Kinetics of Human and Bovine Serum Albumin Adsorption at Silica-Titania Surfaces

The interaction of proteins with surfaces is important in separation and 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 is presently known about the relationship between amino acid sequence and binding. Here we report accurate measurements of the kinetics of adsorption of two closely homologous serum albumins (human and bovine) to a hydrated metal oxide surface, using an accurate integrated optics technique. Marked differences between the two proteins are observed. The results are analyzed using a model involving two bound forms, reversible and irreversible. The two forms are identified as two orientations of the protein with respect to the surface which make differing numbers 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 buffer for HEPES buffer causes dramatic changes in the adsorption, abolishing the irreversible mode completely for human serum albumin.