ISOLATION AND CHARACTERIZATION OF PEPTIDES DERIVED FROM ALPHA 1 CHAIN OF CHICK BONE COLLAGEN AFTER CYANOGEN BROMIDE CLEAVAGE

Cleavage of the α1 chain of chick bone collagen with CNBr gives rise to ten peptides which have been separated by ion-exchange and molecular sieve chromatography. The peptides constitute unique portions of the α1 chain as demonstrated by chromatographic properties, amino acid composition, and molecular weight. They account for all of the amino acids in the α1 chain. The molecular weights of the peptides vary from 242 to 26,000 and total 92,000, in good agreement with the measured molecular weight of about 95,000 for α chains. The isolation of ten unique peptides in approximately equimolar amounts from a chain containing nine methionyl residues indicates that the two α1 chains of the bone collagen molecule have identical or very similar primary structures. Variation in the degree of hydroxylation of lysine is evident from the presence of nonintegral numbers of hydroxylysyl and lysyl residues in many of the peptides. The peptide from the cross-link region, α1-CB1, contains a lysyl residue (amino acid number 7 from the NH2terminus) which is about 50% hydroxylated. Cleavage of this peptide with trypsin demonstrated that hydroxylysine and lysine occupy the same position. Heterogeneity of this type cannot be the result of differences in the original primary structure, but arisesafter synthesis of the protein. The CNBr peptides derived from the α1 chain of chick bone collagen are clearly homologous to those obtained previously from the α1 chain of rat skin collagen. An apparent exception was noted in that a dipeptide (α1-CB0) was present in digests of the α1 chain of chick bone collagen that was not among the cleavage products of rat skin collagen α1. α1-CB0 was placed at the NH2-terminal end of the al chain, preceding α1-CB1. These two residues, plus two additional residues at the NH2-terminal end of α1-CB1 not found in rat skin collagen α1-CB1, placed the lysyl residue that is a precursor of crosslinks at position 9 in the α1 chain of chick bone collagen. Other than the addition of these four residues, the cross-link region of the chick bone collagen al chain, as represented by α1-CB1, is identical with the same region in rat skin collagen α1 except for an alanineserine substitution. The COOH-terminal peptide from rat skin collagen α1 (α1-CB6) is represented by two peptides (α1-CB6A and α1-CB6B) from chick bone collagen α1 indicating the presence of an extra methionyl residue in the COOHterminal region. © 1969, American Chemical Society. All rights reserved.