Leckband D E, Helm C A, Israelachvili J
Department of Chemical and Nuclear Engineering, University of California, Santa Barbara 93106.
Biochemistry. 1993 Feb 2;32(4):1127-40. doi: 10.1021/bi00055a019.
The interaction forces and fusion mechanisms of mixed zwitterionic-anionic phospholipid bilayers were measured with the surface forces apparatus. The bilayers were 3:1 mixtures of either dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol (DMPC/DMPG) or dilauroylphosphatidylcholine and dilauroylphosphatidylglycerol (DLPC/DLPG), and experiments were carried out in NaCl solutions with and without CaCl2. In NaCl solutions, the forces between either mixed bilayer system were consistent with the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory of repulsive electrostatic and attractive van der Waals forces, and fusion did not occur. At high pH (> 6) and in high (20 mM) NaCl concentrations, a short-range hydration force extending about 13 A was evident, indicative of Na+ binding to the surfaces. In the presence of this large hydration repulsion, the interbilayer adhesion was abolished. When CaCl2 was added to the bathing solutions in the presence or absence of NaCl, the bilayers phase separate into small domains, coinciding with the occurrence of a large, long-range attractive force. Fusion occurred readily between the more fluid domains. The phase separations and fusion events could be directly visualized by observing the shapes of the optical fringes used to measure the surface separation and the change in surface profiles with time. The ease of fusion between mixed bilayers in the presence of calcium correlated closely with the strength of the long-range attractive force. This force is attributed to the additional hydrophobic force between domains or domain boundaries due to the exposure of excess hydrophobic groups resulting from the Ca(2+)-induced condensation of the PG- headgroups.(ABSTRACT TRUNCATED AT 250 WORDS)
使用表面力仪测量了两性离子 - 阴离子混合磷脂双层的相互作用力和融合机制。双层是二肉豆蔻酰磷脂酰胆碱和二肉豆蔻酰磷脂酰甘油（DMPC/DMPG）或二月桂酰磷脂酰胆碱和二月桂酰磷脂酰甘油（DLPC/DLPG）的3:1混合物，实验在有和没有CaCl2的NaCl溶液中进行。在NaCl溶液中，两种混合双层系统之间的力与描述排斥性静电力和吸引性范德华力的DLVO（Derjaguin - Landau - Verwey - Overbeek）理论一致，且未发生融合。在高pH（> 6）和高（20 mM）NaCl浓度下，明显存在约13 Å的短程水化力，表明Na +与表面结合。在这种大水化排斥力存在的情况下，双层间的粘附被消除。当在有或没有NaCl的情况下向浴液中加入CaCl2时，双层会相分离成小区域，同时出现大的、长程吸引力。在流动性更强的区域之间很容易发生融合。通过观察用于测量表面间距的光学条纹形状以及表面轮廓随时间的变化，可以直接观察到相分离和融合事件。在钙存在的情况下，混合双层之间融合的难易程度与长程吸引力的强度密切相关。这种力归因于由于Ca(2 +)诱导的PG头基缩合导致过量疏水基团暴露而在区域或区域边界之间产生的额外疏水力。（摘要截断于250字）
