The effect of protein concentration on electrophoretic mobility

The electrophoretic mobility of haemoglobin was measured in a novel membran e-electrophoresis cell and by electrophoretic light scattering. The effect of protein concentration was investigated at different ionic strengths in t wo different buffer systems. The results indicated that although the effect of the concentration is weak, the mobility did decrease linearly with an i ncrease in volume fraction throughout the range of volume fractions investi gated (phi < 0.06). This dependence is more pronounced at lower kappa a val ues where double-layer interactions between the particles are more signific ant. Protein contribution to the solution ionic strength alone cannot expla in the observed reduction in electrophoretic mobility. The theory of Shugai et al. (Shugai, A. A., Carnie, S. L., Chan, D. Y. C., and Anderson, J. L, J. Colloid Interface Sci. 191, 357 (1997)) was found to be adequate in desc ribing particle interactions. The agreement with Shugai's theory is somewha t surprising considering the polydispersed nature of the samples, uncertain ties in protein size, changes in ionic strength at high protein concentrati ons, and possible membrane-protein interactions not accounted for in the th eory. (C) 2000 Academic Press.