Conversion of fibrinogen to fibrin induced by preferential release of fibrinopeptide B.

Fibrin clot-promoting enzyme preferentially releasing fibrinopeptide B from fibrinogen was isolated from the crude venom of Agkistrodon contortrix and its mode of action was studied in detail. A purification procedure involving affinity chromatographies on immobilized lectin and arginine removed plasmin-like and kallikrein-like activities towards low-molecular-weight chromogenic substrates. Fibrin-promoting enzyme cleaved off only fibrinopeptides A and B from fibrinogen. The initial relative rate of release of fibrinopeptide B/fibrinopeptide A depended strongly on the presence of Ca 2+ . In the absence of Ca 2+ the amount of fibrinopeptides released by fibrin-promoting enzyme at the gel point was greater. Fibrinopeptide B was no longer released before fibrinopeptide A from the non-polymerizing N-terminal disulphide knot of fibrinogen. Catalyzed by activated factor XIII, complete γ -dimer and α -polymer formation was observed in fibrin from which only 23% of fibrinopeptide A, but 100% of fibrinopeptide B was released by fibrin-promoting enzyme, γ -dimer formation markedly preceded α -polymer formation. These results strongly imply a similar overall arrangement of monomer molecules in this fibrin when compared with a thrombin-induced fibrin in which fibrinopeptide A is released before fibrinopeptide B. These observations support the concept that on fibrinopeptide B release from fibrinogen polymerization sites are exposed which reinforce the sites exposed on the release of fibrinopeptide A.