Influence of sodium chloride on hydrophobic adsorption of PEGylated lysozyme



Interaction of macromolecules in aqueous salt-containing solution with a hydrophobic adsorbent is studied by adsorption equilibrium measurements and by independent isothermal titration calorimetry. The macromolecules are native as well as mono-, di-, and tri-PEGylated lysozyme and four pure PEGs. The hydrophobic adsorbent is Toyopearl PPG-600M. The salt is sodium chloride. The sodium chloride concentration in the aqueous 25 mM sodium phosphate buffer is varied from 2000 to 4500 mM at pH 7.0 and 25°C. PEGylation of the lysozyme is carried using 5 and 10 kDa PEG chains. The molar enthalpy of adsorption math formula is calculated from the adsorption equilibrium and the calorimetric data. The results show that the adsorption of the PEGylated lysozyme is caused by both the interaction of the lysozyme and the interaction of the PEG chains with the adsorbent, respectively, but the interaction of the lysozyme is stronger than that of PEG. The comparison of the results of the present study on the influence of sodium chloride with a corresponding study on the influence of ammonium sulfate shows that the adsorption mechanism changes upon the variation of the salt. The knowledge of the adsorption mechanisms supports the systematic development of chromatographic purification steps.