Effects of Adsorption Conditions on Kinetics of Protein Adsorption and Conformational Changes at Ultrafine Silica Particles

Abstract

Human hemoglobin (HHb, a very soft protein) was adsorbed on ultrafine silica particles. Effects of various adsorption conditions on the kinetics of adsorption and conformational changes in HHb were studied. The conformational changes in HHb upon adsorption were monitored by both circular dichroism and absorbance spectra. The adsorption rates were measured using an aqueous two-phase system to very quickly separate the ultrafine silica particles. The rate of conformational changes upon adsorption was significantly affected by pH, ionic strength, and temperature. At high temperature, large conformational changes in HHb were accomplished soon after attachment to the surfaces. On the other hand, at low temperature and/or high ionic strength, the extent of conformational changes accompanying attachment to the surfaces was small, and slow conformational changes occurred after adsorption. Moreover, the rate of conformational changes upon adsorption decreased with increasing adsorption. Renaturation of HHb during desorption was also measured and found to be accomplished within a short time. The percentage of desorbed HHb decreased with increasing adsorption time, because the extent of conformational changes in adsorbed HHb increased. Based on these results, the general tendency of the kinetics of conformational changes in proteins upon adsorption on the solid surfaces are discussed.