Plasma contains the precursor of a carboxypeptidase B-like enzyme. This zymogen can be activated by high levels of thrombin, such as those that occur after clot formation, or by low levels of thrombin in the presence of thrombomodulin. The activated enzyme suppresses fibrinolysis by removing carboxy terminal lysine residues from partially degraded fibrin, thereby preventing plasmin-mediated positive feedback in the fibrinolytic cascade. The existence of this protein implies a direct molecular link between the coagulation and fibrinolytic cascades through the thrombin-thrombomodulin complex. This connection most likely plays a significant role in maintaining a proper balance between the deposition and removal of fibrin.