Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.68 (tissue plasminogen activator)
 11,311 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have generated site-specific mutants of the kringle 2 domain of tissue-type plasminogen activator [( K2tPA]) in order to identify directly the cationic center of the protein that is responsible for its interaction with the carboxyl group of important omega-amino acid effector molecules, such as epsilon-amino caproic acid (EACA). Molecular modeling of [K2tPA], docked with EACA, based on crystal structures of the kringle 2 region of prothrombin and the kringle 4 domain of human plasminogen, clearly shows that Lys33 is the only positively charged amino acid in [K2tPA] that is sufficiently proximal to the carboxyl group of the ligand to stabilize this interaction. In order to examine directly the importance of this particular amino acid residue in this interaction, we have constructed, expressed, and purified three recombinant (r) mutants of [K2tPA], viz., Lys33Thr, Lys33Leu, and Lys33Arg, and found that only the last variant retained significant ability to interact with EACA and several of its structural analogues at neutral pH. In addition, another mutated r-[K2tPA], i.e., Lys33His, interacts very weakly with omega-amino acids at neutral pH and much more strongly at lower pH values where His33 would be expected to undergo protonation. This demonstrates that any positively charged amino acid at position 33 satisfies the requirement for mediation of significant bindings to this class of molecules. Since, in other kringles, positively charged residues at amino acid sequence positions homologous to Lys68, Arg70, and Arg71 of [K2tPA] have been found to participate in kringle interactions with EACA-like compounds, we have also examined the binding of EACA, and some of its analogues, to three additional r-[K2tPA] variants, i.e., Lys68Ala, Arg70Ala, and Arg71Ala. In each case, binding of these omega-amino acids to the variant kringles was observed, with only the Lys68Ala variant showing a slightly diminished capacity for this interaction. These investigations provide clear and direct evidence that Lys33 is the principal cationic site in wild-type r-[K2tPA] that directly interacts with the carboxyl group of omega-amino acid effector molecules.
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PMID:Direct identification of lysine-33 as the principal cationic center of the omega-amino acid binding site of the recombinant kringle 2 domain of tissue-type plasminogen activator. 130 92

The crystal structure of the kringle 2 domain of tissue plasminogen activator was determined and refined at a resolution of 2.43 A. The overall fold of the molecule is similar to that of prothrombin kringle 1 and plasminogen kringle 4; however, there are differences in the lysine binding pocket, and two looping regions, which include insertions in kringle 2, take on very different conformations. Based on a comparison of the overall structural homology between kringle 2 and kringle 4, a new sequence alignment for kringle domains is proposed that results in a division of kringle domains into two groups, consistent with their proposed evolutionary relation. The crystal structure shows a strong interaction between a lysine residue of one molecule and the lysine/fibrin binding pocket of a noncrystallographically related neighbor. This interaction represents a good model of a bound protein ligand and is the first such ligand that has been observed in a kringle binding pocket. The structure shows an intricate network of interactions both among the binding pocket residues and between binding pocket residues and the lysine ligand. A lysine side chain is identified as the positively charged group positioned to interact with the carboxylate of lysine and lysine analogue ligands. In addition, a chloride ion is located in the kringle-kringle interface and contributes to the observed interaction between kringle molecules.
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PMID:Crystal structure of the kringle 2 domain of tissue plasminogen activator at 2.4-A resolution. 131 33

The effects of the oral administration of 100 or 200 mg of heparan sulphate or placebo over time were assessed in nine healthy volunteers. Blood samples were collected at 1, 2, 4, 6, 8 and 12 hours after administration to assay prothrombin activity, partially activated thromboplastin time, and the activation to tPA and PAI-1. A significant increase (P < 0.001) of tPA activity and a reduced inhibition of fibrinolytic systems by PAI-1 were observed. These effects, which were clearly dose-dependent, appeared 2 hours after administration and persisted for 6-8 hours. On the contrary, no changes were recorded in coagulative tests at the doses used.
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PMID:[Heparan sulfate: its kinetic effects on fibrinolytic-coagulative parameters after oral administration]. 143 3

A 29-year-old man with congenital protein C deficiency and acute myocardial infarction is reported. Four hours after the onset of chest pain, he was treated intravenously with tissue-type plasminogen activator. Subsequent coronary angiography revealed only slight stenosis of the left anterior descending coronary artery without any atherosclerosis. The propositus, his brother, and his mother, showed low levels of both protein C activity and antigen, while plasma thrombomodulin levels were normal. His grandfather had died from acute myocardial infarction at 38 years of age. We investigated several other risk factors for arterial thrombosis, including factor VII, fibrinogen, heparin cofactor II, lipoprotein (a), and anticardiolipin antibodies. No other haemostatic abnormalities apart from factor VII hyperactivity were detected in this family. To study the effects of protein C and factor VII on procoagulant activity, prothrombin time was measured after the addition of activated protein C and factor VII to protein C-deficient plasma. The prothrombin time ratio decreased along with an increase in the factor VII level. It also decreased with a decrease in the activated protein C level. These findings indicated that the procoagulant activity of factor VII was enhanced by low protein C levels, suggesting that concomitant factor VII hyperactivity may cause acute myocardial infarction in patients with protein C deficiency.
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PMID:Congenital protein C deficiency and myocardial infarction:concomitant factor VII hyperactivity may play a role in the onset of arterial thrombosis. 144 May 17

