Abstract
The thermal shrinkage of the acid insoluble collagen fibers from rat-tail tendon occurred mainly on account of tropocollagens. The shrinkage coefficients of collagen sample length approximately agreed with those of the long periods which were determined by small-angle X-ray scattering. The structural change took place from the elementary to the higher level of the tendon hierarchy with increasing temperature. The thermal shrinkage is divided into the following three regions. Region 1 (room temperature-60°C): after the tropocollagen molecules shrink during heating, the shrinkage reversibly recovers during cooling. Region 2 (60-160°C): the microconformation of peptide group is distorted, thus, the conformation of the tropocollagen is slightly distorted. However, the slightly distorted structure is returned to the original when the water loss during heating is recovered, Region 3 (above 160°C): the tropocollagen molecules can no longer form the triple-helix, and the microfibrils are separated into bundles consisting of several microfibrils. However, the regularity of the long period formed by the microfibril is still maintained since the cross-linkage between tropocollagen molecules have not yet broken.
