COMPUTATION OF THE ELECTROPHORETIC MOBILITY OF PROTEINS

A scheme is presented for computing the electrophoretic mobility of pr oteins in free solution, accounting for the details of the protein sha pe and charge distribution. The method of Teubner is implemented using a boundary integral formulation within which the velocity distributio n, the equilibrium electrical potential around the molecule, and the p otential distribution due to the applied field are solved for numerica lly using the boundary element method. Good agreement of the numerical result is obtained for spheres with the corresponding semi-analytical specialization of Henry's analysis. For protein systems, the method i s applied to lysozyme and ribonuclease A. In both cases, the predicted mobility tensors are fairly isotropic, with the resulting scalar mobi lities being significantly smaller than for spheres of equal volume an d net charge. Comparisons with previously published experimental resul ts for ribonuclease show agreement to be excellent in the presence of a net charge, but poorer at the point of zero charge. The approach may be useful for evaluating approximate methods for estimating protein e lectrophoretic mobilities and for using electrophoretic measurements t o obtain insight into charge distributions on proteins.