Microcalorimetric study of the adsorption of native and mono-PEGylated bovine serum albumin on anion-exchangers.

The adsorption of native bovine serum albumin (BSA) and 12 kDa-PEG-BSA on 12 different commercially available strong and weak anion-exchange resins is studied at 25 °C and pH 7. The resins differ in their base matrix material, their functional groups and the type of polymer modification. A combination of equilibrium measurements and microcalorimetric experiments is used to determine the specific enthalpy of adsorption of the proteins. From these data, the entropic contributions to the specific Gibbs energy of adsorption are determined. The results strongly differ for different resins. They also depend on the loadings. The adsorption of BSA on strong (Q) anion-exchangers is exothermic and enthalpy-driven. The adsorption of BSA on weak (DEAE) anion-exchangers is endothermic and entropy-driven. The adsorption of PEG-BSA on strong (Q) anion-exchangers is exothermic or endothermic, depending on the resin, while the adsorption of PEG-BSA on weak (DEAE) anion-exchangers is exothermic for all studied resins. The present study provides a large body of new experimental data that contribute to the understanding of the nature of protein adsorption on ion exchange resins and the influence of the resin properties and polymer modification of the proteins on this process.
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