MODEL FOR PREDICTING THE PARTITION BEHAVIOR OF PROTEINS IN AQUEOUS 2-PHASE SYSTEMS

The effect of protein hydrophobicity, charge, molecular mass and concentration has been studied in poly(ethylene glycol) (PEG)-phosphate and PEG-dextran aqueous two-phase systems in the presence and absence of NaCl for several model proteins. The surface hydrophobicity of the protein measured by precipitation correlated well with the partition coefficient in PEG-salt systems at high levels of NaCl. The charge of proteins also has an important effect on partition; this is expected to be more pronounced at lower NaCl concentrations. For molecular mass a tendency was found in PEG-dextran systems at low NaCl concentrations. No clear tendency was observed in the PEG-salt systems. The solubility of the protein in the phases also affects its partition behaviour. This behaviour was fitted to a saturation type equation for alpha-amylase in each of the phases of a PEG-phosphate system