Effect of electrodynamic interactions on the translational diffusion of bovine serum albumin at finite concentration

Abstract

Experimental studies of the translational diffusion coefficient, D t, of the globular protein bovine serum albumin at very high ionic strength ( I > 1.0) are reported. These data and literature values of D t at moderate ionic strengths (0.1 < I < 1.0) are compared with the predictions of recent hydrodynamic theory. In the theoretical analysis, the combined effects of long-range repulsive (electrostatic) and attractive (electrodynamic) forces are included. The latter may make significant contributions near the isoelectric pH and at moderate ionic strength. At very high ionic strength, all long-range interactions are essentially completely screened, and the diffusion characteristics at finite concentration are dominated by the hard-sphere core repulsion. The experimental diffusion coefficients for bovine serum albumin (BSA) at pH 7.4 and I = 4.0 appear to be in harmony with literature data for D t measured at the isoelectric pH and I = 0.1, provided an appropriate correction for the electrodynamic interaction is included in the latter.