Salt partition protein recovery

Recovery of Proteins from Polyethylene Glycol-Water Solution by Salt Partition... 

PEG-water solution, 99f protein recovery by salt partition, 107... 

Miranda and Berglund [79] used a food grade polymer, (hydroxypropyl)methyl cellulose (HPMC), and ammonium sulfate as additives for the recovery of recombinant a-amylase by flotation. The enzyme was removed from the liquid phase by partition to a salted-out HPMC phase and the enzyme-containing polymer floes were recovered by flotation. This system behaved in a manner similar to the flotation of mineral systems. The problem with this technique is the cost of the polymer and the separation of the enzyme from the polymer phase. Both of them complicate the process and increase the separation cost In general, for protein recovery and separation, especially in the pharmaceutical industry, it is not proper to add chemicals to the feed, because they have to be removed from the product completely and this separation causes problems and additive costs. 

A significant amount of work has demonstrated the feasibility and the interest of reversed micelles for the separation of proteins and for the enhancement or inhibition of specific reactions. The number of micellar systems presently available and studied in the presence of proteins is still limited. An effort should be made to increase the number of surfactants used as well as the set of proteins assayed and to characterize the molecular mechanism of solubilization and the microstructure of the laden organic phases in various systems, since they determine the efficiency and selectivity of the separation and are essential to understand the phenomena of bio-activity loss or preservation. As the features of extraction depend on many parameters, particular attention should be paid to controlling all of them in each phase. Simplified thermodynamic models begin to be developed for the representation of partition of simple ions and proteins between aqueous and micellar phases. Relevant experiments and more complete data sets on distribution of salts, cosurfactants, should promote further developments in modelling in relation with current investigations on electrolytes, polymers and proteins. This work could be connected with distribution studies achieved in related areas as microemulsions for oil recovery or supercritical extraction (74). In addition, the contribution of physico-chemical experiments should be taken into account to evaluate the size and structure of the micelles. 

Liquid-liquid extraction using water-soluble polymer solutions provides a mild, nondenaturing extraction system for proteins [1,7]. The most familiar example is partition between a relatively hydrophilic dextran phase and a relatively hydrophobic PEG phase. The selectivity of the two phases can be modulated by addition of salts very high selectivity can be achieved by binding an affinity ligand to a fraction of the PEG polymers. In the case of affinity liquid-liquid extraction, recovery of protein requires modification of the phase to dissociate the bound protein from the polymer, e.g., by a pH change. 

Aqueous two-phase systems have been used as a fast and effective process for separation of biomolecules (Gupta et al, 1999). The two-phase polymer systems are commonly formed by using two incompatible polymer/poly-mer or polymer/salt systems. Poly(ethylene) glycol-dextran systems are commonly used in two-phase separation. Partitioning is a complex process and depends on the surface properties of the proteins. Depending on its hydrophilic/hydrophobic properties the target product concentrates in one of the phases, while the impurities remain in another phase and can be easily removed. The recovery of the protein from the phase-forming polymer is the main bottleneck of the purification process. 

---