PROTEIN ADSORPTION AT THE AGI-WATER INTERFACE

The adsorption of hen's egg lysozyme (LSZ) and milk alpha-lactalbumin (LAC) on colloidal AgI is described. These two proteins have similar s hapes and sizes, but different structural stabilities and isoelectric points. The charge at the silver iodide surface is determined by the c oncentration of I- (or, for that matter, Ag+), whereas that at the pro tein surface is controlled by the pH. The influence of electrostatics on adsorption is studied by varying the pi, pH, and ionic strength. De sorption experiments show that LAC adsorbs more irreversibly than LSZ. Analysis of calorimetric data suggests that the adsorption of LAC doe s not depend on the surface coverage, whereas the adsorption of LSZ do es. Proton titrations reveal, for both proteins, a strong influence of the adsorption on the titration behavior of the carboxyl groups. An e stimation of the coadsorption of ions is presented by comparing proton titration and electrophoretic mobility data. (C) 1995 Academic Press, Inc.