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)

To further investigate which parts of the fibrinogen molecule that are responsible for its binding to the fibrinogen receptor on human platelets, the following approaches were made: The glycoprotein IIb-IIIa complex (the putative fibrinogen receptor) was immunoprecipitated in crossed immunoelectrophoresis of Triton X-100-extracts of platelets against antibodies to whole platelet proteins. Subsequently, the immunoplates were incubated with 125I-labelled, plasmin- or CNBr-cleaved fibrinogen fragments (pre-X,X,Y,D,Degta,Efg,N-DSK) or fibrin fragments (E1,N-dsk), characterized by partial sequenation. The immunoplates were exposed to X-ray films, and binding of the fragments to the glycoprotein IIb-IIIa complex was examined. The findings were compared to the results obtained from studies on binding of the same fragments to intact gel-filtered platelets after ADP-stimulation. The following conclusions were made: All fragments except Efg and Degta bound to the immunoprecipitated GPIIb-IIIa complex as well as to ADP-stimulated platelets suggesting that at least two sequences in the E domain and one in each of the D domains of fibrinogen are involved in binding to the platelet receptor. The GPIIb-IIIa complex is the only surface-located platelet antigen that binds fibrinogen and the aforementioned fragments. The binding of the fragments to the receptor is dependent on divalent cations.
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PMID:Binding of 125I-labelled fibrin(ogen) fragments to platelets and to immunoprecipitated glycoprotein IIb-IIIa complex. 242 22

Tissue plasminogen activator (TPA) converts plasminogen to plasmin within the fibrin clot, thus localizing activation of fibrinolysis. To determine the extent to which platelets promote activation of plasminogen by TPA, we studied the interaction of TPA and plasminogen with unstimulated platelets. Normal washed platelets incubated in the presence of physiologic concentrations of plasminogen (180 micrograms/mL) and TPA (20 ng/mL) failed to generate plasmin activity. In contrast, incubation of platelets with TPA concentrations achieved during thrombolytic therapy (40 to 800 ng/mL) produced a tenfold to 50-fold increase in plasmin activity. After exposure to plasminogen and 200 ng/mL of TPA for one hour, platelets failed to agglutinate in the presence of ristocetin. Incubation of platelets suspended in autologous plasma with 400 ng/mL of TPA for one hour also inhibited ristocetin-induced agglutination. Exposure of platelets to plasminogen and increasing concentrations of TPA correlated with a decrease in glycoprotein Ib (GPIb) and an increase in glycocalicin, as shown by immunoblotting. The glycoprotein IIb/IIIa (GPIIb/IIIa) complex and a 250,000-dalton protein also disappeared from washed platelets after incubation with plasminogen and 200 ng/mL of TPA for one hour. These platelets failed to aggregate in the presence of adenosine diphosphate (ADP) or gamma thrombin, although aggregation in response to calcium ionophore A23187 and arachidonic acid remained intact. However, aggregation in response to all four agonists was normal when platelets were incubated with TPA in the presence of autologous plasma. Platelets from a patient with Glanzmann's thrombasthenia also generated plasmin in the presence of TPA. Hydrolysis of GPIb and inhibition of ristocetin-induced agglutination occurred to a lesser extent with these platelets than with control platelets. We conclude that platelets provide a surface for activation of plasminogen by pharmacologic amounts of TPA. Plasmin generation leads to degradation of GPIb and decreased ristocetin-induced agglutination in normal and thrombasthenic platelets, as well as degradation of GPIIb/IIIa in normal washed platelets and inhibition of ADP and gamma thrombin-induced aggregation. These findings suggest that pharmacologic concentrations of TPA may cause platelet dysfunction due to plasmin generation on the platelet surface.
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PMID:Activation of plasminogen by tissue plasminogen activator on normal and thrombasthenic platelets: effects on surface proteins and platelet aggregation. 294 Oct 84

We have previously established that the mitogenic effect of fibrinogen on hemopoietic cell lines Raji and JM is mediated via a specific receptor (Levesque, J.-P. et al.: Proc. Natl. Acad. Sci. USA 83:6494-6498, 1986). In this study, we have further characterized the fibrinogen domain involved in the binding to the mitogenic receptor. This binding was not inhibited either by a monoclonal antibody against the C-terminal sequence of the fibrinogen gamma chains or by synthetic peptides containing the Arg-Gly-Asp sequence. Such inhibition is specific of the platelet fibrinogen receptor, the glycoprotein IIb-IIIa complex. Fragments containing the fibrinogen D domain were the only plasmin degradation products of fibrinogen which were mitogenic. These fragments acted via direct binding on the mitogenic receptor with a Kd of 2.24 X 10(-6) M. This value was similar to the KI value of unlabeled fragments D (2.47 X 10(-6) M). Our results suggest the presence of two different functional types of fibrinogen receptors: the glycoprotein IIb-IIIa receptor responsible both for platelet aggregation and leukocyte adhesion and killing, and the mitogenic receptor involved in proliferation control of hemopoietic cells.
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PMID:Evidence for two functionally different fibrinogen receptors on hemopoietic cells: the glycoprotein IIb-IIIa and the mitogenic fibrinogen receptor. 362 17

