Cross Linked C-Telopeptide Of Type III Collagen (CTXIII)

Several peptides were isolated from tryptic digests of insoluble calf aorta matrix by chromatography. Reductive pyridylethylation of a tryptic 15 kDa pool released fragments deriving from the C-terminus of type III collagen. A 50-residue peptide T-C(III) was shown by sequence analysis to be the C-terminal peptide from the alpha 1(III)-chain, containing a helical and non-helical region of equal sizes. The peptide was further digested with collagenase to give Col(C)(III), comprising the complete C-terminal non-helical region of alpha 1(III) including a hydroxylysine in position 16(C). The peptide T-C(III) x T-N(III) was isolated, demonstrating covalent cross-linking between the C-terminal non-helical region of one type III molecule and the N-terminal helical cross-linking region of another. Its digestion with cyanogen bromide yielded the small fragments alpha 1(III)CB3B and alpha 1(III)CB3C, confirming T-N(III) as an N-terminal helical cross-link site.