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:3.4.21.7 (plasmin)
9,023 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Endothelial cells play a critical role in thromboregulation by controlling the assembly of fibrinolytic constituents on the membrane. The assembly system illustrated in FIGURE 6 is characterized by the binding of circulating glu-plasminogen to a membrane receptor (Pathway 1). A membrane-associated protease (possibly plasmin) converts the inactive zymogen into a catalytically more efficient zymogen lys-plasminogen (Pathway 2). T-PA binds to a specific receptor, retains its catalytic activity, and is protected from its natural inhibitor PAI-1. The membrane provides a favorable environment for plasmin generation (Pathway 3) at the vessel surface and contributes to the maintenance of a physiological nonthrombogenic state. The immobilization and surface activation of plasminogen provides an important mechanism for localizing proteolytic activity at the surface of other cells such as macrophages and tumor cells. Lp(a), a plasminogen-like lipoprotein, by competing at the endothelial surface for plasminogen binding down-regulates endothelial cell plasmin generation and may thus promote localized thrombogenesis that over a period of time contributes to progressive atherosclerosis.
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PMID:Endothelial cell fibrinolytic assembly. 190 39

The potential importance of pleural fibrin deposition in the pathogenesis of pleural injury is supported by both clinical and experimental observations. We hypothesized that the local equilibrium between procoagulant and fibrinolytic activities is disrupted to favor fibrin deposition in exudative pleuritis. To test this hypothesis, we characterized procoagulant and fibrinolytic activities in pleural exudates from patients with pneumonia, lung cancer, or empyema and transudates from patients with congestive heart failure. Procoagulant activity was generally increased in exudative processes and was due mainly to tissue factor. All effusions contained antithrombin III and inhibited factor Xa and thrombin, but endogenous prothrombinase or thrombin activities were variably detected. Pleural fluid fibrinolytic activity was increased in congestive heart failure and was due to both tissue plasminogen activator and urokinase. Depressed fibrinolytic activity was found in pleural exudates despite increased concentrations of plasminogen, mainly glu-1-plasminogen, and was due to inhibition of plasminogen activation by plasminogen activator inhibitors 1 and 2 and of plasmin, in part by alpha 2-antiplasmin. Concentrations of PAI-1 in exudative pleural fluids were increased up to 913-fold, compared with normal pooled plasma. Exudative pleural effusions are characterized by increased procoagulant and depressed fibrinolytic activity, favoring fibrin deposition in the pleural space. The balance of these activities is reversed and favors fibrin clearance in congestive heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Abnormalities of pathways of fibrin turnover in the human pleural space. 206 28

Tissue-type plasminogen activator (t-PA) catalyzes the rate-limiting step in the fibrinolytic cascade: conversion of plasminogen to plasmin. Plasma contains several inhibitors of t-PA that limit its activity and prevent systemic activation of plasminogen. The most important of these is endothelial cell plasminogen activator inhibitor (PAI-1), a member of the serine protease inhibitor (serpin) gene family. We have previously demonstrated that mutation of arginine 304 of t-PA to a glutamic acid residue drastically reduces the rate of interaction between the enzyme and its suicide substrate, PAI-1, without affecting the reactivity of the enzyme toward its normal substrate, plasminogen (Madison, E. L., Goldsmith, E. J., Gerard, R.D., Gething, M.J., and Sambrook, J.F. (1989) Nature 339, 721-724). We report here the use of protein modeling to design a compensatory mutation in PAI-1 (glutamic acid 350 to arginine) and create a molecule that rapidly inhibits this "serpin-resistant" variant of t-PA.
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PMID:Restoration of serine protease-inhibitor interaction by protein engineering. 212 70

A rapid and precise turbidimetric clot lysis assay employing a microtitre plate reader and personal computer is described in detail. The use of such widely available instrumentation, the convenience and rapid throughput suggest the assay could be developed as a reference method with which to measure the potency of tissue plasminogen activator (t-PA) in conjunction with the WHO reference preparation. The method has been used to investigate molecular parameters involved in fibrinolysis. Aggregation status of the fibrin does not appear to influence the mechanism of plasminogen activation and clot lysis by plasmin. High ratios of plasminogen to fibrin resulted in a change in clot turbidity and in a change in the lysis profile of turbidity versus time. This is probably the result of plasminogen binding to fibrin and consequent restriction of the access of plasmin to its sites of cleavage in the fibrin. A simple model is proposed, and equations have been derived, for the kinetics of lysis which adequately describe the mechanism and which are confirmed by experimental data. This model results in estimates of the Km and kcat for the activation of plasminogen by t-PA during clot lysis of approximately 150 nM and 0.1 s-1, respectively, in excellent agreement with published values. The assay should therefore prove useful in quantitative evaluations of the molecular phenomena occurring during fibrinolysis. The more rapid activation of lys-plasminogen than glu-plasminogen by t-PA was confirmed. However, evidence was obtained that the lys-form binds more tightly to fibrin by the same factor. This observation suggested that the appropriate substrate in the kinetic model is fibrin-bound plasminogen.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A precise and rapid microtitre plate clot lysis assay: methodology, kinetic modeling and measurement of catalytic constants for plasminogen activation during fibrinolysis. 212 76

