Covalent structure of collagen: amino acid sequence of alpha 1(III)-CB9 from type III collagen of human liver.

The peptide alpha 1(III)-CB9 was prepared and purified from human liver, and its amino acid sequence was determined. Automated Edman degradation of the intact peptide and peptides derived from selective cleavage with hydroxylamine and digestions with trypsin, thermolysin, and Staph V8 protease enabled determination of the complete amino acid sequence. The peptide alpha 1(III)-CB9 represents the COOH terminus of the helical (pepsin-resistant) portion of type III collagen and terminates in a Cys-Cys sequence responsible for the intramolecular disulfide cross-linkages with other chains. The present work completes the entire amino acid sequence of the helical (pepsin-resistant) portion of human cirrhotic liver type III collagen consisting of peptides alpha 1-(III)-CB3-7-6-1-8-10-2-4-5-9. The COOH terminus of human liver alpha 1(III) contained two additional triplets which, together with the extra triplet at the NH2 terminus in alpha 1(III)-CB3, make the helical portion of type III collagen longer than alpha 1(I) by nine residues (three Gly-X-Y triplets). The helical region of human liver type III collagen, therefore, consists of 1023 amino acids or 341 triplets.