SHORT-RANGE INTERACTION BETWEEN ADSORBED LAYERS OF HUMAN SERUM-ALBUMIN

The adsorption of human serum albumin (HSA) onto muscovite mica has be en investigated by means of surface force and ESCA measurements. The r ange of protein concentration explored was 0.001-1.0 mg/ml in 10(-3) M NaCl at pH 5.6. It was found that negatively charged albumin adsorbs onto negatively charged mica. Small structural changes are induced by the adsorption, and further structural changes can be induced by apply ing an external compressive force. The structure of the adsorbed layer depends on the surface density. As surfaces with a low adsorption den sity of HSA are brought together, the protein molecules are able to di ffuse along the surface, facilitating the merging of the two HSA layer s into one single HSA layer in the gap between the surfaces. At high s urface density crowding effects impede the rearrangement of the HSA la yers and two separate layers of HSA remain in the gap between the surf aces. An adhesion force is present at low-packing but not at high-pack ing densities. It was found that the short-range interaction between o ne HSA-coated surface and one bare mica surface was strongly attractiv e, demonstrating that the adhesion forces likely are induced by HSA mo lecules bridging between two surfaces and not by attractive interactio ns between the proteins themselves. (C) 1994 Academic Press, Inc.