Carboxyterminal Antigenic Determinants of Collagen from Calf Skin

The prevalent antibody response in the rabbit to acid‐soluble calf collagen is specifically directed to sites on the C‐terminal cyanogen bromide peptides α1‐CB6 a , α1‐CB61 b and α2‐CB (3.5). Three different antigenic determinants each unique for one of these peptides could be defined serologically. After tryptic cleavage of α1‐CB6 a or α1‐CB6 b the full serologic activity was found on peptides composed of 39 and 28 amino acid residues, respectively. The center of the antigenic determinants could be located around a tyrosine residue in the nonhelical sequence of these peptides. Chymotrypsin which cleaved at this point completely abolished the serologic activity. Evidence is provided that α1‐CB6 b is derived from α1‐CB6 a by loss of 18 amino acid residues from the C‐terminal end. Therefore, the antigenic determinant on α1‐CB6 b might be artificially created by tissue proteases. During this process a loss of activity for the antigenic determinant on α1‐CB6 a was observed. Extraction of the collagen polypeptide chains with 8M urea prevented this degradation and revealed in comparison to α1‐CB6 a an additional C‐terminal tyrosine residue.