MEMBRANE SURFACE PRESSURE--MEASUREMENT AND SIGNIFICANCE

在空气-水中有多少脂单分子层的问题 应压缩界面以产生分子堆积 与双层中相同脂质的排列相对应的排列 自戈特和格伦德尔提出这一问题60年来一直没有得到答复 在他们的论文中提出了双层作为结构基础 生物膜。对这种压力的估计，在这里称为 同象压力，范围从30到50dynes/cm，a 双分子层表面能差大于4千卡/摩尔。这个 回答这个问题是否重要，因为可以使用单层 作为双层膜的模型，从而成为天然膜的模型。当适当的时候 经过检查，它们可以提供难以获得的信息 否则，特别是重要的物理属性 在蛋白质浓度和疏水性的能量学中 分子以及双层的一个基本性质，即能量 在水界面上。此外，单层是开始。 对于很多膜重建方法来说，成功的 这将受益于对两国关系的更好理解 在双层和单层之间。这项建议的目的是(一) 建立普通脂质及其同构压力的计算方法 混合物，(Ii)探索这种混合物的一些性质，以及(Iii) 利用单层性质来理解双分子层 具有重要生理相关性的特征。这个 接近目标I将改变表面压力直到 单层和双层对应于相变 温度、二维扩散系数和分配 疏水探头的系数。通过比较这种压力 在双层囊泡的平衡表面压力下， 将获得跨双分子层的相互作用能量。这 能量预计很小，在这种情况下，测量 膜的平衡压力(一个非常简单的过程)将 提供了同构压力的一个很好的估计。实现目标 基本物理性质(每个分子的面积， 可压缩性、表面势和宏观粘度)或 将使用标准表面建立同构单层 化学技术。实现目标三的方法将是测试一个 关于双层的基本性质的预测，即 外来分子对膜的穿透程度(此处， 脂肪酸和毒素)随着平衡表面的增加而增加 侵彻压力接近表面压力。 膜(以同构单层压力测量)和 渗透率随剂量的增加而增加。 膜的可压缩性。两者之间的巨大差异 顺式和反式不饱和脂肪的平衡表面压 酸和后者的大温度系数允许 方便测试渗透表面压力的影响。 蜂毒素将被用来评估渗透率对 靶膜的表面压力。磷脂转移 将使用小泡来测量，因为它们的表面 压力随着半径的减小而减小，提供了一个方便的系统 要研究自渗透，其中二维混合是 当然是理想的。最后，环境影响的一个方面 我们将考察表面压力和渗透压的关系。

The question of how much a lipid monolayer at the air-water interfece should be compressed to yield a molecular packing arrangement corresponding to that of the same lipid in a bilayer has remained unanswered since Gorter and Grendel raised it 60 years ago in their paper proposing the bilayer as the structural basis of biological membranes. Estimates of this pressure, here termed the isomorphic pressure, range from below 30 to 50 dynes/cm, a differnce in bilayer surface energy of over 4 kcal/mole. The answer to the question if important because monolayers can be used as models for bilayers and hence, natural membranes. When properly examined, they can provide information difficult to obtain otherwise, in particular, physical properties that are important in the energetics of the pentration of proteins and hydrophobic molecules as well as a fundamental property of bilayers, the energy of the aqueous interface. In addition, monolayers are the starting point for many membrane reconstitution methods, the success of which will benefit from greater understanding of the relationship between bilayers and monolayers. The goal of tis proposal are (I) to establish the isomorphic pressure for common lipids and their mixtures, (II) to explore some of the properties of such, and (III) make use of monolayer properties to understand come bilayer characteristics that have important physiological relevance. The approach to Goal I will be to vary the surface pressure until monolayer and bilayer correspond with respect to phase transition temperature, 2-dimensional diffusion coefficient and partition coefficient of a hydrophobic probe. By comparing this pressure with the equilibrium surface pressure of bilayer vesicles, the energy of interaction across the bilayer will be obtained. This energy is expected to be small, in which case, measurement of the equilibrium pressure of a membrane (a very simple procedure) will provide a good estimate of the isomorphic pressure. To meet Goal II, the basic physical properties (area per molecule, compressibility, surface potential and macroviscosity) or isomorphic monolayers will be established using standard surface chemical techniques. The approach to Goal III will be to test a prediction about fundamental properties of bilayers, namely that the extent of membrane penetration by a foreign molecule (here, fatty acids and a toxin) increases as the equilibrium surface pressure of the penetration approaches the surface pressure of the membrane (measured as the isomorphic monolayer pressure) and that the rate of penetration increases in addition with increasing compressibility of the membrane. The large difference between the equilibrium surface pressures of cis- and trans-unsaturated fatty acids and the large temperature coefficient of the latter allow convenient testing of the influence of penetrant surface pressure. Melittin will be used to assess dependence of penetration on surface pressure of the target membrane. Phospholipid transfer will be measured using small vesicles, which because their surface pressure decreases with their radius, provide a convenient system to investigate self-penetration, where 2-dimensional mixing is necessarily ideal. Finally, one aspect of environmental effects on surface pressure, that of osmotic pressure, will be examined.