COMPARATIVE PROTEIN ADSORPTION IN MODEL SYSTEMS

Adsorption of the proteins lysozyme, ribonuclease, and α-lactalbumin was studied. The proteins have similar size and shape, but their isoelectric points and structure stability differ. The adsorbents were hydrophilic silica and hydrophobic polystyrene-coated silica, which are both negatively charged. The adsorption process was monitored by reflectometry, from which the total adsorbed amount could be derived, and by streaming potential measurements, which provided information on the composition of the adsorbed layer. Applying these two techniques yielded conclusive data as to sequential and competitive protein adsorption. On the hydrophilic silica the preference between the proteins in sequential and competitive adsorption is ruled by electrostatics. Sequential adsorption occurs by displacement of the preadsorbed protein. On the hydrophobic surface the preference is influenced by electrostatic interactions to a lesser extent and sequential adsorption is accompanied by only partial desorption of the preadsorbed protein. © 1990.