Liquid-liquid extraction of a recombinant protein, cytochrome b5, with aqueous two-phase systems of polyethylene glycol and potassium phosphate salts.

The partitioning of cytochrome b5 in aqueous two-phase systems of polyethylene glycol (PEG) and potassium phosphate salts was investigated. Cytochrome b5 partitioning is enhanced with decreasing polymer molecular mass and with increasing tieline length and pH. The effect of cytochrome b5 mutation, by substitution of the glutamic acid at positions 56 and 92 of the polypeptide chain by a lysine, on protein partitioning was also studied. Partitioning of cytochrome b5 mutants shows the same dependence on tieline length and pH, following the order cytochrome b5 > mutant 56 > mutant 92.