Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombin, the final enzyme of the coagulation system, also influences profibrinolytic activity by several mechanisms. These include cellular release of tissue plasminogen activator, activated protein C-induced fibrinolysis, and inactivation of plasminogen activator inhibitor, type 1 (PAI-1). In this report, the role of thrombin in the regulation of PAI-1 is investigated. Our studies demonstrate that thrombin inactivation of PAI-1 occurs via an enzymatic mechanism rather than an enzyme-inhibitor complex mechanism. Evidence to support this conclusion is: (1) concomitant analysis of PAI-1 and thrombin activities demonstrate decreased PAI-1 activity but no loss of thrombin activity; (2) no visible thrombin--PAI-1 complexes by SDS-PAGE analysis; and (3) lack of formation of 125I-thrombin-PAI-1 complexes. Thrombomodulin, a thrombin binding cofactor that modifies thrombin's functions, did not influence the inactivation of PAI-1 by thrombin. We propose that thrombin enzymatically inactivates PAI-1 without forming a stable enzyme-inhibitor complex. The reaction is not affected by thrombomodulin. Overall this reaction occurs so slowly that it is not physiologically relevant without some modifying factor(s).
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PMID:Thrombin and the thrombin-thrombomodulin complex interaction with plasminogen activator inhibitor type-1. 165 27

The changes in coagulation and fibrinolysis were studied in cases of hepatocellular carcinoma with (n = 20) and without (n = 8) transcatheter hepatic arterial embolization (TAE). The plasma levels of thrombin-antithrombin III complex (TAT) and alpha 2 plasmin inhibitor complex (PIC) were significantly elevated after TAE, concurrently with a decrease in antithrombin III and antiplasmin (alpha 2-plasmin inhibitor) levels. The elevation of TAT was most significant (2.4-fold of the pre-TAE level) on day 3, whereas that of PIC was relatively less (1.3-fold on day 3). Tissue plasminogen activator in blood was also significantly increased on day 1, but it was decreased thereafter, although plasminogen activator inhibitor (PAI) remained high for at least 7 days after TAE. In contrast, such hematological changes were not observed in patients without TAE. Thus, both coagulation and fibrinolysis were activated after TAE, but its effect on fibrinolysis was less prominent, due probably to the increased synthesis of PAI.
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PMID:Effects of transcatheter hepatic arterial embolization on coagulation and fibrinolysis in patients with hepatocellular carcinoma. 166 Feb 19

Patients with unstable angina pectoris (UAP; n = 20) and acute myocardial infarction (AMI; n = 34) were studied in the acute phase of ischaemic heart disease. We found significantly higher levels of thrombin-antithrombin-III (TAT) complexes, lower levels of systemic tissue plasminogen activator (t-PA) activity, and higher levels of plasminogen activator inhibitor (PAI) activity in the AMI patients compared to the UAP patients. In contrast to these specific changes, general acute phase reactants such as C-reactive protein, fibrinogen and von Willebrand factor did not differ significantly between the two groups. Studies of the relationship between coagulation (TAT-complexes) and fibrinolysis data revealed a significant positive correlation between plasma antigen concentrations of TAT-complexes and t-PA (P less than 0.02), and between TAT-complexes and PAI-I (P less than 0.002). These observations indicate a common pathophysiological mechanism underlying the changes in coagulation and fibrinolysis, suggesting that coagulation activity and t-PA-related fibrinolysis are interrelated processes in vivo, and probably take place at the level of the endothelial cell.
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PMID:Interrelationship between coagulant activity and tissue-type plasminogen activator (t-PA) system in acute ischaemic heart disease. Possible role of the endothelium. 170 58

The present study addresses the potential effects of pacing-induced myocardial ischemia on the secretion of coagulant and fibrinolytic factors within the coronary circulation. In 6 patients undergoing programmed ventricular stimulation with repeated induction of clinical ventricular tachycardia, the coronary release of tissue-type plasminogen activator (t-PA) antigen, plasminogen activator inhibitor (PAI) capacity, von Willebrand factor antigen (WF:Ag), and prostacyclin (6-keto-PGF 1a) was measured. Blood samples were collected simultaneously from the ascending aorta and the coronary sinus at baseline and immediately after the induction of ventricular tachycardia. The occurrence of pacing-induced myocardial ischemia was established by myocardial net lactate production. Myocardial ischemia was induced in every patient by repeated pacing trials. Pacing-induced ischemia did not affect the coronary release of any of the above factors. Consequently, there was no alteration of transcardiac gradients of thrombin-antithrombin complexes and D-dimer. The present results indicate that pacing-induced myocardial ischemia does not affect the release of coagulant and fibrinolytic endothelial factors or prostacyclin into the coronary circulation.
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PMID:Pacing-induced myocardial ischemia does not affect the endothelial release of coagulant and fibrinolytic factors into the coronary circulation. 170 56

