CHARACTERIZATION OF THE INTERACTIONS BETWEEN LYSOZYME AND N-ALKYLTRIMETHYLAMMONIUM BROMIDES BY ZETA-POTENTIAL MEASUREMENTS

A detailed study of the adsorption of the n-alkyltrimethylammonium bro mides (C(n)TAB) to lysozyme by measurements of the zeta potential (zet a-potential) has been realized as a function of concentration and pH. While at pH 3.2 the zeta-potential of lysozyme remains positive in the presence of surfactants, at pH 7 and 10 the alkylammonium ions affect the zeta-potential causing a change in the neighbourhood of the point of zero charge (pzc) from negative to positive values. From the pzc w e have calculated Gibbs energies of adsorption and compared them with Gibbs energies of binding determined by equilibrium dialysis. The resu lts are similar, showing that the zeta-potential technique can be usef ul in a study of the interactions of proteins with amphiphilic ligands .