Relationship between proton and surfactant binding to lysozyme in aqueous solution

Abstract

The relationship between the binding of sodium n-dodecyl sulphate and protons to lysozyme has been investigated by equilibrium dialysis and titrimetry. The data cover the pH range 2.9–10.8 and surfactant concentrations up to 10.0 × 10^–3 mol dm^–3. A theoretical approach based on the binding potential concept of Wyman is presented and has been used to make estimates of the apparent Gibbs energies of binding of both protons and surfactant ions to the surfactant–lysozyme complexes.

The data imply that surfactant binding can induce protonation of carboxylic acid groups in the native conformation which subsequently ionise on unfolding of the protein. This effect gives rise to maxima in the titration curves at surfactant concentration in the region of protein unfolding.