A fibrinopeptide is a short peptide released from fibrinogen during its proteolytic conversion toward fibrin. The principal forms are Fibrinopeptide A and Fibrinopeptide B, cleaved from the amino-terminal regions of the A-alpha and B-beta chains, respectively. Their removal exposes molecular sites that promote fibrin assembly.[ref]
Steady state kinetic parameters for the thrombin-catalyzed conversion of human fibrinogen to fibrin by D. L. Higgins and others. 1983, abstract: chain identity and thrombin-mediated peptide release
Experiments measured the release of the two fibrinopeptides separately and related their kinetics to fibrin polymerization. Under the tested solution conditions, release of Fibrinopeptide A preceded the main release of Fibrinopeptide B, with assembly affecting the later step.[ref]
Steady state kinetic parameters for the thrombin-catalyzed conversion of human fibrinogen to fibrin by D. L. Higgins and others. Abstract: predominant pathway and polymerization-dependent release
The small released fragments and the remaining network-forming material have different roles. For a stipulated counting example, if each converted fibrinogen molecule releases two copies of one fibrinopeptide, converting 3 nmol generates 6 nmol of that fragment. The amount recovered can report the extent of cleavage; it does not by itself determine the final clot's stiffness or network geometry.
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