EFFECTS OF IONS ON PARTITIONING OF SERUM-ALBUMIN AND LYSOZYME IN AQUEOUS 2-PHASE SYSTEMS CONTAINING ETHYLENE-OXIDE PROPYLENE-OXIDE COPOLYMERS

Aqueous two-phase systems composed of ethylene oxide/propylene oxide r andom co-polymers, EO30/PO70 or Ucon (EO50/PO50), in the top phase and dextran T500 in the bottom phase, have been studied. The cloud point diagram for EO30/PO70 in water solution was determined. EO30/PO70 has a cloud point of 32 degrees C at a concentration of 10% (w/w). The pha se diagram for the system EO30/PO70-dextran T500-water was determined. Salt effects have been studied on the partitioning of two model prote ins, bovine serum albumin and hen egg white lysozyme, in EO30/PO70-dex tran and Ucon-dextran systems. Ions with different hydrophob/city, i.e ., with different position in the Hofmeister or lyotropic series, were investigated with reference to their effect on protein partition. The counterion hydrophobicity was shown to have a strong influence on the partitioning of BSA and lysozyme. Most extreme partitioning was obtai ned with hydrophobic (chaotropic) ions like ClO4- and I-. A comparison of protein partitioning between PEG-dextran and EO30/PO70-dextran has been done. A more extreme protein partitioning was obtained in the EO 30/PO70-dextran containing system. Temperature-induced phase separatio n was studied with EO30/PO70 at 45 degrees C. Both BSA and lysozyme we re completely partitioned to the water phase formed above the cloud po int of EO30/PO70, Model calculations, based on Flory-Huggins theory of polymer solutions, have been done which could reproduce the salt effe ct on the protein partitioning in aqueous-two phase system.