UPWARD DEAD-END ULTRAFILTRATION OF BINARY PROTEIN MIXTURES

Upward dead-end ultrafiltration of aqueous solutions of mixtures of bo vine serum albumin (BSA) and egg white lysozyme was conducted using me mbranes which are almost completely retentive for BSA but permeable fo r lysozyme. The dependence of lysozyme rejection and the filtration fl ux rate on pH and the addition of salts has been investigated. The exp erimental data obtained in this study clearly demonstrate that the ele ctrostatic interactions between dissimilar molecules may control the s olute rejection and the filtration rate in upward ultrafiltration of b inary protein mixtures. For instance, the BSA and lysozyme molecules h ave opposite electric charges at pH 7. Consequently, lysozyme rejectio n is large because both molecules within the filter cake pack more tig htly due to heterocoagulation. On the other hand, the BSA and lysozyme molecules have the same electric charge at pH 4. Thus, lysozyme is re jected by the filter cake of the retained BSA molecules due to repulsi ve electrostatic interactions between the positively charged proteins. However, these charge effects weaken in the presence of salts. This s tudy revealed that the solution environment can have profound effects upon solute and solvent transport in the ultrafiltration of binary pro tein mixtures.