Isolation and structure of the amino-terminal cross-linking region in insoluble type III collagen.

A collagenous peptide T1X was isolated from a tryptic digest of the insoluble matrix of calf skin. The peptide consists of two identical polypeptide chains each with a length of 72 amino acid residues joined by a cross-link. Absorption spectra obtained from hydrazone and azine derivatives of T1X indicated that the peptide contains an aldol-type of cross-link (X). The sequence of 23 amino acid residues in the amino-terminal region was determined as Glx-Tyr-Glu-Ala-Tyr-Asp-Val-X-Ser-Gly-Val-Ala-Gly-Gly-Gly-Ile-Ala-Gly-Tyr-Hyp-Gly-Pro-Ala. This sequence overlaps the previously described amino-terminal sequence of alpha1 (III) chain obtained from pepsin treated, insoluble type III collagen. Thus, the present data demonstrate a nonhelical segment of 14 amino acid residues in type III collagen important for cross-linking.