IDENTIFICATION OF LYSINE-DERIVED CROSS-LINKS IN PORCINE COLLAGEN TYPE-X FROM GROWTH-PLATE AND NEWLY MINERALIZED BONE

Intact collagen type X cannot readily be extracted from the growth pla te. Both the use of pepsin to release this molecule from tissue and th e relative solubility of collagen type X following treatment of chick embryos with beta-aminopropionitrile (Chen et al., 1992) suggest that the insolubility may by brought about by the formation of lysine-deriv ed crosslinks. By immunocytochemical labelling using antibodies specif ic for collagen type X, we have shown that this collagen type persists in the cartilaginous spicules present in metaphyseal bone and appears to be colocalized with collagen type II. The combined concentration o f the reducible bifunctional crosslinks, dihydroxylysinonorleucine and monohydroxylysinonorleucine, in collagen typeX isolated from the prem ineralized and newly mineralized growth plate was about 0.6 residues/m olecule, a level which might explain the relative intractability of co llagen type X. Pyridinoline and deoxypyridinoline were present in very small amounts in collagen type X; this suggests that, unlike the situ ation in other types of collagen, few of the bifunctional crosslinks u ndergo maturation to pyridinium compounds. Although it is clear that c ollagen type X contains lysine-derived crosslinks, work is in progress to establish which molecule also participates in the formation of the se crosslinks.