Effect of ion binding on protein transport through ultrafiltration membranes

Electrostatic interactions can have a significant impact on protein transmi ssion through semipermeable membranes. Experimental data for the transport of bovine serum albumin (BSA) through a polyethersulfone ultrafiltration me mbrane were obtained in different salt solutions over a range of pH and sal t concentrations. Net BSA charge under the same conditions was evaluated fr om mobility data measured by capillary electrophoresis. The results show th at specific ionic composition, in addition to solution pH and ionic strengt h, can strongly affect the rate of protein transport through semipermeable ultrafiltration membranes. The effects of different ions on BSA sieving are due primarily to differences in ion binding to the protein, which leads to significant differences in the net protein charge at a given pH and ionic strength. This effect could be described in terms of an effective protein r adius, which accounts for the electrostatic exclusion of the charged protei n from the membrane pores. These results provide important insights into th e nature of the electrostatic interactions in membrane systems. (C) 1999 Jo hn Wiley & Sons, Inc. Biotechnol Bioeng 63: 298-307, 1999.