Metal Affinity Partitioning of Phosphoproteins in Aqueous Two-Phase Systems

Metal affinity partitioning has been developed to selectively increase the partition coefficients of metal-binding proteins in aqueous two-phase systems (1). Addition of a small amount of Cu(II)IDA-PEG (Cu(II)-iminodiacetic acid-derivatized polyethyleneglycol) to a two-phase system enhances the partitioning of proteins which contain surface-accessible histidines, due to the metal-coordinating ability of histidine. This technique has also been used as a tool to measure stability constants for the metal-protein complexes formed between metal-binding sites and Cu(II) chelated by IDA-PEG (2).