SEPARATION OF PROTEINS FROM POLYELECTROLYTES BY ULTRAFILTRATION

Polyelectrolyte precipitation, while a potentially effective method for concentration and fractionation of proteins, may require subsequent removal of the polyelectrolyte. We report on a strategy of using ultrafiltration membranes to recover proteins in the permeate and polyelectrolyte in the retentate. Separation of polyacrylic acid (PAA) from proteins was successfully carried out using two different membranes. Proteins as small as lysozyme could be permeated with membrane MWCO of 1 x 10(5), whereas larger proteins, such as bovine serum albumin (BSA), required the use of MWCO = 3 x 10(5). Permeation of proteins was found to be dependent on parameters such as pH and ionic strength, which control protein/polyelectrolyte complexation, and stir rate, which controls concentration polarization. In order to determine the limits of applicability of the strategy, experiments were carried out with different molecular weight PAA both in the presence and absence of protein. In the presence of protein, PAA retention was high due to membrane fouling by the protein. In the absence of protein, PAAs of MW < 4 x 10(6) permeated through both membranes to some extent.