The amino acids that constitute sequence gamma 268-282 of fibrinogen are not involved in fibrin monomer polymerization.

Congenitally abnormal fibrinogens with impaired fibrin monomer polymerization have been described to contain single amino-acid substitutions localized in certain positions of the gamma 275-330 peptide region. To evaluate the role of the amino-acid sequence in the vicinity of Arg275 in fibrin monomer polymerization, the peptide fragment corresponding to gamma 268-282 was synthesized and used to obtain peptide-specific antibodies. These antibodies, when purified immunochemically on the immobilized peptide, bound to the intact fibrinogen and fibrin monomers with the same binding affinity. However, they did not recognize the gamma 268-282 epitopes on the denatured and reduced fibrinogen molecules. The lack of influence of antipeptide antibodies on fibrin monomer polymerization indicates that the gamma 268-282 peptide is not directly involved in the structure of the polymerization site in the D domain of fibrinogen. It is suggested that substitution of Arg275 either by His or Cys in abnormal fibrinogens results probably in conformational changes which disturb a proper orientation of the polymerization site and reduce its expression.