Plasma inhibitors of the Hageman factor dependent pathways

The Hageman factor dependent pathways are influenced by several control proteins which modulate the extent of activation and biologic activity of these enzyme substrates (Fig. 1). C1 INH plays a prominent role by acting at the common initiating step for all three Hageman factor dependent systems and its deficiency produces disease in man. Alpha-2 macroglobulin appears to play an important role in the fibrinolytic sequence, having potent activity towards both plasminogen activator and plasmin. Antithrombin most prominently influences the state of activation of the coagulation sequence by regulating the enzymatic activities of activated Factors XI, IX and X and, most importantly, that of thrombin. Significantly, deficiency of antithrombin results in increased thrombosis in man.