Interactions of proteins with polyelectrolytes at solid/liquid interfaces: Sequential adsorption of albumin and heparin

The association of heparin with the surface-immobilized albumin exhibits a strong pH dependence governed by the protonization of albumin. At neutral pH the interaction is quite weak but at acidic pH and especially below the isoelectric point of albumin the interaction becomes pronounced: about 0.42 g of heparin is bound per 1 g of albumin at pH 3. The stoichiometry of the complex at saturation corresponds to the state of charge equivalence. The dependence of heparin binding on the ionic strength shows an inexpressive maximum in ca. 0.2 M NaCl (pH 4.0), apparently due to a less extended conformation of heparin. The primary albumin monolayer adsorbed on a solid support by hydrophobic interaction can serve as an anchor for the sequential adsorption of alternating monolayers of heparin and albumin and thus multiple layers with a sandwich-like architecture are deposited on the surface, The adsorption in each step reaches saturation determined by the charge equivalence and the composition of the bilayers tends to be the same regardless of their distance from the surface. The approach described makes it possible to cover surfaces with a regular multilayer of a required and uniform thickness. (C) 1997 Academic Press.