Adsorption of γ‐globulin, a model protein for antibody, on colloidal particles

Abstract

The effect of surface properties on the adsorption of bovine γ‐globulin, a model protein for antibody, was studied. Polystyrene latex (PS), hydrophilic copolymer lattices of styrene/2‐hydroxyethyl methacrylate [P(S/HEMA)], styrene/ methacrylic acid [P(S/MAA)] and methyl methacrylate/ 2‐hydroxyethyl methacrylate [P(MMA/HEMA)], and colloidal silica were used. The adsorption isotherms of γ‐globulin on these colloidal particles were measured as a function of pH and ionic strength. The hydrophilic particles showed low affinities for γ‐globulin at alkaline pH, while PS showed high affinities for γ‐globulin over the whole range of pH and ionic strength. The γ‐globulin adsorption on hydrophilic particles was highly reversible with respect to the pH and ionic strength compared with that on PS. These differences indicate that the dominant driving forces of adsorption are related to the hydrophilicity of particles. The adsorption isotherms of all colloidal particles showed the plateau values, and the order of maximum values of plateau adsorption was P(S/MAA) > PS or P(S/HEMA), silica > P(MMA/HEMA). Thus, they were also affected by the charged groups and the hydrophilicity of the surfaces. On the other hand, the plateau values of all colloidal particles were more or less symmetrical with a maximum at around the isoelectric point of γ‐globulin at an ionic strength of 0.01. This behavior is attributed to the important role of the lateral interaction between the adsorbed molecules at low ionic strength.