EFFECT OF ANIONIC SURFACTANT ON INTERACTIONS BETWEEN LYSOZYME LAYERS ADSORBED ON MICA

Protein-surfactant interactions play a key role in competitive adsorption and desorption of adsorbed proteins by surfactants. The influence of nonmicellar solutions of an anionic surfactant, sodium dodecanesulfonate, on the interaction forces between preadsorbed layers of lysozyme on mica were investigated using the surface force apparatus. In the absence of surfactant, lysozyme adsorbs irreversibly and neutralizes the negative mica surface charge. The force profile indicates that the adsorbed layer is heterogeneous and deformable, consisting of protein monomers and loosely associated dimers. An adhesion force is established upon contact of the adsorbed layers. Surfactant binding increases the interfacial charge and eliminates the adhesion force between opposing surfaces. Large-scale desorption or conformational change in response to surfactant binding is not observed, although partial desorption of the outer members of adsorbed dimers is induced at the highest surfactant concentration investigated.