The effect of pH on the thermal stability of fibrous hard alpha-keratins

The study of the effect of pH on the behaviour of proteins is still a topic of interest. We here report an unexpected increase of thermal stability of hard alpha-keratins under the influence of pH that is observed when investigating their thermal behaviour by differential scanning calorimetry (DSC). The results, particularly for oxidatively damaged keratin fibres treated with low pH solution, show a significant increase of enthalpy and a shift of the peak temperature towards higher temperature for the endothermic process assigned to the thermal denaturation. We propose a three-phase model for describing the behaviour of fibrous hard alpha-keratins, in which the interface, made of non-helical tail domains of keratin, scaffolds the intermediate filaments and plays an important role. It is strengthen by the action of strong acids and controls the thermal properties of the alpha-helix. The approach is supported by amino-acid analysis, X-ray diffraction, Raman spectroscopy and tensile strength observations.