Comparison between the thermodynamic features of α1-antitrypsin and human albumin partitioning in aqueous two-phase systems of polyethyleneglycol-dextran Original Research Article

The partitioning features of human serum albumin and α1-antitrypsin in aqueous two-phase systems of dextran and polyethyleneglycol were studied. The effect of factors that affect the electrostatic term of Albertsson equation such as pH, ionic strength, presence of neutral salts as well as those which affect the non-electrostatic term such as polyethyleneglycol mol. wt. and temperature were assayed. At room temperature, the positive entropy and enthalpy changes associated to the partition may be due to a release of part of the structured water in the domain of proteins caused by H-bonds rupture when the proteins are transferred to the upper phase. This behaviour may be explained on the basis of a preferential hydration of the proteins in presence of dextran (bottom phase) and a preferential interaction of polyethyleneglycols with the protein domain (top phase). The electrostatic interactions were similar for both proteins due to the proximity of their isoelectric point and similar dissociation profiles of their prototropic groups.