Type XII collagen is expressed in embryonic chick tendons. Isolation of pepsin-derived fragments

Two new disulfide-bonded collagenous pepsin-derived fragments have been isolated from chick embryo tendons. These fragments represent less than 0.5% of the pepsin-extractable collagen. We purified 10- and 16-kDa reduced fragments derived, respectively, from 32- and 46-kDa disulfide-bonded fragments. Unique tryptic peptide maps were obtained for each fragment. Although these collagenous fragments differ from all the known collagens in their electrophoretic behaviors, tryptic peptides and amino acid compositions, they present some striking similarities with the pepsin-derived fragments from cartilage type IX collagen. Unique sequences from the amino terminus and from a tryptic peptide were obtained for the 10-kDa reduced fragment, demonstrating that this fragment is derived from type XII collagen, whose existence had only been inferred so far from a cDNA encoding it.