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

The relationship of N-linked glycosylation and association with heavy chain binding protein (BiP) to the secretion of Factor VIII (FVIII), von Willebrand Factor (vWF), and tissue plasminogen activator (tPA) was studied in Chinese hamster ovary (CHO) cells. FVIII has a heavily glycosylated region containing 20 clustered potential N-linked glycosylation sites. A significant proportion of FVIII was detected in a stable complex with BiP and not secreted. Deletion of the heavily glycosylated region resulted in reduced association with BiP and more efficient secretion. Tunicamycin treatment of cells producing this deleted form of FVIII resulted in stable association of unglycosylated FVIII with BiP and inhibition of efficient secretion. vWF contains 17 potential N-linked glycosylation sites scattered throughout the molecule. vWF was transiently associated with BiP and efficiently secreted demonstrating that CHO cells are competent to secrete a highly glycosylated protein. tPA, which has three utilized N-linked glycosylation sites, exhibited low level association with BiP and was efficiently secreted. Disruption of N-linked glycosylation of tPA by either site-directed mutagenesis or tunicamycin treatment resulted in reduced levels of secretion and increased association with BiP. This effect was enhanced by high levels of tPA expression. The glycosylation state and extent of association with BiP could be correlated with secretion efficiency.
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PMID:The relationship of N-linked glycosylation and heavy chain-binding protein association with the secretion of glycoproteins. 312 36

The fibrinolytic system comprises a proenzyme, plasminogen, which can be converted to the active enzyme plasmin, which will degrade fibrin. Plasminogen activation is mediated by plasminogen activators which are classified as either tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA). Inhibition of the fibrinolytic system may occur at the level of the activators or at the level of generated plasmin. Plasmin has a low substrate specificity and when circulating freely in the blood will degrade several proteins including fibrinogen, Factor V and Factor VIII. Plasma does, however, contain a fast-acting plasmin inhibitor, alpha 2-antiplasmin, which will inhibit free plasmin extremely rapidly (t1/2: 0.1 s) but which reacts much slower (10(3)-fold) with plasmin bound to fibrin. A "systemic fibrinolytic state" may, however, occur by extensive activation of plasminogen (conc. in plasma 2 microM) and depletion of alpha 2-antiplasmin (conc. in plasma 1 microM). Clot-specific thrombolysis therefore requires plasminogen activation restricted to the vicinity of the fibrin. Two physiological plasminogen activators, t-PA and single-chain u-PA (scu-PA) induce clot-specific thrombolysis, however via entirely different mechanisms. t-PA is relatively inactive in the absence of fibrin, but fibrin strikingly enhances the activation rate of plasminogen by t-PA. This is explained by an increased affinity of fibrin-bound t-PA for plasminogen and not by alteration of the catalytic rate constant of the enzyme. The high affinity of t-PA for plasminogen in the presence of fibrin thus allows efficient activation on the fibrin clot while no significant plasminogen activation by t-PA occurs in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Fibrin-specific thrombolytic agents. 312 44

Ternary complex formation of tissue plasminogen activator (TPA) and plasminogen (Plg) with thrombospondin (TSP) or histidine-rich glycoprotein (HRGP) has been demonstrated using an enzyme-linked immunosorbent assay, an affinity bead assay, and a rocket immunoelectrophoresis assay. The formation of these complexes was specific, concentration dependent, saturable, lysine binding site-dependent, and inhibitable by fluid phase plasminogen. Apparent Kd values were approximately 12-36 nM for the interaction of TPA with TSP-Plg complexes and 15-31 nM with HRGP-Plg complexes. At saturation the relative molar stoichiometry of Plg:TPA was 3:1 within the TSP-containing complexes and 1:1 within HRGP-containing complexes. The activation of Plg to plasmin by TPA on TSP- and HRGP-coated surfaces was studied using a synthetic fluorometric plasmin substrate (D-Val-Leu-Lys-7-amino-4-trifluoromethyl coumarin). Kinetic analysis demonstrated a marked increase in the affinity of TPA for plasminogen in the presence of surface-associated TSP or HRGP. Compared to fluid phase activation or activation on fibronectin- or Factor VIII-related antigen-coated surfaces there was a 35-fold increase in efficiency of plasmin generation. A substantial amount (up to 71%) of the plasmin formed remained surface-associated and was found to be protected from inhibition by alpha 2-plasmin inhibitor. Greater than 200-fold increase in inhibitor concentration was required to effect 50% inhibition. Complex formation of locally released tissue plasminogen activator with Plg immobilized on TSP or HRGP surfaces may thus play an important role in effecting proteolytic events in nonfibrin-containing microenvironments.
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PMID:Activation of immobilized plasminogen by tissue activator. Multimolecular complex formation. 316 Jul 7

