TEMPERATURE-DEPENDENT PROTEIN PARTITIONING IN 2-PHASE AQUEOUS POLYMER SYSTEMS

The partitioning of ribonuclease A and myoglobin in two different two-phase aqueous polymer systems was investigated experimentally and theoretically. Systems used were poly(ethylene oxide)/dextran/water and Ucon/dextran/water [Ucon being a random poly(ethylene oxide)-poly(propylene oxide) copolymer]. The experiments involved the determination of the temperature and polymer concentration dependence on the partitioning. The theoretical results were obtained through a self-consistent mean-field lattice theory for multicomponent mixtures of copolymers with internal states in heterogeneous systems. Comparisons between theoretical and experimental findings show a qualitative agreement regarding the increased preference for the dextran-rich phase at increased polymer concentrations and the different temperature response displayed by the two systems. Furthermore, details about the temperature response, obtained from the model calculations, are discussed. The overall protein-polymer interaction was found to be repulsive and it is dominated by an entropic repulsion due to the restriction of possible polymer conformations for polymers close to the protein surface. The energetic contribution to the overall interaction is smaller in magnitude. It was repulsive for poly(ethylene oxide) and Ucon, whereas it was attractive for dextran for both proteins.