Tissue plasminogen activator (t-PA) is homologous to other serine proteases and contains an apparent activation cleavage site at arginine 275. It has been demonstrated that this arginine-275 can be replaced with either glutamic acid (Tate, K. M., Higgins, D. L., Holmes, W. E., Winkler, M. E., Heyneker, H. L., and Vehar, G. A. Biochemistry 26, 338-343, 1987) or glycine (Peterson, L. C., Johannessen, M., Foster, D., Kumar, A., and Mulvihill, E. Biochim. Biophys. Acta 952, 245-254, 1988; Boose, J. A., Kuismanen, E., Gerard, R., Sambrook, J. and Gething, M.-J. Biochemistry 28, 635-643, 1989) so that the product of the plasminogen activation reaction, plasmin, can no longer hydrolyze the one-chain form of t-PA to the two-chain form. These "one-chain" t-PA variants had diminished activity, compared to wild-type t-PA, in the absence of a cofactor, but in the presence of the fibrin(ogen) cofactor the two variants had activity similar to wild-type t-PA. In order to compare the effects of all possible substitutions, t-PA variants with each of the other nineteen amino acids besides arginine at position 275 were produced by site-directed mutagenesis. All were recovered from cell culture supernatants completely in the one-chain form, except for R275 (wild-type) and R275K, which were partially converted to the two-chain form. These latter two species could be completely converted to the two-chain form by plasmin. In addition, these two forms showed significantly more plasminogen activating activity in the absence of a fibrin(ogen) cofactor, compared to the other 18 variants. In the presence of a cofactor, all of the t-PA mutants had plasminogen activating activity equivalent to wild-type t-PA, except for R275C. The R275C t-PA had comparatively less clot lysis and fibrin binding activity as well. Presumably the new cysteine in this variant was involved in a mixed disulfide or caused misfolding of the molecule resulting in decreased activity. The difference in the plasminogen activating activity of one- and two-chain forms of t-PA was investigated by determining the apparent Michaelis constants and the apparent turnover numbers for R275E t-PA, which remains in the one-chain form throughout the assay, and two-chain R275 t-PA. The kinetic constants were measured in both the presence and the absence of plasmin-digested fibrinogen.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The effect of the one-chain to two-chain conversion in tissue plasminogen activator: characterization of mutations at position 275. 213 48

The activation of plasminogen by two novel hybrid enzymes, constructed from the A-chain of plasmin and the B-chains of tissue-type plasminogen activator (t-PA) or urokinase, was compared with the activation by the parent enzymes. Basal kinetic constants for 'Lys-plasminogen' (human plasminogen with N-terminal lysine) and 'Glu-plasminogen' (human plasminogen with N-terminal glutamic acid) activation were similar to those of the parent activators. The Km for plasminogen turnover for both hybrid enzymes was considerably decreased in the presence of both soluble fibrin and a mimic, a CNBr digest of fibrinogen. These enhancements and the related apparent negative co-operativity are similar to the behaviour of t-PA itself. The results are discussed with regard to the molecular features involved in the mechanism of fibrin stimulation.
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PMID:Kinetic studies on novel plasminogen activators. Demonstration of fibrin enhancement for hybrid enzymes comprising the A-chain of plasmin (Lys-78) and B-chain of tissue-type plasminogen activator (Ile-276) or urokinase (Ile-159). 213 24

