Chatelier R C, Minton A P
Division of Chemicals and Polymers, CSIRO, Clayton, Victoria, Australia.
Biophys J. 1996 Nov;71(5):2367-74. doi: 10.1016/S0006-3495(96)79430-4.
Equilibrium statistical-thermodynamic models are presented for the surface adsorption of proteins modeled as regular convex hard particles. The adsorbed phase is treated as a two-dimensional fluid, and the chemical potential of adsorbed protein is obtained from scaled particle theory. Adsorption isotherms are calculated for nonassociating and self-associating adsorbing proteins. Area exclusion broadens adsorption isotherms relative to the Langmuir isotherm (negative cooperativity), whereas self-association steepens them (positive cooperativity). The calculated isotherm for adsorption of hard spheres using scaled particle theory for hard discs agrees well with that calculated from the hard disc virial expansion. As the cross section of the adsorbing protein in the plane of the surface becomes less discoidal, the apparent negative cooperativity manifested in the isotherm becomes more pronounced. The model is extended to the case of simultaneous adsorption of a tracer protein at low saturation and a competitor protein with a different size and/or shape at arbitrary fractional saturation. Area exclusion by competitor for tracer (and vice versa) is shown to substantially enhance the displacement of tracer by competitor and to qualitatively invalidate the standard interpretation of ligand competition experiments, according to which the fractional displacement of tracer by competitor is equal to the fractional saturation by competitor.
针对被建模为规则凸硬颗粒的蛋白质表面吸附，提出了平衡统计热力学模型。吸附相被视为二维流体，吸附蛋白质的化学势由定标粒子理论获得。计算了非缔合和自缔合吸附蛋白质的吸附等温线。与朗缪尔等温线相比，面积排斥使吸附等温线变宽（负协同性），而自缔合使其变陡（正协同性）。使用硬圆盘的定标粒子理论计算的硬球吸附等温线与由硬圆盘维里展开计算的结果吻合良好。随着吸附蛋白质在表面平面内的横截面变得不那么呈盘状，等温线中表现出的明显负协同性变得更加显著。该模型扩展到了低饱和度下示踪蛋白与任意分数饱和度下不同大小和/或形状的竞争蛋白同时吸附的情况。结果表明，竞争蛋白对示踪蛋白的面积排斥（反之亦然）会显著增强竞争蛋白对示踪蛋白的置换作用，并使配体竞争实验的标准解释在定性上失效，根据该标准解释，竞争蛋白对示踪蛋白 的分数置换等于竞争蛋白的分数饱和度。
