Location of the intermolecular cross-links in bovine dentin collagen,solubilization with trypsin and isolation of cross-link peptides containing dihydroxylysinonorleucine and pyridinoline

³H]NaBH₄ reduced bovine dentin collagen was denatured at 60°C for 1 hr and then digested with trypsin. The digest was still substantially insoluble suspension, but it was found that 99% of dentin collagen can be solubilized if the digest was heated again at 60°C for 15 min. Two cross-linked tryptic peptides were isolated from this digest by sequential chromatographies on Sephadex G50, phosphocellulose and DEAE-cellulose column. One isolated peptide was characterized as a 59 residue cross-linked peptide including one residue of dihydroxylysinonorleucine and the other was 103 residue including one residue of pyridinoline. The amino acid compositions were consistent with the identification of the 59 residue peptide as the sequence in α1-CB4-5 (76–90) linked to the sequence in α1-CB6 (990-23^c), and the 103 residue peptide as the sequence 76–90 linked to two of the sequence 990-23^c. These results strongly support the previously proposed precursor-product relationship between dihydroxylysinonorleucine and pyridinoline.