The interaction between guanidine-activated bovine type 1 plasminogen activator inhibitor (PAI-1) and bovine vitronectin was investigated. Activated PAI-1 bound to vitronectin in a dose- and time-dependent manner, and binding was saturable. The dissociation constant (Kd) for this interaction was estimated to be 3.10(-10) mol/l by Scatchard analysis. Complexes of activated PAI-1 and vitronectin were relatively stable at 4 degrees C (T1/2 greater than 24 h), but dissociated with a T1/2 of 4 h at 37 degrees C. The half-life of PAI-1 activity was increased from 2.5 to 4.5 h upon binding to immobilized vitronectin. In order to identify the binding domain(s) in vitronectin for activated PAI-1, the ability of PAI-1 to bind to vitronectin fragments was assessed. Vitronectin was cleaved by thrombin in a dose- and time-dependent manner, generating fragments of Mr 60,000, 54,000 and 38,000. The PAI-1 binding domain(s) were not destroyed by this treatment, since the digested vitronectin competed with immobilized vitronectin for PAI-1 binding to the same extent as uncleaved vitronectin. The thrombin digested vitronectin fragments were fractionated by SDS-PAGE and analyzed by PAI-1 ligand binding. The smallest fragment (Mr 38,000) retained PAI-1 binding function, and sequence analysis demonstrated that this fragment contained the NH2-terminus of bovine vitronectin. These results suggest that the high-affinity binding site for activated PAI-1 is located in the NH2-terminal region of the bovine vitronectin molecule.
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PMID:Kinetic analysis of the interaction between type 1 plasminogen activator inhibitor and vitronectin and evidence that the bovine inhibitor binds to a thrombin-derived amino-terminal fragment of bovine vitronectin. 171 Sep 30

Plasminogen activator inhibitor 1 (PAI-1) is the fast-acting inhibitor of both tissue-type and urokinase-type plasminogen activators (t-PA, u-PA) and is an essential regulatory protein of the fibrinolytic system. In the presence of either the protein vitronectin or the glycosaminoglycan heparin, PAI-1 is also an efficient inhibitor of thrombin. To assess whether these cofactors turn PAI-1 into a general protease inhibitor or whether their influence is restricted to thrombin, the second-order association rate constants between PAI-1 and the human plasma proteases t-PA, u-PA, plasmin, thrombin, Factor Xa (FXa), and Factor XIIa (FXIIa) in the absence and in the presence of either vitronectin or heparin are determined. In addition, the role of the PAI-1 reactive site P3 to P3' residues for the specificity of inhibition was studied by using PAI-1 reactive site mutants. Our results show that: (1) Heparin exclusively increases the rate of inhibition of thrombin by PAI-1, whereas in the presence of heparin the rate of inhibition of the other proteases is not altered; (2) Vitronectin is an obligatory cofactor for the inhibition of thrombin by PAI-1. In addition, vitronectin moderately increases the rate of inhibition by PAI-1 of u-PA and of plasmin, but does not alter the rate of inhibition of t-PA, FXa, or FXIIa; (3) Apart from the important role of the P1 residue, no consensus can be presented on the nature of other residues within the P3 to P3' region with regard to target protease specificity.
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PMID:On the target specificity of plasminogen activator inhibitor 1: the role of heparin, vitronectin, and the reactive site. 171 20

