MEMBRANE CURVATURE, LIPID SEGREGATION, AND STRUCTURAL TRANSITIONS FOR PHOSPHOLIPIDS UNDER DUAL-SOLVENT STRESS
MEMBRANE CURVATURE, LIPID SEGREGATION, AND STRUCTURAL TRANSITIONS FOR PHOSPHOLIPIDS UNDER DUAL-SOLVENT STRESS
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DOI：
10.1021/bi00453a010
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发表时间：
1990-01-09
期刊：
影响因子：
2.9
通讯作者：
PARSEGIAN, VA
中科院分区：
文献类型：
--
作者：
RAND, RP;FULLER, NL;PARSEGIAN, VA
两亲分子对极性和非极性溶剂都有反应。本文用X射线衍射和渗透应力研究了由二油酰磷脂酰乙醇胺（DOPE）和二油酰磷脂酰胆碱（DOPC）混合物形成的单层膜水腔的相行为、结构尺寸和变形功随水和十四烷（td）两种溶剂浓度的变化。在没有td的情况下，大多数PE/PC混合物在过量的水中仅显示层状相;所有这些在添加过量的td时变成单一的反六方（HII）相。脂质单层的自发曲率半径R 0，表示在这些HII阶段，是允许的烃链应力由td的救济; R 0的DOPC/DOPE的比例增加。具有非常大的R 0“的混合物可以具有高于L α的水含量。在没有TD的情况下形成的阶段。水化的驱动力被理解为除了极性基团的直接水化之外，还产生大的水腔的曲率能。去除水以产生半径R <R 0的六方相的大部分工作是改变单层曲率，而不是使极性基团脱水。单一HII阶段强调有限的水或td显示几个响应。(a)分子面积在分子的极性端被压缩，在烃端被扩大。(b)对于圆形对称的水圆柱，烃链张开和极性基团压缩的程度对于在水圆柱周围沿不同方向排列的分子是不同的。(c)一个枢轴位置存在沿着磷脂分子的长度，其中发生小面积的变化，因为单层被弯曲到增加曲率。(d)通过在枢轴位置定义R 0，我们发现测量的能量与二次弯曲能量K 0/2（1/R-1/R 0）很好地拟合;拟合产生双层弯曲模量Kc =（1.2-1.7）× 1000。10-12尔格，与双层力学的测量结果一致。(e)对于脂质混合物，HII单层与R 0的强制偏离足以引起磷脂的分层，这表明DOPE/DOPC比率自我调节，使得其R 0与td或可用水量相匹配，即，曲率能量被最小化。
Amphiphiles respond both to polar and to nonpolar solvents. In this paper X-ray diffraction and osmotic stress have been used to examine the phase behavior, the structural dimensions, and the work of deforming the monolayer-lined aqueous cavities formed by mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC) as a function of the concentration of two solvents, water and tetradecane (td). In the absence of td, most PE/PC mixtures show only lamellar phases in excess water; all of these become single reverse hexagonal (HII) phases with addition of excess td. The spontaneous radius of curvature R0 of lipid monolayers, as expressed in these HII phases, is allowed by the relief of hydrocarbon chain stress by td; R0 increases with the ratio DOPC/DOPE. Mixtures with very large R0''s can have water contents higher than the L.alpha. phases that form in the absence of td. The drive for hydration is understood in terms of the curvature energy to create large water cavities in addition to direct hydration of the polar groups. Much of the work of removing water to create hexagonal phases of radius R < R0 goes into changing monolayer curvature rather than dehydrating polar groups. Single HII phases stressed by limited water or td show several responses. (a) The molecular area is compressed at the polar end of the molecule and expanded at the hydrocarbon ends. (b) For circularly symmetrical water cylinders, the degrees of hydrocarbon chain splaying and polar group compression are different for molecules aligned in different directions around the water cylinder. (c) A pivotal position exists along the length of the phospholipid molecule where little area change occurs as the monolayer is bent to increasing curvatures. (d) By defining R0 at the pivotal position, we find that measured energies are well fit by a quadratic bending energy, K0/2 (1/R-1/R0); the fit yields bilayer bending moduli of Kc = (1.2-1.7) .times. 10-12 ergs, in good agreement with measurements from bilayer mechanics. (e) For lipid mixtures, enforced deviation of the HII monolayer from R0 is sufficiently powerful to cause demixing of the phospholipids in a way suggesting that the DOPE/DOPC ratio self-adjusts so that its R0 matches the amount of td or water available, i.e., that curvature energy is minimized.