Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.6 (thromboplastin)
 13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The three-dimensional structure of a thrombin inhibitor-trypsin complex has been determined by an X-ray analysis at 2.5 A resolution. The result has given experimental support to the mechanisms previously proposed by the authors for the selective inhibition of trypsin, thrombin, factor Xa, and plasmin by inhibitors with an arginine or lysine backbone. The differences in the amino acid sequences at the positions corresponding to Ilc63, Leu99, and Ser190 of trypsin give each enzyme different binding affinities toward inhibitors and result in the selective inhibition. Furthermore, the X-ray analysis has revealed a novel type of interaction between the inhibitor and trypsin. The hydrogen bonds between the inhibitor main chain and trypsin Gly216 play an essential role in the complex formation.
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PMID:X-ray analysis of a thrombin inhibitor-trypsin complex. 276 21

Blood from adult male Wistar rats clotted rapidly in glass or siliconized tubes; the clots retracted and did not lyse. The serum prothrombin, plasma prothrombin and activated partial thromboplastin times were shorter than those of normal humans. In contrast, the thrombin and reptilase times were longer than those of normal human plasma, due apparently to the presence of a low-grade thrombin inhibitor in rat plasma. Coagulation factors, X, VIIIR:vW and IX assayed lower in rat than human plasma, while factors VIII:C and anti-thrombin III were higher. Values for other coagulation factors (II, V, VII, XI, XII and Fletcher) fell within the human range. Platelets were small and numerous. They aggregated well with ADP but poorly or not at all with collagen, ristocetin, thrombin, epinephrine, arachidonic acid and pig or bovine plasmas. Leukocytes numbered 4-8 X 10(3) cells/mm3, a near human range and were predominantly lymphocytic. Erythrocytes were small (MCV = 56-60 fl) and numerous (5.5-6.4 X 10(6) cells/mm3).
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PMID:Comparative hematology and coagulation: studies on rodentia (rats). 286 3

The tertiary structure of a thrombin inhibitor-trypsin complex has been predicted by a molecular modelling considering the van der Waals interactions between the inhibitor and the enzyme. The selective inhibition of trypsin, thrombin, factor Xa, and plasmin exhibited by arginine and lysine derivatives has been clearly explained based on the predicted structure and the homology in the amino acid sequences of these enzymes. The differences in the amino acid sequences at the positions corresponding to Ile63, Leu99, and Ser190 of trypsin give each enzyme different binding affinities toward inhibitors and result in the selective inhibition. The X-ray analysis of the inhibitor-trypsin complex is in progress to prove the predicted structure.
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PMID:A predicted tertiary structure of a thrombin inhibitor-trypsin complex explains the mechanisms of the selective inhibition of thrombin, factor Xa, plasmin, and trypsin. 296 79

We examined the effect of a synthetic thrombin inhibitor, MCI-9038, on two experimental animal models of disseminated intravascular coagulation (DIC). In a model that DIC induced by the intravenous infusion of thrombin, MCI-9038 suppressed the decrease of platelet count by about 50% at a dose of 0.2 micrograms/kg/min and almost completely at 2 micrograms/kg/min. When MCI-9038 was administered orally, the suppressive effect was also observed. Heparin suppressed the platelet count decrease by about 50% at 1 unit/kg/min. In another model of DIC induced by lactic acid and tissue thromboplastin infusion, MCI-9038 prevented the decrease of platelet count and the consumption of coagulation factors. The suppression effect by about 50% on these changes was observed at a dose of 3.16 micrograms/kg/min. Thromboelastogram pattern indicating the consumption coagulopathy in control experiments was normalized by the MCI-9038 administration. Heparin suppressed the decrease of fibrinogen content as effectively as MCI-9038, but it was less effective on the platelet count decrease. From these results, it was concluded that MCI-9038 might be useful for the treatment of DIC.
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PMID:Effect of a synthetic thrombin inhibitor MCI-9038 on experimental models of disseminated intravascular coagulation in rabbits. 360 10

