Abstract
The techniques of differential scanning calorimetry and electron microscopy were combined to locate collagens with different thermal stabilities in bovine dermis. When calfskin was heated at 1.25°c/min, denatured cores developed in the fibrils at 65°c, leaving native-banded sheaths. Coincident with the initiation of shrinkage and loss of molecular orientation at 68°c, the sheaths of the fibrils began to be denatured at distributed sites along the fibrils. At 80°c the collagen lost its organized fibrillar structure. When thermally labile crosslinks had been stabilized by reduction with borohydride, an endotherm lying above 66°c was suppressed, with proportional lowering of the total enthalpy change, and a fibrous texture revealing a helical subfibrillar structure remained. The three populations of collagen are located in the same fibrils. One, located in the cores of the fibrils, is half denatured at 68°c. Another, established by crosslinks, is competent to sustain the regular appearance of fibrils even after 56% of the collagen in them has been denatured. This population is located as sheaths at the peripheries of the collagen fibrils. A third, denaturing below 59°c, is codistributed with one or both of the two others.