ADSORPTION DYNAMICS OF IGG AND ITS F(AB')(2) AND FC FRAGMENTS STUDIEDBY 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 value s for pH and ionic strength, Altogether, these variations enable a sys tematic study of electrostatic and hydrophobic interactions, The adsor ption of IgG and F(ab')(2) on hydrophilic silica is retarded when the proteins are electrostatically repelled by the sorbent surface. This e ffect is stronger for F(ab')(2) than for whole IgG, whereas the adsorp tion rate of Fc is not significantly affected, As a function of pH, bo th IgG's show maximum adsorption around their isoelectric points, At h igher ionic strengths these maxima are less pronounced because of scre ening of electrostatic interactions, After the protein solution is rep laced by a buffer solution, desorption is measured, The desorbed amoun ts indicate that the proteins are more tightly bound to methylated sur faces 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.