This study reports on the anticoagulant, antithrombotic and bleeding effects of a new synthetic direct thrombin inhibitor (SDTI) in comparison with standard heparin (SH). The anticoagulant effect was determined with the thrombin clotting time (TCT) and the activated partial thromboplastin time (APTT). SDTI was more potent than SH in prolonging the TCT, but as potent as SH in prolonging the APTT. The antithrombotic effect was determined using a modified Wessler model in the rabbit, either 30 min after a continuous IV infusion of increasing doses or at various times after a single SC injection (20 mg/kg). After continuous IV infusion of 187 micrograms/kg/h of SDTI and of 60 micrograms/kg/h of SH, significant thrombus prevention effects were obtained (59 and 57% respectively). Increasing the dose of SDTI up to 3000 micrograms/kg/h did not significantly improve the antithrombotic effect. After SC injection, a significant antithrombotic effect was observed for 12 h with SDTI but for more than 24 h with SH. The bleeding effect was studied using the rabbit ear model 15 min after a continuous infusion of 7.5 and 15 mg/kg/h: the amounts of blood loss were dose-dependent and comparable for SDTI and SH. These studies also indicated that SDTI possesses a considerable shorter half-life in comparison with SH. Accordingly, the ex vivo concentrations generated after continuous IV infusion or SC injection of the same dose were higher for SH than for the SDTI.
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PMID:Antithrombotic and bleeding effects of a new synthetic direct thrombin inhibitor and of standard heparin in the rabbit. 367 29

The activation of bovine prothrombin by prothrombinase (Factor Xa, Factor Va, synthetic phospholipid vesicles, and calcium ion) was studied in the presence of the fluorescent, reversible thrombin inhibitor dansylarginine-N-(3-ethyl-1,5-pentanediyl) amide (DAPA). Recordings of fluorescence intensity during prothrombin activation exhibited maxima that decreased to stable limiting values. These data suggested the transient appearance of the meizothrombin-DAPA complex, which exhibits fluorescence with 1.5-fold greater intensity than the thrombin-DAPA complex. At substrate concentrations well below Km, progress curves could be fitted by equations describing an ordered, sequential conversion of prothrombin to thrombin through the intermediate meizothrombin via two pseudo-first order steps. The pseudo-first order rate constants for both steps varied linearly with enzyme concentration, indicating that both steps are catalyzed by prothrombinase. The progress of the reaction was also monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometry analyses of aliquots removed at intervals spanning the reaction. These analyses confirmed both the existence of meizothrombin and its time course as predicted from the equations used to analyze fluorescence intensity profiles. Meizothrombin levels peaked at about 0.3 mol/mol initial prothrombin under the conditions typically studied. In addition, prethrombin 2, which is the intermediate expected from cleavages occurring in the order opposite that required to form meizothrombin, was not observed under any of the conditions examined. These data indicate that prothrombin activation catalyzed by the fully assembled prothrombinase complex proceeds via an ordered, sequential reaction with meizothrombin as the sole intermediate.
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PMID:The prothrombinase-catalyzed activation of prothrombin proceeds through the intermediate meizothrombin in an ordered, sequential reaction. 375 35

The kinetics of the activation of human prothrombin catalyzed by human prothrombinase was studied using the fluorescent alpha-thrombin inhibitor dansylarginine-N-(3-ethyl-1,5-pentanediyl)amide (DAPA). Prothrombinase proteolytically activates prothrombin to alpha-thrombin by cleavages at Arg273-Thr274 (bond A) and Arg322-Ile323 (bond B). The differential fluorescence properties of DAPA complexed with the intermediates and products of human prothrombin activation were exploited to study the kinetics of the individual bond cleavages in the zymogen. When the catalyst was composed of prothrombinase (human factor Xa, human factor Va, synthetic phospholipid vesicles, and calcium ion), initial velocity studies of alpha-thrombin formation indicated that the kinetic constants for the cleavage of bonds A or B were similar to the constants that were obtained for the overall reaction (bonds A + B). The progress of the reaction was also monitored by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The results indicated that the activation of human prothrombin catalyzed by prothrombinase proceeded exclusively via the formation of meizothrombin (bond B-cleaved) as an intermediate. Kinetic studies of the cofactor dependence of the rates of cleavage of the individual bonds indicated that, in the absence of the cofactor, cleavage at bond B would constitute the rate-limiting step in prothrombin activation. Progress curves for prothrombin activation catalyzed by prothrombinase and monitored using the fluorophore DAPA were typified by the appearance of a transient maximum, indicating the formation of meizothrombin as an intermediate. When factor Xa alone was the catalyst, progress curves were characterized by an initial burst phase, suggesting the rapid production of prethrombin 2 (bond A-cleaved) followed by its slow conversion to alpha-thrombin. Gel electrophoresis followed by autoradiography was used to confirm these results. Collectively, the results indicate that the activation of human prothrombin via the formation of meizothrombin as an intermediate is a consequence of the association of the cofactor, human factor Va, with the enzyme, human factor Xa, on the phospholipid surface.
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PMID:Activation of human prothrombin by human prothrombinase. Influence of factor Va on the reaction mechanism. 381 42

