The action of tetranitromethane on acid-soluble tropocollagen

Treatment of dilute solutions of acid-soluble calfskin collagen with tetranitromethane at pH 8.0 resulted in the nitration of all the tyrosine residues in tropocollagen without precipitation of the modified protein. Amino acid analysis of the product showed (a) that no other amino acids were affected and (b) that the 3-nitrotyrosine formed accounted for only 30% of the tyrosine originally present in the molecule. This indicated that some of the tyrosine residues were involved in a reaction which did not produce 3-nitrotyrosine. Polyacrylamide gel electrophoresis, viscometry, and sedimentation analysis of the product showed the formation of predominantly intra-molecular cross-links. However, intermolecular cross-links were also formed but to a limited extent.