Interaction of fibrinogen and asialofibrinogen with concanavalin A and clotting properties of the complexes.

Concanavalin A interaction with separate fibrinogen chains takes place through specific binding to mannopyranose residues of the carbohydrate attached to B beta and gamma chains. However, analysis of the binding data to whole molecules shows in the concentration range studied (up to 9 concanavalin A mol/fibrinogen mol), that there are only two binding sites per molecule and that the dissociation constant does not change by sialic acid removal. Ultracentrifugation studies show that at pH 7.8 and ionic strength 0.15 M, concanavalin A binds to fibrinogen and asialofibrinogen very probably as a polyvalent tetramer forming molecular aggregates that strongly suggest attachment of two concanavalin A tetramers per mol fibrinogen. This implies that two of the four possible sites in the fibrinogen molecule are not accessible to concanavalin A tetramers. Asialofibrinogen and its concanavalin A complexes coagulate twice as fast as those of fibrinogen. However, in both cases there is strong diminution of the aggregation rate induced by thrombin with concanavalin A binding at low relative lectin concentrations (less than 60 micrograms/mg fibrinogen). Higher concentrations that produce concanavalin A-mediated aggregation result in an apparent increasing coagulation rate. The final amounts of coagulated protein are not affected by concanavalin A nor the rate of fibrinopeptides cleaved by thrombin. Only the fibrin cross-linking capacity is diminished as concanavalin A concentration increases.