Binding of n-alkyl sulphates to lysozyme in aqueous solution

Abstract

The binding of a homologous series of n-alkyl sulphates to lysozyme has been measured by equilibrium dialysis at 25°C. The binding isotherms show a concentration dependence attributable to aggregation of the protein–surfactant complexes. Both sodium n-dodecyl and n-decyl sulphates give binding isotherms characteristic of specific high energy interactions at low free surfactant concentrations. These are followed by non-specific cooperative binding. Sodium n-octyl sulphate interacts only cooperatively with lysozyme. The binding isotherms are discussed in terms of the binding potential concept of Wyman and are used to calculate an apparent Gibbs energy of binding per surfactant anion as a function of the number of surfactant anions bound.