Interaction between sodium n-undecyl sulfate and insulin

The binding of sodium n-undecyl sulfate with bovine insulin was studied at pH 3.2 and 10 by equilibrium dialysis at 25°C. The binding data have been used to determine the Gibbs energies of interaction using the theoretical model of the Wyman binding potential. The curves of Gibbs energies as a function of the number of bound ligands (ν) tend to limiting values of around -14 kJ mol^-1 at high values of ν. The enthalpies of in interaction have been measured directly by microcalorimetry showing an increase of exothermicity at lower pH. The results have been compared with similar data for the interaction of anionic surfactants with insulin.