盐离子对蛋白质带电特性的影响

本文应用分子理论，研究盐离子对蛋白质带电特性的影响，理论模型考虑蛋白质与阴离子的结合作用。研究发现，由于蛋白质与阴离子的结合，距离蛋白质表面附近处的阴离子被吸附在了蛋白质表面，在距离蛋白质表面附近区域，阴离子分布较少。通过计算体系中的静电势，我们发现，在距离蛋白质表面附近，静电势呈现了较大的负值，带正电荷的阳离子感受到静电吸引，会出现在距离蛋白质表面附近的区域，这会使得在距离蛋白质表面附近的区域，阳离子数目增多。这样，在不同阴离子浓度、以及阴离子与蛋白质不同结合能条件下，阴离子会在不同程度上影响蛋白质的带电特性、影响体系中的静电特性。通过考察不同结合能条件下，蛋白质表面电荷面密度随阴离子浓度的变化关系还发现，较大的结合能会使得阴离子与蛋白质结合增快，蛋白质表面会呈现从正电荷态向负电荷态的转变。理论结果符合实验观测，由此表明，盐离子与蛋白质的结合导致蛋白质表面带电特性的改变，是盐离子影响蛋白质带电特性的本质。

Effect of salt ions on the charging properties of proteins

Using a molecular theory, we investigate the effect of salt ions on the charging properties of proteins. Our model takes bonding interaction between protein and anions. We found, because of the bonding of protein and anion, the anion near the protein surface is adsorbed on the protein surface, and the anion distribution is less in the area near the protein surface. We calculated electrostatic potential of the system, and found the electrostatic potential presented a negative value. Cations can be attracted by electrostatic attractions, which appear in the area near the surface of the protein, and increase the number of cations in the area near the protein. In this way, under different conditions of anion concentration and different binding energy between anion and protein, the anion will affect the charged properties of the protein and the electrostatic properties in the system to varying degrees. By investigation on the relationship between the surface charge density of a protein and the anion concentration under different binding energy conditions, it can also be found that a larger binding energy between anion and protein will make the anion and protein bind faster, and the charged surface density of the protein will present a transition from a positively charged state to negative charge state. Our theoretical results agree with experimental observations, which demonstrate the bonding between salt ions and proteins leads to changes in the charge of proteins, and are the essential characteristics of salt ions that affect the charge properties of proteins.