ELECTROPHORETIC MOBILITIES OF PROTEINS AND PROTEIN MIXTURES IN POROUSMEMBRANES

The electrophoresis of bovine serum albumin (BSA) and bovine haemoglob in (BHb) through microfiltration membranes has been investigated using an apparatus consisting of two well-stirred chambers separated by a m icrofiltration membrane, with electrode compartments at each end. The electrophoretic mobilities of the proteins were determined under condi tions of zero concentration driving force and with negligible adsorpti on on to the membranes occurring during an experiment. Using a track-e tched membrane of 9% porosity and 0.2 mu m pore size, the initial mobi lities of both proteins were close to published free-solution values a t the same pH, after correction for the ionic strength of the buffer; this was so because the effect of reduced free area in the membrane wa s compensated by a corresponding increase in the potential gradient. S imilar values were also obtained for BHb with four other microfiltrati on membranes of 70-75% porosity and 0.10 to 0.22 mu m pore size, made from various materials; however BHb mobilities 26% lower were obtained with a membrane of 0.025 mu m pore size. Data were also obtained for mixtures of the two proteins; these indicated, as expected, that inter actions occurred when they were oppositely charged, changing the appar ent mobilities from the free solution values. The single protein data were interpreted using a phenomenological model, which incorporated th e effects of electroosmotic flow resulting From membrane surface charg e, hydrodynamic drag, pressure-driven back-flow and back-diffusion. Th e mixed protein data were modelled using the Maxwell-Stefan relations, with promising results. Copyright (C) 1996 Elsevier Science Ltd.