The Covalent Structure of Collagen

The amino acid sequences of chick skin al-CB4 and al-CB5 have been determined by automated Edman degradation of the intact peptides and of their tryptic and chymotryptic peptides. The two peptides contain 47 and 37 residues and comprise residues 56 to 102 and 103 to 139, respectively, of the al(I) chain. In addition, al-CB5 is the major hexose-containing peptide, previously reported to be active in mediating platelet aggregation. A comparison of the sequence with previously reported data on the homologous region of the rat skin al(I) chain indicates that there are only three interspecies differences, or a sequence identity of 96%. Although the amino acid sequence of an al(I) chain can be constructed by combining the data obtained from the CNBr’ peptides (1, 2) of rat and calf skin collagens (3), as yet the complete sequence is not known for any of the cy chains from a single species or tissue. As a part of our systematic effort to determine the complete amino acid sequence of chick skin collagen, we have previously completed sequence determina- tions on al-CBl, al-CB2, al-CB3, al-CB7, el-CBGA, LUP-CBl, and (~2-cB2 peptides of chick skin collagen (4-8). In the present paper, we report our data delineating the covalent structure of (rl-CB4 and the adjacent glycopeptide, al-CB5. These two peptides together comprise residues 56 through 139 of the more than 1000 residues of the al(I) chain. The amino acid sequence of al-CB4 of rat skin collagen was previously published by Butler and Ponds (9). In addition, the covalent structure of al-CB5 is of particular interest, for we have found that the glycopeptide from chick skin collagen interacts with human platelets and causes them to aggregate (10, 11). Further studies indicate that the effect is mediated through the “platelet release reaction” induced by the glycopeptide (12). Since the homologous glycopeptide of rat skin collagen does not possess the platelet-aggregating property (ll), it was of interest to study the detailed covalent structure of the chick peptide for comparison with the rat *This investigation was supported by Grants AM 16506 and AM 3564 from the United States Public Health Service and by grants from the Gebbe Research Foundation and the Memphis and