Routine postoperative monitoring of plasma coagulation and fibrinolysis system values after cesarean delivery in 191 women who did not develop thrombosis and 16 who did revealed a preoperative defect in the fibrinolysis (PAI, TAT) and inhibitor (AT III) systems. Significant postoperative correlations in the drop in antithrombin levels could not be explained solely by hemodilution. Moreover, a disturbance of the equilibrium of the alpha-2 increase and plasminogen was observed, favouring alpha-2 antiplasmin. Hydroxyethyl starch is capable of simultaneously influencing hypercoagulability and postoperative status. The only difference noted between the two groups of drugs was in the course of the PAI concentration (P less than 0.02). It would therefore appear logical in clinical practice to extend preoperative tests to include determination of the plasminogen activator inhibitor and the thrombin-antithrombin complex.
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PMID:[Changes in plasma coagulation and fibrinolysis following cesarean section and relationship to deep venous thrombosis. Results of a randomized prospective comparative study with 6% hydroxyethyl starch 0.62 and low-dose heparin as thrombosis prophylaxis]. 171 8

We studied the quantitative changes of hemostatic molecular markers with time during the course of disseminated intravascular coagulation (DIC) induced by endoscopic embolization using thrombin for esophageal varices in nine patients with liver cirrhosis. The plasma levels of D-dimer, a product of plasmin degradation of cross-linked fibrin, and thrombin-antithrombin-III complex (TAT) were significantly higher in patients before treatment when compared with 60 healthy individuals. The plasma levels of TAT, D-dimer, and plasmin alpha 2-plasmin inhibitor complex (PIC) increased significantly 5-15 min after thrombin injection into the varices, earlier than the changes of conventional coagulofibrinolytic factors, reached a maximum level after 180 min, and started to decline after 1 day. Although the plasma PIC level returned to normal after 7 days, both TAT and D-dimer were still above the pretreatment level. Although there was no change in urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA) increased significantly after 5 min. The plasma level of plasminogen activator inhibitor type 1 (PAI-1) showed only a slight elevation after treatment. We propose that the hemostatic molecular markers TAT, D-dimer, and PIC are suitable for the early diagnosis of DIC after endoscopic embolization using thrombin in patients with liver cirrhosis and that the increase of PAI-1 is too small for the regulation of fibrinolysis due to t-PA in DIC occurring in liver cirrhosis.
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PMID:Significance of hemostatic molecular markers during disseminated intravascular coagulation in patients with liver cirrhosis treated by endoscopic embolization for esophageal varices. 171 8

Vitronectin endows plasminogen activator inhibitor 1 (PAI-1), the fast-acting inhibitor of both tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), with additional thrombin inhibitory properties. In view of the apparent association between PAI-1 and vitronectin in the endothelial cell matrix (ECM), we analyzed the interaction between PAI-1 and thrombin in this environment. Upon incubating 125I-labeled alpha-thrombin with endothelial cell matrix (ECM), the protease formed SDS-stable complexes exclusively with PAI-1, with subsequent release of these complexes into the supernatant. Vitronectin was required as a cofactor for the association between PAI-1 and thrombin in ECM. Metabolic labeling of endothelial cell proteins, followed by incubation of ECM with t-PA, u-PA, or thrombin, indicated that all three proteases depleted PAI-1 from ECM by complex formation and proteolytic cleavage. Proteolytically inactive thrombin as well as anticoagulant thrombin, i.e., thrombin in complex with its endothelial cell surface receptor thrombomodulin, did not neutralize PAI-1, emphasizing that the procoagulant moiety of thrombin is required for a functional interaction with PAI-1. A physiological implication of our findings may be related to the mutual neutralization of both PAI-1 and thrombin, providing a new link between plasminogen activation and the coagulation system. Evidence is provided that in ECM, procoagulant thrombin may promote plasminogen activator activity by inactivating PAI-1.
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PMID:Thrombin neutralizes plasminogen activator inhibitor 1 (PAI-1) that is complexed with vitronectin in the endothelial cell matrix. 172 12

Two important haematological problems were found in an otherwise healthy 78 year old man: chronic myelomonocytic leukaemia; and a complex, acquired, hyperfibrinolytic bleeding disorder characterized by prolonged coagulation times, deficiency of coagulation factors V, X, and XI, anti-thrombin III and proteins C and S, with high concentrations of circulating tissue plasminogen activator, and low concentrations of plasminogen activator inhibitor. There may be a causal relation between the two conditions, with the peripheral blood monocytes mediating the hyperfibrinolytic process by the abnormal production of tissue plasminogen activator, though no previous description of a similar association has been reported.
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PMID:Bleeding diathesis coincident with chronic myelomonocytic leukaemia. 175 89


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