Adsorption dynamics of IgG and its F(ab')(2) and Fc fragments studied by reflectometry

The adsorption of two monoclonal IgG's and their corresponding F(ab')(2) and Fc fragments is followed in real time using reflectometry. The proteins are adsorbed on hydrophilic silica and hydrophobic methylated surfaces, The adsorption experiments are performed at different values for pH and ionic strength, Altogether, these variations enable a systematic study of electrostatic and hydrophobic interactions, The adsorption of IgG and F(ab')(2) on hydrophilic silica is retarded when the proteins are electrostatically repelled by the sorbent surface. This effect is stronger for F(ab')(2) than for whole IgG, whereas the adsorption rate of Fc is not significantly affected, As a function of pH, both IgG's show maximum adsorption around their isoelectric points, At higher ionic strengths these maxima are less pronounced because of screening of electrostatic interactions, After the protein solution is replaced by a buffer solution, desorption is measured, The desorbed amounts indicate that the proteins are more tightly bound to methylated surfaces than to silica, Furthermore, it is observed that, for IgG and Fc adsorbed on silica at low ionic strength, a relatively large fraction desorbs around their isoelectric points whereas this is not the case for F (ab')(2). (C) 1996 Academic Press, Inc.