DIRECT MEASUREMENT OF FORCES BETWEEN MEMBRANES OF MACROMOLECULES

能够直接测量膜之间或膜之间的力 大分子正在创造一种思考分子的新逻辑 组装和折叠。交互的突出特点是，作为 分子或膜接近接触，接近的重要工作 包括从相对表面去除有组织的水溶剂。 这些“水合力”现在被认为在材料中起着不同的作用。 作为脂双层、DNA双螺旋和硬线状多糖。 到目前为止，只有力或能量与分子之间的表面间隔或 对膜进行了测量。在本年度，“熵”和 释放水的“焓”，作为距离的函数 大分子，已被成功提取。 对多糖之间作用力的系统研究的第一阶段是 也已经完工了。同样，对于这些材料，如核酸和 脂质，人们看到指数级衰减的“水合”力量 分子正在接近接触。 一种声称与“偶极”有关的脂双层作用力理论 ]由脂类极性基团对水的扰动建立的“势” 正在进行脂质界面附近的测试。一种综合渗透胁迫，x射线 衍射谱、核磁共振和离子输运研究表明，这种关联 理论所要求的并不存在。 合成脂质的双层，从别人的工作中想不出来 强大的水合力，现在已经显示出这种力的一个非常强的版本 用我们的直接渗透应激法观察。 最后，片层和非片层之间的转换出奇地简单 脂类堆积，其发生可能与容易重排有关 正在研究分泌和融合过程中的细胞膜脂质。

The ability to measure directly the forces between membranes or between macromolecules is creating a new logic for thinking about molecular assembly and folding. The outstanding feature of interaction is that as molecules or membranes approach contact, the important work of approach involves removal of organized water solvent from the apposing surfaces. These "hydration forces" are now recognized to act in materials as diverse as lipid bilayers, DNA double helices, and stiff linear polysaccharides. Until now, only force or energy vs. surface separation between molecules or membranes has been measured. During the current year, the "entropy" and "enthalpy" of release water, as a function of the distance between macromolecules, has been successfully extracted. The first phase of a systematic study of forces between polysaccharides has also been completed. Again, for these materials as for nucleic acids and lipids, one sees exponentially decaying "hydration" forces between molecules approaching contact. A theory of lipid bilayer forces that claims to relate the "dipole ]potential" set up by the lipid polar groups to the perturbation of water near the lipid interface is being tested. A combined osmotic stress, x-ray diffraction, NMR and ion transport study shows that the correlation demanded by the theory does not exist. Bilayers of synthetic lipids, thought from the work of others not to show strong hydration forces, have now shown a very strong version of this force when observed by our direct, osmotic stress method. Finally, a surprisingly easy transition between lamellar and non-lamellar packing of lipids whose occurrence may be related to easy rearrangement of cell membrane lipids in secretion and fusion is being investigated.