DIFFERENTIAL SURFACE BINDING OF ALBUMIN, IMMUNOGLOBULIN-G AND FIBRINOGEN

Protein-protein interactions, as well as the nature of the surface, significantly affect the activity of a specific protein towards a defined surface. Indications are that protein-protein associations may affect antibody detectability, but in some cases this is the result of altered antigenic accessibility rather than physical removal of the molecule. The antibody binding patterns are also quite variable over an entire methyl-silanol wettability gradient on silicon, suggesting that the surface itself is affecting protein-protein and protein-protein-surface associations. Ellipsometric studies were carried out on the gradients which were incubated in single, binary and tertiary physiological concentration solutions of human albumin, immunoglobulin G (IgG) and fibrinogen. The ellipsometric-antibody detectability of the proteins on such surfaces were found to be variable, depending upon the location on the gradient and the order and combination in which the proteins were presented to the surface. Radiolabelled proteins were studied on discrete regions of these gradients. Competitive effects of albumin were found to be inhibitory (negative) with respect to IgG adsorption on hydrophobic surfaces, while enhancing IgG deposition on hydrophilic surfaces (positive). Scanning force microscopy in the so-called tapping mode indicates that proteins, particularly IgG, organize themselves differently with respect to surfaces, depending upon the nature of the surface and the presence of other proteins.