Polyethyleneglycol molecular mass and polydispersivity effect on protein partitioning in aqueous two-phase systems

The partitioning of model proteins (bovine serum albumin, ovalbumin, trypsin and lysozyme) was assayed in aqueous two-phase systems formed by a salt (potassium phosphate, sodium sulfate and ammonium sulfate) and a mixture of two polyethyleneglycols of different molecular mass. The ratio between the PEG masses in the mixtures was changed in order to obtain different polymer average molecular mass. The effect of polymer molecular mass and polydispersivity on the protein partition coefficient was studied. The relationship between the logarithm of the protein partition coefficient and the average molecular mass of the phase-forming polymer was found to depend on the polyethyleneglycol molecular mass, the salt type in the bottom phase and the molecular weight of the partitioned protein. The polymer polydispersivity proved to be a very useful tool to increase the separation between two proteins having similar isoelectrical point.