COMPETITIVE ADSORPTION OF HUMAN SERUM-ALBUMIN AND GAMMA-GLOBULIN FROMA BINARY PROTEIN MIXTURE ONTO HEXADECYLTRICHLOROSILANE COATED GLASS

The kinetics of competitive adsorption of proteins onto hexadecyltrich lorosilane coated glass (HTS-glass) from model solutions containing fl uorescein isothiocyanate (FITC)-labeled human serum albumin (HSA-FITC) and gamma-globulin (HGG-FITC) were studied by total internal reflecti on fluorescence (TIRF) spectroscopy. The processes of displacement of HSA-FITC by HGG are independent of the conformational state of HSA ads orbed onto glass. On HTS-glass, displacement of protein is hindered by the presence of large numbers of CH3-terminated alkyl tails which ind uce conformational (reorientational) changes in HSA-FITC and HGG-FITC adsorbed from simple solutions. In contrast to HSA, adsorption of HGG onto HTS-glass from a simple solution is characterized by the absence of irreversible adsorption in the initial portion of the kinetic curve . Competition between HSA and HGG-FITC induces replacement of end-on a dsorbed HGG-FITC on HTS-glass surface with subsequent desorption of th e HGG-FITC into solution. Upon further increase in the HSA concentrati on in solution the competition of HSA for adsorption sites prevails, w hich leads to a decrease in the amount of adsorbed HGG-FITC and, conse quently, to a decrease in the rate of its displacement.