kinetics of the adsorption of proteins on various surfaces Human hemoglobin (HHb, a very soft protein) was adsorbed have been studied by many researchers using various methon ultrafine silica particles. Effects of various adsorption condiods such as ellipsometry (5-7), Fourier transform infrared tions on the kinetics of adsorption and conformational changes in spectroscopy (FTIR) (8-12), radiolabeling techniques (13, HHb were studied. The conformational changes in HHb upon 14), reflectometry (15-17), and total internal reflection adsorption were monitored by both circular dichroism and abfluorescence (TIRF) (18,. Although the rates of adsorpsorbance spectra. The adsorption rates were measured using an tion of proteins on the surfaces are rather well illustrated, aqueous two-phase system to very quickly separate the ultrafine information on the conformational changes upon adsorption silica particles. The rate of conformational changes upon adsorpon the surfaces is limited.
tion was significantly affected by pH, ionic strength, and temperature. At high temperature, large conformational changes in HHb
In this study, the kinetics of the adsorption of proteins were accomplished soon after attachment to the surfaces. On the and their conformational changes upon adsorption on the other hand, at low temperature and/or high ionic strength, the ultrafine silica particles (average diameter of 15 nm) have extent of conformational changes accompanying attachment to been studied in detail using human hemoglobin (HHb) as the surfaces was small, and slow conformational changes occurred the model protein (molecular weight 64,550, isoelectric after adsorption. Moreover, the rate of conformational changes point 6.8-7.0). HHb has been reported to have a very high upon adsorption decreased with increasing adsorption. Renatuadiabatic compressibility, 10.9 (10 12 b V s), and is thought to ration of HHb during desorption was also measured and found to be a very soft protein (20). Utilization of ultrafine silica be accomplished within a short time. The percentage of desorbed particles is effective in studying the conformational state HHb decreased with increasing adsorption time, because the extent of proteins on the solid surfaces (21-25). Since the lightof conformational changes in adsorbed HHb increased. Based on scattering intensity of ultrafine silica particles is very low, these results, the general tendency of the kinetics of conformational changes in proteins upon adsorption on the solid surfaces the conformation of proteins adsorbed on the particles can are discussed. α§ 1998 Academic Press be evaluated by various spectrophotometric methods. For