Metal Affinity Protein Partitioning

The partitioning in aqueous two-phase systems (ATPS) has become an established and well-known method for the separation and purification of biological materials (1 –1 ). In order to increase the selectivity and effectiveness of the separation, a ligand that partitions favorably into one of the phases and with affinity for the material of interest is introduced into the system. Thus, once binding occurs, the desired material preferentially distributes into the polymer-ligand rich phase. In general, the affinity ligand is attached covalently to one of the phase forming polymers, which ensures its primary distribution to one phase of the system. In affinity partitioning, ligands attached to poly(ethylene glycol) (PEG) have been widely described and used extensively in the separation and purification of proteins and cells, derivatives include PEG-linked dyes (4 ; Chapter 30), PEG-linked antibodies (5 ) and PEG-linked long-chained fatty acids (6 ) Chapter 29 6 Chapter 29 ). Similar derivatives for dextran (Dx) and procedures to prepare new affinity ligands are described by Harris (7 ) and Harris and Yalpani (8 ).