Separation of binary protein mixtures by ultrafiltration

Ultrafiltration of aqueous solutions of mixtures of bovine serum albumin(BSA) and egg white lysozyme was conducted using membranes which were almost completely retentive for BSA, but permeable for lysozyme, in order to investigate the factors influencing the filtration rate and the lysozyme rejection. The experimental data obtained in this study clearly demonstrate that the electrostatic interactions between dissimilar molecules may control the filtration rate and solute rejection in ultrafiltration of binary protein mixtures to a significant degree. It is also shown that increasing the shear stress acting on the membrane causes an increase in the lysozyme rejection, resulting in a reduced fractionation efficiency, and that ultrasonic irradiation is quite effective for fractionation of binary protein mixtures. Furthermore, the properties of the filter cake formed on the retentive membranes in downward dead-end ultrafiltration of binary protein mixtures have been studied in a batchwise filter which has a sudden reduction in its filtration area. In the pH range where both proteins are electropositive, the filter cake becomes loose and wet, thus reducing the flow resistance, while the cake becomes compact and dry in the pH range where the two proteins have opposite electrical charges.