AGE-RELATED THERMAL-STABILITY AND SUSCEPTIBILITY TO PROTEOLYSIS OF RAT BONE-COLLAGEN

The shrinkage temperature (T(s)) and the pepsin-solubilizability of collagen fibrils in bone matrix obtained from decalcified femur diaphysis from 2-, 5-, 15- and 25-month-old rats were found decrease with age. Digestion with human fibroblast collagenase dissolved less than half of the collagen, whereas sequential treatment by pepsin followed by collagenase resulted in its complete dissolution. This result shows that collagenase and a telopeptide-cleaving enzyme, when acting in an appropriate sequence, have a great potential for the degradation of bone collagen. The 'melting' profile of the pepsin-solubilized collagen showed a biphasic transition peaks at 35.9-degrees-C and 40.8-degrees-C. With increasing age an increasing proportion of the collagen 'melted' in the transition peak at 35.9-degrees-C (pre-transition), and the 'melting' temperature (T(m)) of the collagen decreased in parallel with T(s) in relation to age. Both T(s) and T(m) decreased by 3-degrees-C in the age span investigated. The age-related change in T(s) could therefore be accounted for by the decrease in molecular stability. The collagenase-cleavage products of the bone collagen obtained by the sequential treatment with pepsin and collagenase showed only one peak transition (at 35.1-degrees-C), and the T(m) for the products was independent of age. The results indicate that the pre-transition for the pepsin-solubilized collagen is due to an age-related destabilizing conformational change of the collagen molecule in the proximity of the collagenase-cleavage site. The age-related decrease in thermal stability may have implications for the mechanical strength and turnover of the bone collagen. In contrast with bone collagen, soft-tissue collagen showed neither the age-dependency of thermal stability nor the characteristic biphasic 'melting' profile.