[Thermal denaturation of collagen in solutions and fibrils].
Thermal denaturation of rat skin collagen in fibrils and water solutions has been studied by differential scanning calorimetry. Heating rates in the range 0.3-25 K/min were used. For collagen solutions with concentrations higher than 10% the amount of heat absorbed at denaturation was found to be strongly dependent on the heating rate. Heat absorption is maximum at fast heating. Lowering of the heating rate decreases the heat absorption. At sufficiently low heating rates the magnitude of denaturation heat effect depends on the heating rate only slightly. For diluted solutions and fibrils the denaturation heat is independent of heating rate and was estimated to be 20 +/- 2 cal/g, in good agreement with other published data. This value is close to denaturation heat of concentrated solutions at fast heating. We have assumed that the decrease of denaturation heat in concentrated solutions at slow heating is caused by the exothermic process of postdenaturation protein aggregation. Proper values of denaturation enthalpy for isolated molecules can be measured only at fast heating. In fibrils and diluted solutions postdenaturation is not important. In diluted solutions there is no interaction between the protein molecules. In fibrils the protein molecules are closely packed with strong lateral cross-linking which freezes molecular mobility and inhibits the postdenaturation aggregation.