Prothrombinase affects the proteolytic conversion of prothrombin to thrombin and is the penultimate enzyme in the common coagulation pathway. Prothrombinase is a complex in which the proteinase, Factor Xa, a cofactor, Factor Va, and calcium are bound to a membrane surface to generate the active enzyme. Guinea pig line 1 and line 10 tumor cells, grown as primary cultures from ascites tumors or as cell lines in culture, provide a surface that interacts with coagulation Factor Va and Xa and with calcium ions to form this enzyme complex. Cultured human colorectal carcinoma cells (Colo 205) also participate in prothrombinase complex assembly and function. Prothrombinase generation was measured by following the kinetics of prothrombin conversion to thrombin. Thrombin generation was monitored continuously using the reversible thrombin inhibitor, dansylarginine N-(3-ethyl-1,5-pentanediyl)amide, which displays enhanced fluorescence upon binding to thrombin. Analyses of kinetic data indicate that the apparent dissociation constants (1-4 X 10(-10) mol/liter) and the number of Factor Va-Xa binding sites per tumor cell are comparable to values reported for human and bovine platelets, human lymphocytes, and monocytes. Guinea pig lymphocytes were also active, while erythrocytes were inactive, in the prothrombinase assay. Membrane vesicles, shed by guinea pig and human tumor cells into conditioned medium, also supported functional prothrombinase activity. Although earlier studies indicated that tumor cells may initiate coagulation, this is the first demonstration that tumor cells are competent to bring clotting to fruition by generating thrombin, a step essential to fibrin generation. These data suggest that tumor cells, in the presence of clotting initiators and appropriate coagulation factors, are sufficient to generate the fibrin deposited in solid tumors.
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PMID:Tumor cell generation of thrombin via functional prothrombinase assembly. 405 25

A synthetic thrombin inhibitor, MD-805, was used to anticoagulate 15 patients after cardiovascular surgery (CVS). A mean infusion rate of 0.71 +/- 0.1 (SD) microgram/kg . min maintained an activated coagulation time of about 150 sec in all patients, and significantly prolonged both activated partial thromboplastin time and prothrombin time. MD-805 was also administered to ten patients with disseminated intravascular coagulation (DIC), eight of whom had not responded to either heparin or gabexate mesilate (FOY), and eight of whom had circulating antithrombin III levels below 20 mg/dl. MD-805 therapy was successful in nine DIC patients. These results recommend MD-805 anticoagulant therapy after CVS and for treatment of DIC, especially when circulating levels of antithrombin III are low.
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PMID:Anticoagulation with a synthetic thrombin inhibitor after cardiovascular surgery and for treatment of disseminated intravascular coagulation. 643 71

Immunization of goats and mules with human thrombin resulted in an antiserum that reacted only weakly with the parent molecule, prothrombin. Some of the antibodies in this antiserum showed a greater affinity for thrombin complexed to its naturally occurring inhibitor, antithrombin-III, than for active thrombin. An antiserum against the human thrombin inhibitor, antithrombin-III, produced 2 precipitin lines against human serum but only 1 against plasma. The 2nd line in serum was shown to represent precipitation of a complex of thrombin with antithrombin-III. The neoantigens appearing in antithrombin-III after complex formation were also present in complexes prepared with purified clotting factor Xa and antithrombin-III. Since purified host (mule) thrombin was also capable of causing formation of the neoantigenic sites when complexed to human antithrombin-III, it seems likely that these determinants result from interaction in the host between the immunogens (either human thrombin or antithrombin) and the appropriate interacting host protein (mule antithrombin-III or thrombin, respectively). Studies by radioimmunoassay showed that the antibodies formed are not completely specific for the neoantigens since they also react to a lesser extent with the free proteins.
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PMID:Antigenic changes produced by complex formation between thrombin and antithrombin-III. 678 23


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