Blood coagulation and fibrinolysis variables have been studied in the normal puerperium in order to facilitate the decision to discontinue thrombosis prophylaxis after delivery. 16 women were followed longitudinally from the 1st to the 6th week post partum. Factor VIII activity and related antigen, fibrinogen, fibrinopeptide A, antithrombin III, plasminogen, tissue plasminogen activator (t-PA), fast inhibitor of t-PA, alpha 2-antiplasmin, urokinase inhibitors, fragment B beta 15-42 and kallikrein inhibition were analyzed. Both blood coagulation and fibrinolysis were significantly increased during the first 2 weeks, although simultaneously increased inhibitor capacity of both systems was present. 3 weeks post partum, blood coagulation and fibrinolysis were generally normalized, although the inhibitors remained raised compared to nonpregnant controls throughout the observation period.
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PMID:Changes in blood coagulation and fibrinolysis in the normal puerperium. 393 Mar 49

In nine patients with non-malignant diseases undergoing major upper abdominal surgery, the mechanism of the postoperative fibrinolytic shut-down was investigated because of its potential significance for postoperative deep vein thrombosis by employing new and specific methods for assessing and stimulating the fibrinolytic system. The shut-down was found to result from an impairment of the balance between tissue-type plasminogen activator, t-PA, and its recently discovered fast-acting inhibitor. In this balance, the t-PA antigen concentrations both in resting conditions and after stimulation evoked by desamino-D-arginine vasopressin (DDAVP) were found to be unchanged by surgery. However, there was a significant postoperative increase in t-PA inhibitor levels. The release of t-PA under the stimulus of DDAVP infusion overcame the postoperative shut-down of t-PA activity. However, DDAVP infusion was associated with potentially unfavourable increases in the Factor VIII/von Willebrand factor complex. The discovery of increased t-PA inhibitor in the postoperative period opens new possibilities for a rational approach to reduce or abolish the postoperative fibrinolytic shut-down.
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PMID:Fibrinolytic shut-down after surgery: impairment of the balance between tissue-type plasminogen activator and its specific inhibitor. 393

Vascular or tissue-type plasminogen activator (TPA) is a key enzyme in physiologic fibrinolysis. To study the role of prostaglandins in modulating the synthesis and release of TPA in vivo, we prospectively studied the effect of aspirin (650 mg/d X 2) on TPA activity in 13 human subjects before and after 10 min of forearm venous occlusion. TPA activity was quantified by a newly developed enzyme-linked immunosorbent assay that both measures and differentiates between TPA and urokinase (UK)-like plasminogen activator activity. This assay is based on the observation that the concentration of alpha 2-plasmin inhibitor-plasmin complexes in Reptilase-clotted plasma increases linearly in proportion to the amount of activator added. Resting TPA activity was higher in women than in men (0.56 +/- 0.59 vs. 0.15 +/- 0.11 U/ml, P = 0.049). Venous occlusion induced an eightfold rise in TPA activity in women (to 4.5 U/ml, P = 0.006) and a 15-fold rise in men (to 2.28 U/ml, P = 0.004), whereas UK activity was not detected. Aspirin inhibited the rise in TPA activity after venous occlusion by 69% in men (P = 0.004) and 70% in women (P = 0.014). In contrast, aspirin had no effect on pre- or post-occlusion hematocrits or Factor VIII-related antigen levels. There was no correlation between plasma salicylate level and percentage inhibition of TPA. Neither exogenous aspirin (0-1 microgram/ml) nor salicylate (0-70 micrograms/ml) inhibited the generation of alpha 2-plasmin inhibitor-plasmin complexes by exogenous TPA or interfered with the assay system. We conclude that aspirin may have an antifibrinolytic effect in man that has not been previously described.
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PMID:Aspirin inhibits vascular plasminogen activator activity in vivo. Studies utilizing a new assay to quantify plasminogen activator activity. 623 45

Cuticle bleeding time (CBT) measurements in anesthetized rabbits were performed to assess the potential bleeding risks which may accompany the administration of tissue-type plasminogen activator (tPA) or vampire bat salivary plasminogen activator (BatPA). The dose of BatPA or tPA used in this study, 42 nmol/kg, was previously shown to be efficacious using a rabbit femoral artery thrombosis model (Gardell et al, Circulation 84:244, 1991). CBT was determined by severing the apex of the nail cuticle and monitoring the time to cessation of blood flow. CBT was minimally elevated (1.6-fold, p = NS) following bolus intravenous administration of BatPA; in contrast, bolus intravenous administration of tPA dramatically elevated CBT (6.2-fold, p < 0.05). Rabbits treated with tPA, but not BatPA, displayed profound activation of systemic plasminogen and consequent degradation of Factor VIII and fibrinogen. Elevations in CBT after the administration of tPA were reversed by the replenishment of plasma Factor VIII activity to 40% of control, but were unaffected by complete replenishment of plasma fibrinogen. The results of this study suggest that the administration of BatPA, at a dose that promotes thrombolysis, may evoke a minimal bleeding risk, relative to an equi-efficacious dose of tPA. In addition, the tPA-provoked proteolytic consumption of Factor VIII may be a key contributor to the heightened bleeding risk.
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PMID:Vampire bat salivary plasminogen activator evokes minimal bleeding relative to tissue-type plasminogen activator as assessed by a rabbit cuticle bleeding time model. 754 21

