Mortensen K, Pfeiffer W, Sackmann E, Knoll W
Physics Department, Rise National Laboratory, Riskilde, Denmark.
Biochim Biophys Acta. 1988 Nov 22;945(2):221-45. doi: 10.1016/0005-2736(88)90485-3.
Small-angle neutron scattering has been used to study structural features of lamellar bilayer membranes of dimyristoylphosphatidylcholine (DMPC) and DMPC mixed with various amount of cholesterol. The studies were recorded at a fixed hydration level of 17% 2H2O, i.e. just below saturation. Bragg reflections gives information on the ripple structure and on the bilayer periodicity. The crystalline Lc phase, which was stabilized after long time storage at low temperature, exhibits major small angle scattering when cholesterol is mixed into the membrane. The intermediate P beta' gel-phase, which is characteristic by the rippled structure, is dramatically stabilized by the introduction of cholesterol. The ripple structure depends significantly both on the cholesterol content and on the temperature. At high temperatures, T greater than 15 degrees C, the inverse ripple periodicity varies basically linearly with cholesterol content, and approach zero (i.e. periodicity goes to infinite) at 20 mol% cholesterol, approximately. At lower temperatures the correlation is more complex. The data indicate additional phase boundaries below 2 mol% and at approx. 8 mol%. Secondary rippled structures are observed in the low temperature L beta'-phase for cholesterol content below approx. 8 mol%. The data gives detailed insight into the phosphatidylcholine cholesterol phase diagram, which is discussed on the basis of a simple model in which the cholesterol complexes are fixed to the defect stripes of the rippled structure.
小角中子散射已被用于研究二肉豆蔻酰磷脂酰胆碱（DMPC）以及与不同量胆固醇混合的DMPC的层状双分子层膜的结构特征。这些研究是在17% 2H2O的固定水合水平下记录的，即略低于饱和水平。布拉格反射给出了关于波纹结构和双分子层周期性的信息。在低温下长时间储存后稳定的结晶Lc相，当胆固醇混入膜中时会表现出主要的小角散射。具有波纹结构特征的中间Pβ'凝胶相通过引入胆固醇而显著稳定。波纹结构在很大程度上取决于胆固醇含量和温度。在高温下，T大于15摄氏度，反波纹周期性基本随胆固醇含量线性变化，在约20摩尔%胆固醇时接近零（即周期性变为无穷大）。在较低温度下，相关性更为复杂。数据表明在2摩尔%以下和约8摩尔%处存在额外的相界。在胆固醇含量低于约8摩尔%的低温Lβ'相中观察到二级波纹结构。这些数据深入洞察了磷脂酰胆碱 - 胆固醇相图，该相图基于一个简单模型进行讨论，在该模型中胆固醇复合物固定在波纹结构的缺陷条纹上。
