Abstract

Two different series of hydrophobically modified proteins were partitioned in a number of aqueous two-phase systems (ATPS) to investigate the effect of hydrophobicity as a single property on partitioning. The modified proteins were derived from ?-lactoglobulin and bovine serum albumin (BSA). Measurement of the surface hydrophobicity of the proteins is important; hydrophobic interaction chromatography (HIC) was used for this purpose. The resolution of the systems (R) in terms of protein surface hydrophobicity and the intrinsic hydrophobicity (log P0) of the systems was established. The effect of the addition of NaCl to PEG/phosphate and PEG/dextran systems was analyzed in terms of the hydrophobicity difference between the phases and their ability to promote hydrophobic interactions between the protein surface and the PEG molecules. The values for R and log P0 differed somewhat depending on which group of modified proteins was used for partitioning. The addition of NaCl to PEG/phosphate systems promoted an increase in the values of R, showing an important effect on the resolution of the systems for protein surface hydrophobicity (twice as high when compared with systems without NaCl). For PEG/dextran systems, the addition of 9% NaCl (w/w) promoted an improvement in the resolution toward surface hydrophobicity with an increase of 60% on the value of R. The effect of hydrophobicity was investigated as a single property on partitioning by partitioning two different series of hydrophobically modified proteins to several aqueous two-phase systems (ATPS). The surface hydrophobicity of the proteins was measured using hydrophobic interaction chromatography (HIC). Following this, the resolution of the systems (R) in terms of protein surface hydrophobicity and the intrinsic hydrophobicity (log Po) of the systems was established. Finally, the effect of the addition of NaCl to PEG/phosphate and PEG/dextran systems was analyzed in terms of the hydrophobicity difference between the protein surface and the PEG molecules.