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RESEARCH PRODUCT

Adsorption of proteins on porous and non-porous poly(ethyleneimine) and tentacle-type anion exchangers

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Abstract Adsorption isotherms of proteins [bovine serum albumin (BSA), soybean trypsin inhibitor and alcohol dehydrogenase] on anion exchangers were measured by on-line and off-line methods. The poly(ethyleneimine) (PEI) type and the tentacle-type materials exhibited principally different modes of adsorption. On thin layers of PEI, bonded to non-porous silica, BSA adsorption data corresponded to a monolayer of molecules, with 80% adsorbed side-on, with a high affinity constant for binding, and 20% adsorbed more weakly. With porous material, the amount of BSA bound per unit surface with high affinity was smaller. With tentacle-type anion exchangers, adsorption exceeded a monolayer by far, and data corresponded to a Hill-type isotherm. The Hill coefficients, which were smaller than 1, indicated an approximately Gaussian affinity distribution of the binding sites for the protein. As a consequence, adsorption capacities at elevated ion strength decreased drastically, while the affinity distribution became narrower. Adsorption capacities and binding constants increased with temperature, while Hill coefficients remained unchanged.