Purification of human fibroblast interferon by extraction in aqueous two-phase systems

Liquid-liquid extraction offers a new method for the concentration and purification of human fibroblast interferon (IFN-beta). Different derivatives of polyethylene glycol (PEG)--liquid ion exchangers or affinity ligands--can be effectively used for the extraction of IFN-beta in combination with Dextran-T 500 or orthophosphate. Important parameters for the partition of IFN-beta have been investigated, e.g., the influence of the concentrations of the phase-forming components, the addition of salts, the volume ratio of the top and bottom phases, and the content of crude IFN-beta. Systems containing polyethylene glycol-phosphate ester/orthophosphate/sodium chloride (1/19.5/2.9% w/w at pH 6.9 or 2/19/7.5% w/w at pH 5-5.9, respectively) resulted in up to 350-fold purified IFN-beta in the top phases with a yield of 74-100% and a specific activity of 3-7 X 10(6) units/mg. The efficiency of extraction in the aqueous phase system is a consequence of an extremely limited solubility of IFN-beta in the bottom phase. One of the advantages of the new method is that it is independent of the process volume and can be performed easily and quickly.