METAL-AFFINITY PARTITIONING OF PHOSPHOPROTEINS IN PEG DEXTRAN 2-PHASE SYSTEMS

Ferric ion (Fe3+) complexed to iminodiacetic acid (IDA)-polyethylene glycol enhances the partitioning of phosphoproteins in PEG/dextran aqueous two-phase systems. The ratio of partition coefficients in the presence and absence of Fe(III)IDA-PEG, K/K(o), is highly sensitive to pH, increasing in the pH range of 3.0 to 5.0 and decreasing rapidly with a further increase in pH. The steep decline in partition coefficients above pH 5 can be explained by inhibitory binding of hydroxyl ions to ferric ion. In metal-affinity partitioning of phosvitin the most highly phosphorylated protein known, K/K(o) >> 1,000 was obtained. This is one of the highest values reported for affinity partitioning.