordered phase decreases with increasing temperature.The results of this study are of help in understanding the phase state and the ordered structure of biomembranes.