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

Protein-surfactant interactions play a key role in competitive adsorpt ion and desorption of adsorbed proteins by surfactants. The influence of nonmicellar solutions of an anionic surfactant, sodium dodecanesulf onate, on the interaction forces between preadsorbed layers of lysozym e on mica were investigated using the surface force apparatus. In the absence of surfactant, lysozyme adsorbs irreversibly and neutralizes t he 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 establish ed upon contact of the adsorbed layers. Surfactant binding increases t he interfacial charge and eliminates the adhesion force between opposi ng surfaces. Large-scale desorption or conformational change in respon se to surfactant binding is not observed, although partial desorption of the outer members of adsorbed dimers is induced at the highest surf actant concentration investigated.