Inhibition of the enzymatic activity of thrombin by concanavalin A

Concanavalin A, a carbohydrate lectin derived from the jack bean, prolongs the thrombin clotting time of human plasma or purified fibrinogen. Prolongation is due to delay in peptide release from fibrinogen. The rate of fibrin monomer polymerization is not affected. Hydrolysis of protamine sulfate by thrombin is inhibited by concanavalin A. All inhibitory effects are prevented by α-methyl-D-mannoside. Concanavalin A does not delay clotting of fibrinogen by reptilase (releases fibrinopeptide A only) or by Ancistrodon contortrix contortrix (releases fibrinopeptide B initially followed by a small amount of A). It is concluded that concanavalin A binds to a carbohydrate on the thrombin molecule thus inhibiting its enzymatic activity.