Scott H L
Department of Physics, Oklahoma State University, Stillwater 74078-0444.
Biophys J. 1991 Feb;59(2):445-55. doi: 10.1016/S0006-3495(91)82238-X.
Results of Monte Carlo calculations of order parameter profiles of lipid chains interacting with cholesterol are presented. Cholesterol concentrations in the simulations are sufficiently large that it is possible to analyze profiles for chains which are near neighbors of two or more cholesterol molecules, chains which are neighbors to a single cholesterol, and chains which are not near any cholesterol molecules. The profiles, show that cholesterol acts to significantly decrease the ability of neighboring chains to undergo trans-gauche isomeric rotations, although these chains are not all forced into all-trans conformations. The effect is significantly greater for chains which are neighbors to more than one cholesterol. The Monte Carlo results are next used as a guide to develop a theoretical model for lipid-cholesterol mixtures. The properties of this model and the phase diagram which it predicts are described. The phase diagram is then compared with experimentally determined phase diagrams. The model calculations and the computer simulations upon which they are based yield a molecular mechanism for several of the observed phases exhibited by lipid-cholesterol mixtures. The theoretical model predicts that at low temperatures the system should exhibit solid phase immiscibility.
给出了与胆固醇相互作用的脂链序参量分布的蒙特卡罗计算结果。模拟中的胆固醇浓度足够高，以至于能够分析与两个或更多胆固醇分子相邻的链、与单个胆固醇相邻的链以及不与任何胆固醇分子相邻的链的分布情况。这些分布表明，胆固醇显著降低了相邻链进行反式-顺式异构旋转的能力，尽管这些链并非都被迫形成全反式构象。对于与多个胆固醇相邻的链，这种影响更为显著。接下来，将蒙特卡罗结果用作指导来开发脂类-胆固醇混合物的理论模型。描述了该模型的性质及其预测的相图。然后将相图与实验测定的相图进行比较。模型计算及其所基于的计算机模拟为脂类-胆固醇混合物所呈现的几种观察到的相提供了一种分子机制。理论模型预测，在低温下系统应表现出固相不混溶性。
