The locations of collagens with different thermal stabilities in fibrils of bovine reticular dermis.

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 degrees C/min, denatured cores developed in the fibrils at 65 degrees C, leaving native-banded sheaths. Coincident with the initiation of shrinkage and loss of molecular orientation at 68 degrees C, the sheaths of the fibrils began to be denatured at distributed sites along the fibrils. At 80 degrees C the collagen lost its organized fibrillar structure. When thermally labile crosslinks had been stabilized by reduction with borohydride, an endotherm lying above 66 degrees 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 degrees 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 degrees C, is codistributed with one or both of the two others.