Allison S A, Tran V T
Department of Chemistry, Georgia State University, Atlanta 30303, USA.
Biophys J. 1995 Jun;68(6):2261-70. doi: 10.1016/S0006-3495(95)80408-X.
An algorithm is developed to determine the electrophoretic mobility of a rigid polyion modeled as a low dielectric volume element of arbitrary shape containing an arbitrary charge distribution. The solvent is modeled as a high dielectric continuum with salt distributed according to the linearized Poisson Boltzmann equation. Account is also taken of a Stern layer that separates the molecular surface and the surface of hydrodynamic shear, or Stern surface. Relaxation of the ion atmosphere because of the presence of the external field is ignored. The electrostatic and hydrodynamic problems are both solved by boundary element methods. The procedure is first applied to spherical polyions containing monopolar, dipolar, and quadrupolar charge distributions, and calculated mobilities are found to be in excellent agreement with the theory of Yoon and Kim. It is then applied to lysozyme by using models that account for the detailed shape and charge distribution of the enzyme. For reasonable choices of the molecular and Stern surfaces, calculated and experimental mobilities are found to be in fair agreement with each other. However, if a pH independent Stern layer (or, equivalently, translational diffusion constant, Dt) is assumed, the calculated mobilities exhibit a stronger pH dependence than is observed experimentally. A small increase in Dt with increasing pH could correct this discrepancy.
开发了一种算法，用于确定刚性聚离子的电泳迁移率，该聚离子被建模为具有任意电荷分布的任意形状的低介电体积元素。溶剂被建模为高介电连续介质，盐根据线性化的泊松-玻尔兹曼方程分布。还考虑了一个斯特恩层，它将分子表面与流体动力学剪切表面或斯特恩表面分隔开来。忽略了由于外部场的存在而导致的离子氛的弛豫。静电和流体动力学问题均通过边界元法求解。该程序首先应用于包含单极、偶极和四极电荷分布的球形聚离子，发现计算出的迁移率与Yoon和Kim的理论非常吻合。然后通过使用考虑酶的详细形状和电荷分布的模型将其应用于溶菌酶。对于分子表面和斯特恩表面的合理选择，发现计算出的迁移率与实验迁移率相当吻合。然而，如果假设一个与pH无关的斯特恩层（或者等效地，平移扩散常数Dt），则计算出的迁移率表现出比实验观察到的更强的pH依赖性。随着pH值的增加，Dt的小幅增加可以纠正这种差异。
