Synthetic polyampholytes for protein partitioning in two-phase aqueous polymer systems

Abstract

The equilibrium phase behavior of aqueous systems composed of poly(vinyl alcohol), a synthetic acrylic random polyampholyte (acrylic acid:dimethylaminoethyl methacrylate:methyl methacrylate = 0.9:1:1) and added salts was investigated as a function of polymer concentration, salt concentration and cation type. The formation of two coexisting polymer solution phases (of relatively low viscosity) was observed within a narrow - less than 2 unit - pH range above the isoelectric point of the polyampholyte. In contrast to the phase behavior observed in the two-phase system containing dextran sulfate and poly(ethylene glycol), an increase in salt concentration caused a decrease in the polyampholyte concentration in the polyampholyte-rich phase and the type of monovalent cation appeared to have no measurable effect on the phase composition. Partition coefficients were measured for two proteins with very different isoelectric points (pI):ovalbumin, pI = 4.7

chymotrypsinogen, pI = 9.5, as a function of polymer concentration, salt concentration and cation type. The protein partitioning appeared to be governed by both electrostatic and non-electrostatic effects. The protein recovery in the polyampholyte-rich phase is facilitated through the isoelectric precipitation of the polymer which can then be recycled.