Abstract: Sulfonate group is the most common ligand used for purifying lactoferrin. The isotherm adsorption curves of lactoferrin on three adsorbents with sulfonic ligand at different pHs and salt concentrations showed that adsorption capacity decreased with the increase of pH or salt concentration. Further molecular simulation was performed to compare the electrostatic potential of lactoferrin under different conditions. It could be presumed that the mechanism of pH effect was the change of protonation of amino acid residues on the surface of protein and the change of electrostatic potential consequently, while the mechanism of salt effect could be the shield of electrostatic interaction between protein and ligand with no impact on electrostatic potential distribution obviously. Finally, the binding energy between protein and ligand under different conditions was calculated to quantify adsorption capacity and characterize the effects of pH and salt concentration.

Key words: lactoferrin, adsorption isotherms, pH, salt concentration, molecular simulation, electrostatic potential, binding energy

摘要： 磺酸基团是用来分离乳铁蛋白普遍被认可的配基，因此含有磺酸基团的层析剂是被用得最广泛的分离介质。通过对三种接有磺酸基团的层析介质，在不同pH和盐浓度时的静态吸附研究，得到了吸附的基本规律：随着pH或盐浓度的增大，吸附容量降低。利用分子模拟技术，比较了乳铁蛋白分子表面电势在不同条件时的变化，推测pH影响吸附的机理在于改变了蛋白表面氨基酸残基的质子化状态和分子表面电势，而盐浓度主要是屏蔽了蛋白和配基之间的相互作用，改变蛋白分子表面整体电势强弱，对电势分布没有明显影响。通过计算蛋白和配基之间的结合能，量化不同条件下的吸附能力，表征pH和盐浓度的影响。

关键词: 乳铁蛋白, 静态吸附, pH, 盐浓度, 分子模拟, 表面电势, 结合能