Enthalphy changes associated with the denaturation of collagens of different imino acid content

The enthalpy changes associated with the denaturation of acid-soluble and insoluble collagens prepared from sheep, cod, halibut and pike skin were determined by differential scanning calorimetry. The enthalpy change associated with the soluble collagens decreased with decreasing imino acid content (from 1420 cal/mol for sheep to 736 cal/mol for cod) while the value for insoluble collagens was approximately constant at 1360 cal/mol. A possible explanation for these values in terms of the nautre of the bonds present in collagen is discussed.