Protein adsorption to poly(ethylenimine)-modified Sepharose FF: III. Comparison between different proteins

Previously, we studied bovine serum albumin (BSA) uptake to poly(ethylenimine) (PEI)-grafted Sepharose resins, and an ionic capacity (IC) range (600–740 mmol/L) for steep increases of both protein capacity (qm) and effective pore diffusion coefficient (De) was found. In this work, seven PEI-grafted Sepharose FF resins at IC range of 270–1030 mmol/L were synthesized to investigate the effect of protein properties on the adsorption and uptake kinetics using BSA and γ-globulin as two model proteins. For BSA, the change trends of qm and De values with IC were well consistent with the previous results. For γ-globulin, the qm values increased slowly till reaching a maximum value at IC = 560 mmol/L and then decreased rapidly at IC > 560 mol/L. The De values nearly kept unchanged at low ICs (IC < 460 mmol/L), and increased steeply at IC > 460 mmol/L till reaching a maximum at 680 mmol/L (De/D0 = 0.48 ± 0.01). After that increase, the De values for γ-globulin dropped quickly at IC > 680 mol/L, which was not observed for BSA. It is interesting to note that in the narrow IC range of 460–680 mmol/L, the De values of γ-globulin increased dramatically for more than four folds. Moreover, it is notable that the IC range where the hopping of De values occurred for γ-globulin was earlier than that for BSA (460 vs. 560 mmol/L). The earlier hopping of γ-globulin uptake rate was attributed to its larger size and less net charge, which facilitated the happenings of the “chain delivery” effect. The quick drops of both qm and De values for γ-globulin at IC > 680 mmol/L were considered due to its large size, which led to the significant decrease of its effective pore volume. The results indicate that both PEI layer and protein size played important roles in protein adsorption to PEI-grafted resins, and further prove the “chain delivery” effect did contributed significantly to the uptake rate hopping in the PEI-grafted resins. This work could also help the design and selection of resins based on protein characteristics and benefit optimization of practical chromatographic processes for therapeutic proteins with PEI-grafted anion exchangers.