Plasmin exposure modulates platelet aggregation responses, but a direct effect of plasmin on the platelet fibrinogen receptor, glycoprotein IIb/IIIa (GPIIb/IIIa), has never been conclusively shown in a plasma milieu. To examine this issue, we incubated platelets in platelet-rich plasma with plasmin and measured the effect of this treatment on platelet aggregation, fibrinogen binding, and the structural integrity of GPIIb/IIIa. Plasmin treatment reduced maximal reversible fibrinogen binding in a dose-dependent fashion, and this reduction in binding was accompanied by a correlative reduction in the maximal rate of aggregation. Immunoblots performed with polyclonal antibodies against GPIIb/IIIa showed that GPIIIa had been cleaved by plasmin, but this cleavage was detected only after subsequent degradation of the solubilized GPIIb/IIIa with Staphylococcus aureus V8 (Glu-C) endoprotease. Peptide sequence analysis showed that cleavage occurred at the lys444-pro445 bond in the first cysteine-rich repeat domain of GPIIIa a unique proteolytic event observed only in the presence of plasma fibrinogen. These observations suggest that plasmin modifies GPIIIa by a unique proteolytic event in plasma that is dependent on fibrinogen binding and, consequently, is accompanied by significant reductions in fibrinogen binding and aggregation response.
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PMID:Structural changes in platelet glycoprotein IIb/IIIa by plasmin: determinants and functional consequences. 828 40

The synthesis and design using molecular modeling techniques for non-peptide, low molecular weight novel fibrinogen receptor (glycoprotein IIb/IIIa: Gp IIb/IIIa) antagonists, is reported. We used a highly potent serine protease inhibitor, Nafamostat, having an amidinonaphthyl unit as the starting compound. The compounds 4-(6-amidino-2-naphthylaminocarbonyl)phenoxyacetic acid (5a) and 4-(6-amidino-2-naphthalenecarboxamido)phenoxyacetic acid (5b) inhibited adenosin-5'-diphospate (ADP)-induced aggregation of human platelet-rich plasma (PRP) with IC50 values of 0.05 and 0.07 microM, respectively, and had lost their ability to inhibit a variety of serine proteases, including thrombin, factor Xa, plasmin and trypsin.
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PMID:Preparation and pharmacological evaluation of novel glycoprotein (Gp) IIb/IIIa antagonists. 1. The selection of naphthalene derivatives. 1074 13

Plasminogen activator inhibitor-1 (PAI-1) and alpha2-anti-plasmin (alpha2-AP) may contribute to arterial thrombolysis resistance. The role of these components on thrombus evolution in vivo was investigated in mice deficient for PAI-1 (PAI-1(-/-)) or alpha2-AP (alpha2-AP(-/-)) or their wild-type counterparts (PAI-1(+/+), alpha2-AP(+/+)). Moreover, the influence of either PAI-1 or alpha2-AP deficiency on the results of pharmacologic inhibition of glycoprotein IIb/IIIa of platelets or thrombin was also investigated. A thrombus was induced in the murine carotid artery by endothelial injury. The alpha2-AP(-/-) mice were indistinguishable from wild-type, whereas the time to occlusion in PAI-1(-/-) was significantly prolonged to 24.9 +/- 3.7 min. Vascular patency was markedly increased in both PAI-1- and alpha2-AP-deficient mice. In separate animals, either a glycoprotein IIb/IIIa antagonist or a thrombin inhibitor was applied. The time required to occlusion was prolonged in a dose-dependent manner in all types of mice. When each compound was administered to PAI-1(-/-) mice, significant changes were observed. In conclusion, lack of PAI-1 prolongs the time to occlusion and accelerates clot lysis, whereas alpha2-AP only has an effect on spontaneous reperfusion. Consequently, the inhibition of PAI-1, but not of alpha2-AP, could enhance the effects of anti-thrombotic therapy.
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PMID:Inhibitors of fibrinolytic components play different roles in the formation and removal of arterial thrombus in mice. 1179 Oct 14

Plasmin-dependent thrombolytic agents are potentially prothrombotic and proinflammatory. Alfimeprase, a zinc-containing metalloproteinase, degrades fibrin directly and achieves thrombolysis independent of plasmin formation. This study examines the hypothesis that thrombolysis in the absence of plasmin generation results in improved myocardial salvage on reperfusion. The thrombolytic effects of recombinant tissue plasminogen activator [rt-PA; 0.022 mg/kg, 1/10 of which was administered as a loading dose; the rest (9/10) was infused over 60 min by intracoronary (ic) administration] or alfimeprase (0.5 mg/kg over 1 min ic) were evaluated in a canine model of arterial thrombosis involving electrolytic injury of the left circumflex (LCX) coronary artery. Both agents induced thrombolysis, with onset of reperfusion being more rapid after alfimeprase compared with rt-PA (1.5 +/- 0.6 vs. 10.1 +/- 2.1 min). In the absence of adjunctive therapy, time to reocclusion after alfimeprase was 3.2 +/- 0.5 min compared with 77.5 +/- 31.9 min with rt-PA. The glycoprotein IIb/IIIa platelet receptor antagonist CRL-42796 prolonged reperfusion time after thrombolysis with alfimeprase or rt-PA. The effect of each lytic agent on myocardial infarct size was examined in a separate group of dogs subjected to 60 min of LCX coronary artery ligation and 4 h of reperfusion. Myocardial infarct size, expressed as percentage of the risk region, was larger (32.16 +/- 3.95%) after rt-PA compared with alfimeprase (19.85 +/- 3.61%) or that of the saline control group (18.46 +/- 3.34%). rt-PA in contrast to alfimeprase, a direct-acting fibrinolytic agent, is associated with an increase in myocyte reperfusion injury.
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PMID:Effect of thrombolysis on myocardial injury: recombinant tissue plasminogen activator vs. alfimeprase. 1624 15

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