KINETICS OF HUMAN AND BOVINE SERUM-ALBUMIN ADSORPTION AT SILICA-TITANIA SURFACES

The interaction of proteins with surfaces is important in separation a nd purification procedures as well as in metabolism and its regulation . The degree of binding to a given surface in principle depends on the precise amino acid composition of the protein, although very little i s presently known about the relationship between amino acid sequence a nd binding, Here we report accurate measurements of the kinetics of ad sorption of two closely homologous serum albumins (human and bovine) t o a hydrated metal oxide surface, using an accurate integrated optics technique, Marked differences between the two proteins are observed, T he results are analyzed using a model involving two bound forms, rever sible and irreversible, The two forms are identified as two orientatio ns of the protein with respect to the surface which make differing num bers of hydrogen bonds to the surface, These numbers were estimated on the basis of the measured desorption rate constants, The interfacial binding energy was calculated from the quotient of the adsorption and desorption rate constants and compared with the value calculated from surface energy available data, Remarkably, substitution of phosphate b uffer for HEPES buffer causes dramatic changes in the adsorption, abol ishing the irreversible mode completely for human serum albumin. (C) 1 997 Academic Press