CHEMISTRY OF COLLAGEN CROSS-LINKING - BIOCHEMICAL-CHANGES IN COLLAGENDURING THE PARTIAL MINERALIZATION OF TURKEY LEG TENDON

With age, the proximal sections of turkey leg tendons become calcified , and this phenomenon has led to their use as a model for collagen min eralization. Mineralizing turkey leg tendon was used in this study to characterize further the composition and crosslinking of collagen in c alcified tissues. The cross-link profiles of mineralizing collagen are significantly different from those of other collagenous matrices with characteristically low amounts of hydroxylysyl-pyridinoline and the p resence of lysyl-pyridinoline and pyrrolic cross-links. However, the p resence of the immature cross-link precursors previously reported in c alcifying tissues was not supported in the present study, and was foun d to be due to the decalcification procedure using EDTA. Analysis of t endons from young birds demonstrated differences in the crosslink prof ile which indicated a higher level of hydroxylation of specific triple -helical lysines involved in cross-linking of the proximal tendon. Thi s may be related to later calcification; suggesting that this part of the tendon is predestined to be calcified. The minimal changes in lysy l hydroxylation in both regions of the tendon with age were in contras t with the large changes-in the cross-link profile, indicating differe ntial hydroxylation of the helical and telopeptide lysine residues. Ch anges with age in the collagen matrix, its turnover and thermal proper ties in both the proximal and distal sections of the tendon clearly de monstrate that a new and modified matrix is formed throughout the tend on, and that a different type of matrix is formed at each site.