Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.73 (urokinase-type plasminogen activator)
 10,685 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Highly purified pro-urokinase (pro-UK) or single-chain urokinase-type plasminogen activator (scu-PA) was treated with diisopropylfluorophosphate (1 mmol/L) to eliminate traces of two-chain UK activity. This preparation was found to retain a low activity against a chromogenic substrate (S2444), equivalent to 0.1% to 0.5% of the activity of its plasmin-activated derivative. Evidence is presented that the intrinsic activity of pro-UK (scu-PA) was sufficient to activate plasminogen on a fibrin plate or in buffer and was far more reactive against Lys-plasminogen than against Glu-plasminogen. The relative resistance of Glu-plasminogen to activation was overcome by the addition of lysine (25 mmol/L) to the reaction mixture. By contrast, in plasma, pro-UK (scu-PA) was stable and nonreactive for greater than 72 hours when incubated (37 degrees C). Pro-UK (scu-PA) did not form sodium dodecyl sulfate-stable inhibitor complexes, whereas complexation occurred rapidly with UK. Only at high concentrations of pro-UK (scu-PA) (greater than or equal to 250 IU/mL) did plasminogen activation in plasma occur. The relative inertness of pro-UK (scu-PA) in plasma, in contrast to its low-grade enzymatic activity in buffer, was attributed to the effect of inhibitors. The addition of EDTA or the removal of divalent cations by dialysis was associated with a lower threshold for nonspecific plasminogen activation by pro-UK (scu-PA) in plasma. Replacement of Ca++ but not other cations restored baseline conditions. In the presence of a clot, fibrin-selective plasminogen activation and clot lysis were triggered. Lysis was accompanied by less than 10% conversion of pro-UK (scu-PA) to two-chain UK, suggesting that the intrinsic activity of pro-UK (scu-PA) itself may have been responsible for fibrinolysis, although a contribution by the small amount of UK generated could not be excluded. Similarly, pro-UK (scu-PA) supported clot lysis for several days in the same plasma before the effect dissipated as a result of degradation to UK. When Glu-plasminogen in plasma was replaced by Lys-plasminogen, or when lysine was added to normal plasma, nonselective plasminogen activation and fibrinogenolysis occurred. It was concluded that under the experimental conditions, the fibrin specificity of pro-UK (scu-PA) can be explained by its selective activation of fibrin-bound plasminogen and is due to the latter's Lys-plasminogen-like conformation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Pro-urokinase: a study of its stability in plasma and of a mechanism for its selective fibrinolytic effect. 308 89

Plasminogen activation at the surface of fibrin or of cell membranes is a sophisticated specialized system for localized extracellular proteolysis implicated in a large variety of biological functions (fibrinolysis, cell migration and extracellular matrix degradation). Assembly of plasminogen and/or activators at specific binding sites induces conformational changes that make accessible the scissile peptide bond of plasminogen and exposes the active centre of the tissue-type plasminogen activator. The mechanism of activation by pro-urokinase, a second type of activator that binds to cell membrane but not to fibrin, is far from being understood. It may be able, however, in contrast to urokinase, to specifically activate plasminogen bound to partially degraded fibrin. An extremely low Km and high catalytic rate are characteristic of the process of activation at surfaces. In contrast, activation in liquid phase by tissue-type plasminogen activator proceeds at an extremely low catalytic rate. The initiation and amplification of plasminogen activation depend on specific interactions between the modular constitutive units of these proteins and binding sites present on cell or fibrin surfaces. Thus, the most important mechanism for the acceleration of fibrinolysis and pericellular proteolysis is the unveiling of carboxy-terminal lysine residues on these surfaces, to which plasminogen may bind. Since plasminogen bound to carboxy-terminal lysines of progressively degraded fibrin or membranes is readily transformed into plasmin by fibrin-bound t-PA, this mechanism represents the most important pathway for the acceleration and amplification of fibrinolysis. Alpha-2-antiplasmin, by inhibiting plasmin release from surfaces, regulates the extent and rate of this process but has no effect on fibrin-bound or membrane-bound plasmin. Lipoprotein(a), a particle possessing a plasminogen-like apolipoprotein, apo(a), may interfere with this mechanism by inhibiting the specific binding of plasminogen to lysine residues in membrane or fibrin surfaces.
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PMID:Overview on fibrinolysis: plasminogen activation pathways on fibrin and cell surfaces. 818 35

