Development of an immunoassay for the COOH-terminal region of the gamma chains of human fibrin

A COOH-terminal peptide involved in the crosslinked region of the γ-chains of human fibrin has been isolated for use in a radioimmunoassay. The crosslinked γ-chains (γ-dimer) were purified by ion-exchange chromatography following reduction and carboxymethylation of human fibrin. After digestion with CNBr followed by gel filtration, the 54 amino acid COOH-terminal, crosslinked peptide was finally purified by ion-exchange chromatography on SP-Sephadex. The peptide's identity was confirmed by amino acid analysis and NH 2-terminal sequence determination. It was coupled to thyroglobulin to be employed as an immunogen, and the resulting antisera have been used to develop a radioimmunoassay to measure the immunoreactivity of this region in its monomeric and dimeric forms. By employing this immunogen it has become possible to raise antisera which react preferentially with the crosslinked γ-γ form of this peptide.