PROTEIN PARTITIONING IN 2-PHASE AQUEOUS POLYMER SYSTEMS .5. DECOUPLING OF THE EFFECTS OF PROTEIN-CONCENTRATION, SALT TYPE, AND POLYMER MOLECULAR-WEIGHT

Measurements of the partitioning behavior of ovalbumin in poly(ethylene oxide) (PEO)-dextran aqueous two-phase system reveal that experimental conditions can be found at which the effects of protein concentration, salt type, and PEO molecular weight can be decoupled. Specifically, the change in the logarithm of the ovalbumin partition coefficient, DELTA(ln K(p)) (where K(p) is the ratio of the protein concentrations in the top PEO-rich phase and the bottom dextran-rich phase), that accompanies a change in PEO molecular weight over the range 5000 to 35 000 Da was measured to be independent of the ovalbumin concentration and the type of salt (NaCl and Na2SO4) present in the system. This observation is used to simplify a general thermodynamic framework that serves as the basis for molecular-level descriptions of protein partitioning in two-phase aqueous polymer systems.