| Abstract: | A study on the titration behaviour of hen's egg lysozyme (LSZ) and milk α-lactalbumin (LAC) is presented. Titration curves for the proteins in their native state, after exposure to denaturing agents, and adsorbed on poly(styrenesulphonate) (PSS) latices are compared. Titrations of the proteins in the presence of guanidinium hydrochloride and sodium dodecyl sulphate (SDS) show that electrostatic interactions, more than alterations in the chemical environment, affect the dissociation of the charged groups on the protein molecule. The titration of adsorbed (apo)-LAC is similar to that of the SDS-denatured state, independent of the surface coverage. The titration of LSZ depends on the degree of coverage, suggesting different modes of adsorption. The two conformers of LAC, i.e. apo-LAC and Ca-LAC, are compared to test the influence of the structural stability of the protein on the titration behaviour. In solution, the two conformers of LAC titrate differently, but after adsorption on to a PSS latex surface the titration behaviour is practically the same. This points to a similar adsorbed state, with expulsion of the Ca2+ ion from the Ca-containing form. |
