ADSORPTION OF LYSOZYME AND ALPHA-LACTALBUMIN ON POLY(STYRENESULPHONATE) LATICES .1. ADSORPTION AND DESORPTION BEHAVIOR

In this paper, the adsorption of hen's egg lysozyme (LSZ) and milk alpha-lactalbumin (LAG) on poly(styrenesulphonate) (PSS) latices of different surface charge densities is presented. Adsorption isotherms were studied as a function of the pH and the ionic strength. Unusual high protein adsorptions are detected for this polymer, which may be due to a non-rigid ''loopy'' surface of the latex particle. The adsorption of the proteins on the PSS latice is influenced by various types of interactions, but the adsorption capacity is mainly determined by the intermolecular electrostatic interaction. In contrast to apo-LAC, a fraction of the LSZ molecules are electrostatically reversibly adsorbed. In order to asses the influence of the structural stability of the protein, the adsorption of two conformers of LAC has been studied, i.e. apo-LAC and Ca-LAC. The structural stability of the LAC molecule depends strongly on the presence of a Ca2+ ion bound to the protein. On the (hydrophobic) PSS latex surface, however, practically no difference in the adsorption of the two conformers is observed, suggesting that structural perturbation occurs in the LAC molecule causing release of the Ca2+ ion.