Immunological Characterisation of A∝ Chain Fragments of Human Fibrinogen

In an investigation of the early cleavage fragments resulting from fibrin(ogen)olysis, we have examined the nature of small peptides arising from the C-terminal part of the Aα chain of human fibrinogen.Antiserum to the carboxymethylated Aα chain of human fibrinogen has been prepared, and used to study the Aα-related antigens from (i) a plasmin digest of human fibrinogen, (ii) human serum, obtained from urokinase-treated normal plasma, and (iii) normal human serum. Using immunodiffusion and immunoelectrophoresis with anti-Aα antiserum, along with Polyacrylamide gel electrophoresis, at least two non-identical Aα -related antigens have been detected in a final plasmin digest of human fibrinogen. The largest of these antigens (MW 26,000) has been isolated and named Aα.-RA (26,000). This may be similar to the previously-described fragments, Hi2-Ala, fragment A or fragment H. Aα -related antigen has been produced by in vitro fibrinogenolysis in plasma and has been detected in the serum. In addition, small quantities of Aα -related antigen have been found in untreated normal human serum.These results suggest that anti-Aα antiserum is likely to be a useful reagent for the study of the early plasmin-derived fragments of fibrin(ogen)olysis in vitro and in vivo.