Increases in thrombin activity in patients given fibrinolytic agents for acute myocardial infarction have been shown to be important in limiting the ultimate success of coronary thrombolysis. The present study was designed to determine whether increases in thrombin activity reflect, in part, activation of prothrombin accompanying thrombolysis. Plasma concentrations of prothrombin fragment 1.2, a polypeptide released when prothrombin is activated by factor Xa, were measured in 22 patients with acute myocardial infarction before and after treatment with 100 mg of recombinant tissue-type plasminogen activator (rt-PA). Concentrations of prothrombin fragment 1.2 increased from 0.83 +/- 1.1 nM (mean +/- SD) before rt-PA infusion to 1.5 +/- 1.5 nM 2 h after initiation of the infusion (p less than 0.05). After a 5,000-U intravenous dose of heparin given at the end of the infusion of rt-PA, concentrations of prothrombin fragment 1.2 decreased from 1.8 +/- 1.5 to 1.1 +/- 0.9 nM (n = 20, p less than 0.05), although values were still increased compared with concentrations before rt-PA. These results indicate that thrombin activity increases in patients given rt-PA at least in part because of activation of the coagulation system leading to activation of prothrombin. Thus, inhibition of the reactions involving coagulant proteins that lead to activation of prothrombin may be of value as conjunctive treatment to potentiate the efficacy of pharmacologic thrombolysis.
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PMID:Activation of prothrombin accompanying thrombolysis with recombinant tissue-type plasminogen activator. 155 97

We retrospectively evaluated the hemostatic system of 13 patients during implantation (2 to 35 days) of the Jarvik 7-70 total artificial heart (TAH). Although all patients were clinically manageable while on the TAH, 5 had excessive generalized bleeding. After the heart transplant procedure, 2 patients had neurological events and 1 patient, thrombosis of the leg. While the patients were supported by the TAH, the routine coagulation assays (prothrombin time, activated partial thromboplastin time, fibrinogen, factor assays, and platelet count) showed slight abnormalities but no correlation to hemorrhagic or thrombotic events. In contrast, plasma and cellular activation markers, which are highly sensitive and specific for hypercoagulability, fibrinolysis, or platelet activation, revealed activation in all patients. Most striking was the marked activation of the fibrinolytic system (p less than 0.05 to 0.001). Correlations of individual patient data compared with the average TAH group response could be made between excessive enhancement of fibrinolysis (increased D-dimer and tissue plasminogen activator and decreased plasminogen activator inhibitor) and bleeding. A hypercoagulable state (increased fibrinogen and thrombin-antithrombin complex and decreased antithrombin III and protein C), decreased fibrinolysis (decreased tissue plasminogen activator and D-dimer), activated platelets (increased thromboxane B2), or combinations of these were associated with thrombosis. The hemostatic activation returned to normal 1 day after removal of the TAH. These data suggest that the patient with a TAH requires more sophisticated laboratory monitoring and individualized treatment for excessive fibrinolysis, hypercoagulable state, or platelet activation to avoid thrombotic and hemorrhagic complications.
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PMID:Hemostatic abnormalities in total artificial heart patients as detected by specific blood markers. 157 Sep 81

The Kringle-1 structure of plasminogen (PGK-1), the Kringle-2 structure of tissue plasminogen activator (PAK-2) and the Kringle structure of prourokinase (UKK) has been modeled on the basis of the three-dimensional structure of Kringle-1 of prothrombin (PTK-1) at 2.8 A resolution. The predicted three-dimensional structure of these Kringles shows that the binding site of PGK-1 is characterized by an apparent dipolar site, the polar parts of which are separated by a hydrophobic region. PAK-2 possesses the anionic center but has not a cationic binding center which might be provided by a guanidinium group from Arg-69 located adjacent to the Arg-71 position. UKK possesses neither the anionic binding center nor the cationic center which are probably the main reason for the poor fibrin specificity of urokinase.
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PMID:The structural basis of the poor fibrin specificity of urokinase(I)--knowledge-based prediction of kringle structures of urokinase and its related proteins. 158 Oct 2

