The stability of collagen cross-links when derived from hydroxylsyl residues

The cross-linked cyanogen bromide peptide, (4×9), previously isolated after reduction of cartilage collagen, has been isolated without prior reduction of the collagen. The unreduced cross-link is cleaved by periodate allowing recovery of the component peptides. When isolated after borotritide reduction of the collagen, (4×9) contains a single residue of radioactive hydroxylysinohydroxynorleucine. Radioactivity in the cross-link remains in the component peptides when the cross-link is cleaved with periodate. Performic acid oxidation removes this radioactivity and produces an additional glutamic acid residue in each peptide. These data indicate that dehydrohydroxylysinohydroxynorleucine undergoes an Amadori rearrangement producing a more stable keto-amine form of the cross-link.