Changes in hemostatic factors after bone marrow transplantation (BMT), with or without thrombotic complications, have already been described. The endothelium seems to be actively involved in such processes. Over a period of 2 years we evaluated various hemostatic factors, associated or not with endothelial stimulation, in 44 patients with BMT (40 leukemias and 4 aplastic anemias). Factor VIII activity (VIII:C), von Willebrand factor antigen (vWF:Ag), tissue plasminogen activator antigen (tPA), plasminogen activator inhibitor activity (PAI-1), antithrombin III, protein C and protein S were assayed before and 1, 3, 6, 12, 18, and 24 months after BMT. Factor VIII:C, vWF and tPA were found to be significantly increased 1-6 months after BMT, returning to normal later. Patients with acute graft versus host disease, fever or cyclosporin treatment had significantly higher VIII:C, vWF and tPA. The increase in these factors implies lasting stimulation of their release and/or synthesis from endothelial cells that is enhanced by some complications of BMT. The degree and character of these changes could favor activation of thrombotic processes.
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PMID:[Activation of endothelium-dependent hemostatic factors following bone marrow transplantation]. 789 69

The effect of different fat loads on postprandial lipemia and hemostatic activity was examined in 10 middle-aged men using 3 different meals. One meal was rich in saturated fatty acids (cream), the other rich in n-6 polyunsaturated fatty acids (sunflower oil) and the third was fat-free containing only carbohydrates. Lipoprotein lipids and hemostatic parameters were measured during fasting and 2, 4, 6 and 8 h after the test meal. In fasting samples, several hemostatic parameters were significantly associated with lipoprotein lipids. Most notable were the strong associations of fibrinolysis parameters tissue plasminogen activator antigen and plasminogen activator inhibitor activity (PAI-1) with total and very low density lipoprotein (VLDL) triglycerides. During lipemia, the associations were approximately similar or slightly weaker than in the fasting state. Both fat loads resulted in similar postprandial lipid responses: VLDL and high density lipoprotein (HDL) triglycerides reached maximum at 4 h after the meal. VLDL cholesterol also increased 4 and 6 h after the fat loads. HDL3 cholesterol declined after the fatty meals but no change was observed in the HDL2 fraction. The fat-free meal gave no significant lipid changes during the time course studied. Factor VII activity (F VII:C) increased 6 and 8 h after the fatty meals, whereas a decrease was observed after the fat-free meal. The changes (+/- S.D.) at 8 h after cream, sunflower oil and fat-free meal were 5.2 +/- 3.3, 3.3 +/- 4.2 and -5.8 +/- 7.9 percentage points, respectively, and the effect of the meal on the changes was statistically significant (F (8,99) = 2.99, P = 0.0048). F VII antigen (F VII:Ag) tended to decline during the day but there was no difference between the meals. Factor VIII activity (F VIII:C) was highest after the polyunsaturated fat meal and lowest after the fat-free meal. PAI-1 declined during the day and the decline tended to be steepest after the fat-free morning meal. The effect of the meal on the changes in lipoprotein lipids and hemostatic factors varied significantly between individuals. In conclusion, postprandial lipemia after a single fatty meal was associated with procoagulatory change in F VII:C but there was no difference between saturated fat and n-6 polyunsaturated fat.
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PMID:The effects of saturated fat and n-6 polyunsaturated fat on postprandial lipemia and hemostatic activity. 828 Jan 80

Vasopressin and in particular its structural analogue dDAVP (1-deamino-8-D-arginine vasopressin) can increase plasma concentrations of Factor VIII and tissue plasminogen activator (tPA) in some species of animals and in humans. For this reason dDAVP is used therapeutically in the treatment of bleeding episodes in patients suffering from haemophilia A and Von Willebrand's disease. However, the high antidiuretic activity of dDAVP constitutes and unwanted effect in this context. In the present study, a large number of analogues of vasopressin were designed, synthesized and tested in monkeys with the aim of producing compounds in which the Factor VIII-releasing activity was selectively isolated from the vasopressor and antidiuretic actions of the peptide. The results indicate that it is possible to separate these biological activities; however, none of the analogues tested so far possessed Factor VIII potencies comparable to that of dDAVP.
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PMID:Antidiuretic activity and release of factor VIII by vasopressin analogues. 846 59


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