Variation of protein partition coefficients with volume ratio in poly(ethylene glycol)-salt aqueous two-phase systems

Abstract

Partition of total soluble protein from brewery waste in poly(ethylene glycol) (PEG)-phosphate aqueous two-phase systems reveals that the partition coefficient varies with change in volume ratio. This phenomenon has been confirmed by the examination, in more detail, of the behaviour of a pure protein (bovine serum albumin) in systems of widely different volume ratio and tie line length. The results invite interpretation in terms of salting out of protein from the lower phase. The behaviour of a number of pure proteins in hydrophobic interaction chromatography and in PEG salt aqueous two-phase partition has been compared and the results support this interpretation. This is judged to provide a useful rationalisation of three important strategies for the large-scale downstream processing of proteins, namely, precipitation, PEG salt partitioning and hydrophobic adsorption. In addition hydrophobic interaction chromatography may prove to be of benefit in “method scouting” for the development of partitioning strategies in protein purification.