Monoclonal antibodies directed against recombinant apolipoprotein (a) (r-apo(a)) lacking plasminogen-like KIV-2 repeats were used to identify structurally related conformational epitopes in various members of the plasminogen-prothrombin gene family. A number of procedures including a fibrin-binding inhibition immunoassay and surface plasmon resonance studies were used. Two antibodies (A10.1 and A10.4) recognised common conformational structures in r-apo(a), prothrombin, factor XII, plasminogen and its tissue-type and urokinase-type activators. In contrast, two other antibodies recognised specifically an epitope comprising residues of the lysine-binding site (A10.2) or close to it (A10.5) and inhibited the fibrin-binding function of r-apo(a) (IC(50)=36 pmol/l and 9.76 nmol/l, respectively). Interestingly, these antibodies distinctly recognised the elastase-derived fragments of plasminogen K4 (A10.2) and K1+2+3 (A10.5) without affecting plasminogen binding to fibrin. These results suggest that highly conserved conformational regions are common to various proteins of the plasminogen-prothrombin gene family and are in agreement with the concept that these proteins constitute a monophyletic group derived from an ancestral gene.
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PMID:Kringles of the plasminogen--prothrombin gene family share conformational epitopes with recombinant apolipoprotein (a): specificity of the fibrin-binding site. 1145 40

In the search for new ligands for the plasminogen kringle 4 binding-protein tetranectin, it has been found by ligand blot analysis and ELISA that tetranectin specifically bound to the plasminogen-like hepatocyte growth factor and tissue-type plasminogen activator. The dissociation constants of these complexes were found to be within the same order of magnitude as the one for the plasminogen-tetranectin complex. The study also revealed that tetranectin did not interact with the kindred proteins: macrophage-stimulating protein, urokinase-type plasminogen activator and prothrombin. In order to examine the function of tetranectin, a kinetic analysis of the tPA-catalysed plasminogen activation was performed. The kinetic parameters of the tetranectin-stimulated enhancement of tPA were comparable to fibrinogen fragments, which are so far the best inducer of tPA-catalysed plasminogen activation. The enhanced activation was suggested to be caused by tetranectin's ability to bind and accumulate tPA in an active conformation.
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PMID:Tetranectin binds hepatocyte growth factor and tissue-type plasminogen activator. 1269 98

Apolipoprotein(a), the plasminogen-like component of lipoprotein(a), is transformed into fragments by polymorphonuclear neutrophils (PMNs) elastase. Since stimulated PMNs express urokinase-type plasminogen activator (uPA), we sought to investigate the relevance of apo(a) fragmentation on plasminogen activation by neutrophils. Freshly isolated human PMNs stimulated by a 10 kringle recombinant apo(a), r-apo(a), activate plasminogen in a specific and saturable manner (Km = 476 +/- 42 nM, Vmax = 896 +/- 18 pmol min(-1)). This activation is prevented by amiloride, an inhibitor of u-PA, and epsilon-aminocaproic acid, epsilon-ACA, a lysine analogue that blocks plasminogen binding to PMNs. Stimulation of PMNs by apo(a) results in the formation of elastase-derived apo(a) fragments. These fragments produce a concentration-dependent decrease in the formation of plasmin. Addition of elastase inhibitors to PMNs prevented degradation of apo(a) and partially restored the formation of plasmin. In a similar manner, isolated r-apo(a) fragments were able to produce a 100% decrease in plasmin generation as compared to intact r-apo(a). These data indicate that apo(a) fragments produce a more pronounced inhibition in the generation of cell-bound plasmin by uPA than the parent apo(a). These effects of apo(a) and its fragments were neutralised by a monoclonal antibody directed against the lysine-binding site of apo(a). This mechanism may be of biological relevance to the effects of Lp(a) in conditions where PMNs accumulate and release elastase, i.e. thrombus lysis and inflammatory lesions.
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PMID:Neutrophils stimulated by apolipoprotein(a) generate fragments that are stronger inhibitors of plasmin formation than apo(a). 1554 35

Plg (plasminogen), a member of the serine protease superfamily, is a key component constituting the fibrinolytic system, and its evolutionary origin remains unknown during the course of animal evolution. In the present study, we isolated a cDNA, designated BbPlgl, encoding a kringle-containing protease with plasminogen-like activity from the basal chordate Branchiostoma belcheri. The deduced protein, BbPlgl, consisted of 430 amino acids, which is structurally characterized by the presence of an N-terminal signal peptide of 16 amino acids, 2 kringle domains with a Lys-binding site structure, a serine protease domain with the putative tPA (tissue plasminogen activator)-cleavage site (between Arg297 and Val298), the catalytic triad His237-Asp288-Ser379 expected for protease function, and a potential N-linked glycosylation site, all characteristic of Plgs. Besides, the recombinant refolded BbPlgl was readily activated by human uPA (urokinase plasminogen activator), and exhibited Plg-like activity. BbPlgl was also able to auto-activate at neutral and alkaline pH at 4 degrees C without the addition of uPA, and the activation was accelerated by addition of human uPA. These results demonstrate that BbPlgl is a novel member of the Plg family, with a domain structure of K-K-SP (kringle-kringle-serine protease) lacking the PAN domain, pushing the evolutionary origin of Plg to the protochordate. In addition, BbPlgl displays a tissue-specific expression pattern in B. belcheri, with the most abundant expression in the hepatic caecum and hind-gut, agreeing with the notion that the hepatic caecum of amphioxus is the precursor of the vertebrate liver.
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PMID:A kringle-containing protease with plasminogen-like activity in the basal chordate Branchiostoma belcheri. 1919 94