Cation-promoted adsorption of proteoheparan sulphate

Abstract

The adsorption of proteoheparan sulphate, a strongly negatively charged proteoglycan, was investigated. It was found that heparan sulphate without any protein component does not adsorb in itself, either to hydrophilic or hydrophobized silica surfaces. Additions of excess electrolyte alone do not affect this behaviour. In the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB), however, adsorption occurs, presumably as polyelectrolyte-surfactant complexes. In the presence of excess electrolyte, the tendency for adsorption of the polyelectrolyte-surfactant complex is strongly increased. However, this effect cannot be satisfactorily explained by electrostatics alone. The native proteoheparan sulphate, however, does adsorb at hydrophobic surfaces, presumably via the hydrophobic domains of its protein core. On addition of CaCl 2, the adsorbed amount increases strongly, analogous to the CTAB-heparan sulphate complex. For both proteoheparan sulphate and the CTAB-heparan sulphate complex, the adsorption and desorption processes are slow and the desorption on dilution is far from complete.