DIRECT MEASUREMENT OF FORCES BETWEEN MEMBRANES OR MACROMOLECULES

这项工作的主题是发展一门有用的、准确的力科学 来组织生物分子。为此，我们集中力量 测量蛋白质、DNA双螺旋和多糖之间的作用力。 直接测力的渗透应力法正在取胜 在世界各地广泛使用。我们的LSB主页包含一个~Living 渗透压力数据和校准曲线手册。记录显示 我们的主页有时会被访问一次 几分钟。 关于DNA作用力的最新研究将渗透胁迫与SAXS和 偏振显微镜。同步辐射和普通x的使用 射线源显示了几种不同形式的分子堆积， 包括具有极大运动自由度的胆固相 (低渗透压下的透析实验扩大了 以前的力测量显示了一种新的涨落增强力 政权)。这种运动增强的显著特征是 将直接力量的射程扩大到原来的四倍。这些观察到的是 与最复杂的液晶物理理论联系在一起 程序集以及直接的问题是DNA如何适应 病毒衣壳等小空间的限制。 粘结剂释放水量的定量测量 不同蛋白质到DNA在脱水过程中表现出质的差异 蛋白质/DNA的关联是特异性的，而不是非特异性的。的确有 分子水合作用的这些变化与 测量到的大分子之间强大的水合力 联系。 我们终于在一个重大的理论问题上取得了明显的进展， 令人讨厌的“蒸汽压悖论”，在这种情况下，膜被吸收 来自蒸汽的水比来自相同化学物质的液体溶液的水少 像水一样有潜力。根据我们的公式，一种表面抑制 分子运动会在很远的地方对介质施加抑制(甚至 细胞维度)，并将停止分子扩张。在使用后的几周内 最初的配方，向另一家实验室建议的实验表明 一种预测到的表面扰动。其他实验室现在正在展示 我们已经确定的现象的一般性。其后果是 这项工作就是我们必须问双层的溶液性质是否 膜，或半柔性~分子，如DNA，在 微米宽的范围，就像它们在厘米大小的容器中一样 他们通常是被研究的。

The theme of this work is to develop a useful, accurate science of forces that organize biomolecules. To this end we have concentrated our efforts t measure forces between proteins, DNA double helices, and polysaccharides. The Osmotic Stress method for direct force measurements is winning widespread use around the world. Our LSB home page contains a ~living handbook~ of osmotic stress data and calibration curves. Records indicate that our home page is sometimes accessed as often as once every couple of minutes. The latest work on DNA forces combines osmotic stress with SAXS and polarization microscopy. Use of synchrotron radiation as well as ordinary x ray sources has shown several different forms of molecular packing, including a cholesteric phase characterized by great motional freedom (dialysis experiments at low osmotic pressures extended the range of previous force measurements demonstrating a new fluctuation enhanced force regime). The remarkable feature of this motional enhancement is a quadrupling of the range of direct forces. These observations are being connected with the most sophisticated physical theories of liquid-crystal assembly as well as with immediate questions how DNA fits within the confines of small spaces such as viral capsids. Quantitative measurement of the amount of water released upon the binding o various proteins to DNA shows qualitative differences in dehydration when the protein/DNA association is specific rather than non-specific. There is an apparent connection between these changes in molecular hydration and the powerful "hydration forces" measured between large molecules brought into contact. We have finally enjoyed clear progress on a major theoretical question, the annoying, "vapor pressure paradox," wherein membranes are known to imbibe less water from a vapor than from a liquid solution of the same chemical potential as water. According to our formulation, a surface that suppresse molecular motion will exert its repression very far into a medium (even cellular dimensions) and will stop molecular expansion. Within weeks of ou initial formulation, experiments suggested to another laboratory showed the kind of surface perturbation that was predicted. Other labs are now showin the generality of the phenomenon we have identified. The consequence of this work is that we must ask whether the solution properties of bilayer membranes, or ~semi-flexible~ molecules such as DNA, are the same within th micron-wide confines as they are in the centimeter-size vessels in which they are normally studied.