INTERNALIZATION OF THE AMINO TERMINAL 1-78 SEQUENCE OF THE GAMMA-CHAIN OF NATIVE FIBRINOGEN AND EXPOSURE ASSOCIATED WITH CATABOLISM AND PLASMIN CLEAVAGE

Specific antibodies of the γ1-78 peptide of human fibrinogen were employed in binding assays and in equilibrium competitive inhibition assays to analyze the expression of γ1-78 antigenic determinants as an indication of the relative exposure of the γ1-78 sequence in the E domain of fibrinogen, high solubility fibrinogen subfractions I-8 and I-9, and plasmic cleavage fragments of fibrinogen and fibrin. A very limited exposure of γ1-78 sequences was found to occur concomitant with proteolytic deletions of the major carboxyterminal segment of the Aα chains in fgI-8, fgI-9. Exposure of γ1-78 is not influenced by further proteolysis to fg-X which is associated with Bβ1-43 deletion. Further proteolysis to fg-Y, which is associated with deletion of β43-53 and of one of the D domains, is associated with additional exposure of γ1-78. This is not significantly influenced by further proteolysis to fg-E with deletion of the second D domain, deletion of Aα1-19, and proteolysis at the carboxyterminal aspects of the E domain chains. © 1979.