COMPARATIVE SEQUENCE STUDIES OF RAT SKIN AND TENDON COLLAGEN .2. ABSENCE OF A SHORT SEQUENCE AT AMINO TERMINUS OF SKIN ALPHA1 CHAIN

The amino acid sequence of rat tendon collagen is very similar but not identical with that of rat skin collagen. In addition to minor differences related to the hydroxylation of proline, the α1 chain of rat skin collagen lacks the tetrapeptide Glx-Met-Ser-Tyr which is present at the NH2terminus of the α1 chain of rat tendon collagen. This short sequence may be removed from the skin protein by a physiologic proteolytic mechanism or its existence may reflect the presence of different genes coding for tissue-specific collagen chains in the two tissues. However, limited proteolysis during extraction and purification of rat skin collagen cannot be excluded. If the primary structure and conformation at the NH2terminus of rat skin collagen differs in vivo, this modification could influence the aggregative properties and relative rates of cross-link formation of rat skin collagen vis-à-vis rat tendon collagen and play a role in collagen biogenesis. The possibility that several amino acids including glutamine (or pyrrolidone-5-carboxylic acid) are removed from the NH2terminus of a polypeptide chain is also of interest in view of the role which pyrrolidone-5-carboxylic acid may play in the initiation of polypeptide chain synthesis in higher organisms. © 1969, American Chemical Society. All rights reserved.