New aqueous two-phase systems based on poly(ethylene oxide sulfide) (PEOS) and potassium phosphate for the potential recovery of proteins
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A new aqueous two-phase system (ATPS) based on a degradable polymer called poly(ethylene oxide sulfide) with a molecular weight of 33 000 g mol-1 (identified as PEOS-12) and potassium phosphate was exploited for the potential recovery of proteins. An initial characterisation of the ATPS was achieved by the construction of a phase diagram for the PEOS-12/phosphate system. The protein partitioning behaviour of lysozyme and bovine serum albumin (BSA), selected as single model proteins, and B-phycoerythrin (BPE) produced by Porphytidium cruentum in the new ATPS under increasing tie line length (TLL) conditions at constant phase volume ratio (Vr) and system pH was investigated. Both single proteins partitioned in the new ATPS, initially exhibiting bottom phase preference; however, lysozyme changed phase preference when TLL was increased. Fractionation of a complex model (production of BPE by P. cruentum) using PEOS-12/phosphate ATPS was performed to evaluate the potential protein recovery from fermentation broth or cell homogenate. The proposed new ATPS proved to be suitable for the potential recovery of BPE from crude extract of P. cruentum. In general, a system comprising Vr = 1.0, 18% (w/w) PEOS-12, 8% (w/w) phosphate and 30% (w/w) TLL at pH 7.0 provided conditions to concentrate BPE into the bottom phase (i.e. partitioning behaviour of BPE; In KBPE = -1.8) with a protein recovery of 84%. The findings reported here demonstrate the potential application of the new ATPS for the recovery of proteins from complex biological suspensions. © 2006 Society of Chemical Industry.