Immunochemical evidence for intramolecular interaction of the carboxy terminal A alpha-appendages of plasma fibrinogen.

A monoclonal antibody (Mab), 45J, which reacts with intact fibrinogen, has been employed to demonstrate the interaction of the carboxy terminal regions of the A alpha-chain in non-denatured plasma fibrinogen. The 45J Mab recognizes an epitope in the mid section of the carboxy terminal end of the A alpha chain. The epitope is destroyed by plasmin and trypsin digestion. The 45J Mab and a horseradish peroxidase conjugate of the 45J Mab (45J-HRP) were used in an ELISA to demonstrate that the antibody could recognize two copies of the same epitope on purified fibrinogen or denatured plasma fibrinogen. Fibrinogen in non-denatured plasma could not be detected by this single antibody ELISA. This immunochemical study demonstrates that only one copy of the epitope on the C-terminal protuberance of the A alpha-chain is exposed in non-denatured plasma. However, once the plasma fibrinogen has been denatured, as in the purification process, both copies of the epitope are available for antibody binding. This finding suggests that in plasma there is an intramolecular interaction between the carboxy terminal ends of the fibrinogen A alpha-chains which can be destroyed by denaturation.