Cross-linking and stereospecific structure of collagen in mineralized and nonmineralized skeletal tissues

Molecular distributions of the intermolecular cross-links in fetal bovine bone type I collagen fibrils were quantitatively determined and compared with those of periodontal ligament. Results indicated that Hyl and Lys residues in the COOH-terminal nonhelical peptide portions (residues 16C) of both alpha 1 chains were quantitatively converted to aldehydes. These in turn stoichiometrically formed cross-links with residues Hyl-87 on both alpha 1 and alpha 2 chains of neighboring molecules. The ratio of cross-linked alpha 1 to alpha 2 chains was 3.5 to 1 indicating a stereospecific packing of collagen molecules in the fibrils similar manner to periodontal ligament collagen. It was found that there were few aldehyde derived cross-links in the NH2-terminal nonhelical portions of the bone type I collagen. The relative paucity of the cross-links in NH2-terminal region of bone collagens may favor mineralization.