MEMBRANE SURFACE PRESSURE--MEASUREMENT AND SIGNIFICANCE

在空气-水界面上的脂质单层 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 自从Gorter和Grendel提出这个问题60年以来， 在他们的论文中提出了双层作为结构基础， 生物膜。 这种压力的估计，这里称为 同形压力范围为低于30 - 50达因/厘米，a 双层表面能的差异超过4千卡/摩尔。 的 如果问题的答案很重要，因为可以使用单层 作为双分子层的模型，也就是天然膜。 当适当 通过检查，它们可以提供难以获得的信息 否则，特别是重要的物理特性， 在蛋白质渗透和疏水的能量学中， 分子以及双层的基本性质，能量 水的界面。 此外，单分子层是 对于许多膜重建方法来说， 这将有助于更好地理解 在双层和单层之间。 本文的目标是：（一） 建立了常见脂质及其 混合物，（二）探索这样的一些性质，和（三） 利用单分子层的性质来理解双层 具有重要生理相关性的特征。 的 目标I的方法是改变表面压力， 单层和双层对应于相变 温度、二维扩散系数和分配 疏水探针的系数。 通过比较这个压力 在双层囊泡的平衡表面压力下， 将获得穿过双层的相互作用能量。 这 能量预计是小的，在这种情况下， 膜的平衡压力（一个非常简单的过程）将 提供同构压力的良好估计。 实现目标 II、基本物理性质（每分子面积， 压缩性、表面势和宏观粘度），或 同构单层将建立使用标准表面 化学技术 实现目标三的办法是测试一个 关于双层膜基本性质的预测，即， 外来分子渗透膜的程度（这里， 脂肪酸和毒素）随着平衡表面的增加而增加 渗透的压力接近表面的压力， 膜（测量为同构单层压力）， 此外，渗透率随着增加而增加， 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酸的平衡表面压力 酸和后者的大温度系数允许 方便测试渗透剂表面压力的影响。 蜂毒肽将用于评估渗透依赖性， 目标膜的表面压力。 磷脂转移 将使用小泡进行测量，因为它们的表面 压力随半径减小，提供了一个方便的系统 研究自渗透，其中二维混合是 必然是理想的。 最后，环境影响的一个方面 表面压力，渗透压，将被检查。

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.