CHARACTERIZING KERATINS USING HIGH-PRESSURE DIFFERENTIAL SCANNING CALORIMETRY (HPDSC)

Applying differential scanning calorimetry (DSC) for temperatures up to 180-degrees-C, the denaturation transition of the alpha-helical material of various keratins in excess water was studied at conditions of equilibrium water vapor pressure (high-pressure DSC). The results show a generally cystine content and material invariate denaturation range of 20-30-degrees-C with peak temperatures around 140-degrees-C. Though analysis of variance and multiple comparison tests show a pronounced inhomogeneity of the enthalpy data, the results generally support the material invariance of the denaturation enthalpy and hence of the helix content of the keratins. The denaturation enthalpy for the helical coiled-coil-structures in the intermediate filaments is determined as DELTAH = 6.5-7.8 kJ/mol. A significant positive correlation was found between the denaturation temperatures and the cystine content. It is concluded, that the helix denaturation temperatures are kinetically controlled by the amount and/or the chemical composition of the surrounding nonhelical matrix, and that the double-peak endotherms observed for wool and other keratins originate from two cell types that are sufficiently different in sulfur content to allow endotherm separation. In the case of wool the cell types can be identified as ''ortho-'' and ''paracortical'' cells.