A rapid and quantitative fibrinolytic assay has been used to measure the overall activity of a recombinant tissue plasminogen activator (rTPA) preparation for dissolution of a fibrin clot by its ability to activate [Glu1]plasminogen (containing glutamic acid at position 1) to plasmin. A standard curve constructed for wild-type two-chain rTPA that contains, from the amino terminus, the finger (F)-growth factor (E)-kringle 1 (K1)-kringle 2 (K2)-serine protease (P) domains was used to assess the overall fibrin-dissolving abilities of variant recombinant molecules. Two-chain deletion mutants lacking the E domain, the F-E domains, the F-E-K1 domains, and the K1-K2 domains yielded activities ranging from 22% to 35% of the overall activity of wild-type two-chain rTPA, suggesting that both the K2 and F domains are individually responsible for a portion of the function of the molecule. Comparison of variant molecules containing F-K1-K2-P and F-K2-K2-P domains showed that the latter variant possessed a 4-fold higher activity (1.4-fold greater than that of wild-type two-chain rTPA), indicating that, for the activity measured, the presence of K2 leads to a greater effectiveness than that of K1. A plasmin cleavage-resistant mutant (Arg-275----Ser) has been used to assess possible differences in one- and two-chain rTPA in this overall activity, the former displaying 86% of the activity of the latter, suggesting that such differences are indeed small. Finally, the proper covalent attachment of the light and heavy chains of two-chain rTPA are very important to its overall fibrinolytic activity, since replacement of Cys-264 with glycine and concomitant disruption of one of the covalent attachment sites of the two chains provides a variant of rTPA with less than 2% of the activity of the wild-type two-chain molecule. The effector molecule, epsilon-amino hexanoic acid (epsilon Ahx; epsilon-aminocaproic acid), inhibits the overall fibrinolytic effect of rTPA in this system, with an effective Ki of approximately 1.5 mM. Its efficacy, as measured by the Ki, is independent of the presence of the epsilon Ahx binding regions of plasminogen and rTPA and is similar to the efficacy obtained when urokinase was the activator in place of wild-type two-chain rTPA or when activation of plasminogen was bypassed as a result of provision of preformed plasmin to the assay. The results suggest that in the overall clot lysis system, an important epsilon Ahx binding site may exist on fibrin that inhibits its dissolution by plasmin.
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PMID:Plasmin-mediated fibrinolysis by variant recombinant tissue plasminogen activators. 252 73

Endothelial cells play a critical role in thromboregulation by virtue of a surface-connected fibrinolytic system. Cultured endothelial cells synthesize and secrete tissue-type plasminogen activator (t-PA) which can bind to at least two discrete sites on the cell surface. These binding sites preserve the catalytic activity of t-PA and protect it from its physiological inhibitor (PAI-1). N-terminal glutamic acid plasminogen (Glu-PLG), the main circulating fibrinolytic zymogen, also interacts specifically with the endothelial cell surface. Binding is associated with a 12-fold increase in catalytic efficiency of plasmin generation by t-PA which may reflect conversion of Glu-PLG to its plasmin-modified form, N-terminal lysine plasminogen (Lys-PLG). Lipoprotein(a) is an atherogenic lipoprotein particle which contains the plasminogen-like apolipoprotein(a) bound to low density lipoprotein. We report here that lipoprotein(a) interferes with endothelial cell fibrinolysis by inhibiting plasminogen binding and hence plasmin generation. In addition, we demonstrate lipoprotein(a) accumulation in atherosclerotic lesions. These findings may provide a link between impaired cell surface fibrinolysis and progressive atherosclerosis.
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PMID:Lipoprotein(a) modulation of endothelial cell surface fibrinolysis and its potential role in atherosclerosis. 252 66

The effect of heparin on the proteolytic and fibrinolytic activities of plasmin and plasminogen was studied. Heparin at a concentration of 6.3.10(-6) M did not change the caseinolytic activity of plasmin and plasminogen stimulated by streptokinase but suppressed their fibrinolytic activity. At concentrations from 2.10(-8) to 0.5.10(-6) M heparin increased, whereas at 1.10(-6)-4.10(-6) M reduced the time of desAAfibrin clot half-lysis by plasmin. Within the concentration range of 2.10(-8) to 4.10(-6) M heparin did not change the time of the clot half-lysis by glu-plasminogen and slightly decreased the time of fibrin clot half-lysis by lys-plasminogen in the presence of the tissue activator. It was supposed that heparin inhibits the fibrinolytic effect of plasmin by way of formation of complexes with plasmin and reduction of plasmin specificity to the solid phase substrate, i. e., polymeric fibrin.
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PMID:[The effect of heparin on the proteolytic and fibrinolytic activity on plasmin(ogen) and fibrin clot lysis]. 253 55

A high-affinity surface receptor for human plasmin has been reported on certain group A streptococci. To map the region of the plasmin molecule that binds to the bacterial receptor, isolated domains of plasmin were tested for their ability to inhibit the binding of intact radiolabeled plasmin to receptor-positive bacteria. Complete inhibition of binding of labeled plasmin to bacteria by isolated heavy chains was achieved, but this inhibition was not as efficient on a molar basis when compared with that of unlabeled plasmin. By contrast, a conformationally altered form of native plasminogen was found to bind to bacteria and was as efficient a competitive inhibitor as intact plasmin was. The results of this study indicate that the selective binding of human plasmin to a group A streptococcus is dependent on structures present in the conformationally altered form of native plasminogen or plasmin that are not found on the native zymogen, the plasminogen with NH2-terminal glutamic acid.
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PMID:Mapping of the human plasmin domain recognized by the unique plasmin receptor of group A streptococci. 254 17


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