Monitoring coagulation parameters during thrombolytic therapy could be useful for prediction and treatment of haemorrhagic episodes. Technology based on dry reagent chemistry has been developed that allows rapid (less than 10 min) assays on small samples of whole blood. The assay principle is based on the restriction of motion of paramagnetic particles during fibrin polymerization, and subsequent liberation of particle motion during fibrinolysis. This technology was used to monitor prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen levels and fibrinolysis profiles during thrombolytic therapy with tissue plasminogen activator for acute myocardial infarction. The PT and aPTT obtained with the COAG-1 correlated well with conventional assays (r = 0.93 and 0.92 for PT and aPTT, respectively; p = 0.0001). Fibrinogen estimates, obtained by COAG-2 also correlated well with modified Clauss assays (r = 0.86, p = 0.0001). The rapid determination of the aPTT may improve management of adjunctive anticoagulant therapy following thrombolysis. The fibrinolysis profile may be useful during thrombolytic therapy to verify that a lytic state has been achieved, to monitor the lytic state throughout therapy, and to verify that the lytic state normalizes once therapy has been completed.
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PMID:Exploration of rapid bedside monitoring of coagulation and fibrinolysis parameters during thrombolytic therapy. 162 19

The effects of physical training on hemostatic parameters were evaluated in 56 postmyocardial infarction (MI) patients before and after one month of systematic physical training and in 30 control post-MI patients, who did not undergo such training. There were no significant changes in prothrombin time (PT) and alpha 1-antitrypsin (alpha 1AT) at the beginning and end of the study in either group. Levels of fibrinogen, Factor VIII: C (VIII:C) and von Wildebrand antigen (vWf:Ag), and activities of ATIII and plasminogen (Plg) were significantly decreased in the group with physical training (p less than 0.05), while values were unchanged in the control group. Hematocrit, platelet counts, and alpha 2-plasmin inhibitor (alpha 2PI) activities also decreased in the physical training group (p less than 0.05). In contrast, these variables increased in the control group (p less than 0.05). Activated partial thromboplastin time (aPTT) tended to be prolonged in the group with physical training, while it was shortened in the control group. In a subset of 20 patients with physical training, resting levels of plasmin-alpha 2PI complex (PIC), thrombin-antithrombin III complex (TAT), protein-C (P-C:Ag), plasminogen activator inhibitor-1 (PAI-1), VII:C, and P-C activities had significantly decreased after one month of physical training (p less than 0.05), although tissue plasminogen activator activities remained unchanged. Physical training appeared to suppress coagulability as indicated by the decrease in fibrinogen, VIII:C, vWf:Ag, VII:C, and TAT, and prolongation of aPTT. The decrease in plasminogen, t-PA:Ag, alpha 2PI, PAI-1, and PIC after physical training may result from the decreased coagulability. In conclusion, physical training appears to induce a suppression of the coagulation system in patients in the recovery phase of MI.
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PMID:Blood coagulability and fibrinolytic activity before and after physical training during the recovery phase of acute myocardial infarction. 162 56

Disseminated thrombotic processes in the microcirculation are considered to be an important cause of multiple organ failure in septic patients. Fibrinolysis is one endogenous mechanism protecting the circulation from overwhelming thrombosis. Therefore, we looked for alterations of fibrinolytic parameters (tissue plasminogen activator (t-PA), tissue plasminogen activator inhibitor (PAI), D-dimer, euglobulin-clot-lysis-time (ECLT), plasminogen, alpha 2-antiplasmin) and of some coagulation parameters (prothrombin time, fibrinogen, platelets, antithrombin III, protein C, factor XII) in clearly defined septic patients and for the relations of these values to the severity of the disease (APACHE II-score). An increase in D-dimer and t-PA-antigen was registered in all patients, while factor XII and plasminogen were decreased, indicating an activated fibrinolysis. In contrast the systemic fibrinolytic capacity of the blood was strongly inhibited: t-PA-activity was not detectable, PAI-function was elevated, the ECLT was prolonged and alpha 2-antiplasmin was normal. Coagulation was moderately activated: the platelets, antithrombin III and protein C were decreased, the prothrombin time was prolonged and fibrinogen was normal. The changes in t-PA-antigen, PAI-function, factor XII, prothrombin time and antithrombin III were significantly related to the APACHE II-score of the patients. We conclude that the activation of coagulation is accompanied by an activation of fibrinolysis in the microcirculation, but that systemically the increased inhibitors of fibrinolysis (PAI, alpha 2-antiplasmin) induce a decrease of the fibrinolytic capacity of the blood. The severity of the disease determines the extent of the alterations.
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PMID:Activation and inhibition of fibrinolysis in septic patients in an internal intensive care unit. 169 55


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