INTERACTIONS OF PROTEINS WITH POLYELECTROLYTES AT SOLID LIQUID INTERFACES - SEQUENTIAL ADSORPTION OF ALBUMIN AND HEPARIN/

The association of heparin with the surface-immobilized albumin exhibi ts a strong pH dependence governed by the protonization of albumin. At neutral pH the interaction is quite weak but at acidic pH and especia lly below the isoelectric point of albumin the interaction becomes pro nounced: 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 stat e of charge equivalence. The dependence of heparin binding on the ioni c strength shows an inexpressive maximum in ca. 0.2 M NaCl (pH 4.0), a pparently due to a less extended conformation of heparin. The primary albumin monolayer adsorbed on a solid support by hydrophobic interacti on can serve as an anchor for the sequential adsorption of alternating monolayers of heparin and albumin and thus multiple layers with a san dwich-like architecture are deposited on the surface, The adsorption i n each step reaches saturation determined by the charge equivalence an d the composition of the bilayers tends to be the same regardless of t heir distance from the surface. The approach described makes it possib le to cover surfaces with a regular multilayer of a required and unifo rm thickness. (C) 1997 Academic Press.