Ipsen J H, Karlström G, Mouritsen O G, Wennerström H, Zuckermann M J
Department of Structural Properties of Materials, Technical University of Denmark, Lyngby.
Biochim Biophys Acta. 1987 Nov 27;905(1):162-72. doi: 10.1016/0005-2736(87)90020-4.
A thermodynamic and a microscopic interaction model are proposed to describe the phase equilibria in the phosphatidylcholine-cholesterol system. The model calculations allow for a solid phase with conformationally ordered acyl chains and liquid phases with conformationally ordered as well as disordered chains. The resulting phase diagram is in excellent agreement with the experimental phase diagram for dipalmitoylphosphatidylcholine bilayers with cholesterol as determined by a recent NMR and calorimetry study. It is thus demonstrated that the phase behaviour of phosphatidylcholine-cholesterol mixtures can be rationalized using only a few basic assumptions: (i) Cholesterol interacts favourably with phosphatidylcholine chains in an extended conformation, (ii) the main transition of pure phosphatidylcholine bilayers takes place in terms of translational variables as well acyl-chain conformational variables, and (iii) cholesterol disturbs the translational order in the crystalline (gel) state of phosphatidylcholine. These results suggest that the occurrence of specific phosphatidylcholine-cholesterol complexes is not implied by the experimental thermodynamic data.
提出了一种热力学和微观相互作用模型来描述磷脂酰胆碱 - 胆固醇系统中的相平衡。该模型计算考虑了具有构象有序酰基链的固相以及具有构象有序和无序链的液相。所得相图与最近通过核磁共振和量热法研究确定的含胆固醇的二棕榈酰磷脂酰胆碱双层的实验相图高度吻合。因此表明，仅使用几个基本假设就可以解释磷脂酰胆碱 - 胆固醇混合物的相行为：（i）胆固醇与伸展构象的磷脂酰胆碱链有利地相互作用，（ii）纯磷脂酰胆碱双层的主要转变在平移变量以及酰基链构象变量方面发生，并且（iii）胆固醇扰乱磷脂酰胆碱晶体（凝胶）状态下的平移有序。这些结果表明，实验热力学数据并不意味着存在特定的磷脂酰胆碱 - 胆固醇复合物。
