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:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study of the platelet membrane fibrinogen binding site, called glycoprotein IIb/IIIa, the final common pathway for platelet aggregation, measured receptor density (Bmax) and affinity (Kd) in men and women of all ages and in cycling women and in those using oral contraceptives. The subjects were 37 women aged 21-91, 23 men aged 20-83, women aged 21-33 using low-dose combined oral contraceptives containing 30-35 mcg estrogen and 150-500 mcg progestin, compared to 8 menstruating women aged 21-43. The assay measured Iodine-125-fibrinogen binding to gel-filtered platelets stimulated with ADP and thrombin. There were no significant differences between the sexes for Bmax or Kd. A trend towards increasing affinity (reduced Kd) with age was seen in women after ADP stimulation, which was within normal limits and judged not of clinical significance. There were also no significant differences in the comparison of cycling and pill using women on cycle days 7, 14, 21 and 28, between groups or phases. Thus glycoprotein II/IIIa, the final common mediator of platelet aggregation, is a stable entity with little variation with age, gender or altered hormonal status.
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PMID:Effects of age, sex and the oral contraceptive on the platelet membrane fibrinogen binding site (glycoprotein IIb/IIIa). 154 Apr 80

We recently reported that after activation of human platelets by thrombin, glycoprotein (GP) Ib-IX complexes are translocated to the surface-connected canalicular system (SCCS) (Blood 76:1503, 1990). As GPIb is a major receptor for von Willebrand factor (vWF) in platelet adhesion, we have now examined the consequences of thrombin activation on the organization of vWF bound to GPIb on the platelet surface. Studies were performed using monoclonal or polyclonal antibodies in either immunogold staining and electron microscopy (Au-EM) or in flow cytometry. When unstirred platelet-rich plasma was incubated with ristocetin, bound vWF was located by Au-EM as discrete masses regularly distributed over the cell surface. Platelets from a patient with Glanzmann's thrombasthenia, lacking GPIIb-IIIa complexes, gave a similar pattern, confirming that this represented binding to GPIb. That ristocetin was not precipitating vWF before their binding to the platelets was shown by the detection of similar masses on the surface of platelets of a patient with type IIB von Willebrand disease. Experiments were continued using washed normal platelets incubated in Tyrode-EDTA, the purpose of the EDTA being to limit the surface expression of endogenous vWF after platelet stimulation. Under these conditions, platelets were treated with ristocetin for 5 minutes at 37 degrees C in the presence of increasing amounts of purified vWF. This was followed by incubation with thrombin (0.5 U/mL) for periods of up to 10 minutes. Flow cytometry showed a time-dependent loss in the surface expression of vWF bound to GPIb and these changes were confirmed by Au-EM. In particular, immunogold staining performed on ultrathin sections showed that the bulk of the vWF was being cleared to internal membrane systems. Surface clearance of vWF during thrombin-induced platelet activation is a potential mechanism for regulating platelet adhesivity.
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PMID:von Willebrand factor bound to glycoprotein Ib is cleared from the platelet surface after platelet activation by thrombin. 156 27

We describe a new variant of Glanzmann's thrombasthenia (variant Strasbourg I). The patient (M.S.) showed an absence of platelet aggregation to ADP, thrombin, and collagen, and a decreased clot retraction. Platelet fibrinogen was approximately 20% of normal levels. ADP-stimulated platelets bound markedly reduced amounts of soluble fibrinogen and platelet adhesion to surface-bound fibrinogen was defective. Normal to subnormal amounts of glycoprotein (GP) IIb-IIIa (alpha IIb beta 3) complexes, the platelet fibrinogen receptor, were revealed by SDS-PAGE, crossed immunoelectrophoresis, and antibody binding. However, the complexes were unusually sensitive to dissociation with EDTA at room temperature. Furthermore, flow cytometry showed that the platelets failed to bind the activation-dependent monoclonal antibody, PAC-1, after stimulation. In contrast, an RGDS-containing peptide induced significant binding of the anti-ligand-induced binding site antibody, D3GP3, suggesting the presence of a functional RGD binding domain on the patient's GPIIb-IIIa complex. Sequence analysis was performed after polymerase chain reaction amplification of selected patient's GPIIIa exons, and of the patient's platelet GPIIb and GPIIIa mRNAs. A point mutation (C to T) was localized in exon D (iv) of GPIIIa that resulted in an 214Arg to 214Trp amino acid substitution. The defect has been inherited from the parents who are heterozygous for the same mutation. This substitution points to an essential amino acid in a region of GPIIIa involved in the binding of fibrinogen and influencing the Ca(2+)-dependent stability of the GPIIb-IIIa complex.
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PMID:A new variant of Glanzmann's thrombasthenia (Strasbourg I). Platelets with functionally defective glycoprotein IIb-IIIa complexes and a glycoprotein IIIa 214Arg----214Trp mutation. 160 6

The presence of platelet fragments or platelet-derived microparticles (MP) in blood is of great interest, because it could be used as a marker for increased destruction or activation of platelets followed by their aggregation and vesiculation. In addition to early electronmicroscopic observations, a variety of methods to detect MP in plasma and serum have been developed, including immunoelectrophoresis, radioimmunoassay and the immunofluorescence test using flow cytometric analysis. In these techniques, monoclonal antibodies directed against platelet membrane specific antigens, such as glycoprotein (GP) IIb/IIIa or GP I b, have been used to distinguish platelet microparticles from other components. From basic and clinical investigations, MP has proved to be increased in some physiological and pathological conditions, including blood clotting, thrombin and collagen-induced activation of platelets, mechanical trauma of platelets, and immune-mediated platelet destruction. Furthermore, it has been shown that a significant part of platelet procoagulant activity resides on these small vesicles (MP), released from the platelet plasma membrane, on activation.
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PMID:[Platelet-derived microparticles]. 161 88

Protease nexin I (PNI), a 43,000- to 50,000-dalton glycoprotein, is a potent thrombin and urokinase inhibitor produced by many mammalian cells, including human glia, in tissue culture. PNI is a member of the growing superfamily of serine protease inhibitors now known as serpins, but, unlike many others of this family, it has not yet been detected in normal human plasma. Of interest to neurobiology and neurologic disease, PNI is identical to a glia-derived neurite-promoting factor, glia-derived nexin (GDN). Antibody to PNI stains the periphery of senile amyloid plaques in brain tissue from patients with Alzheimer's disease (AD), along with another serpin, alpha 1-antichymotrypsin (alpha 1-ACT). A soluble form of the beta-amyloid precursor protein (beta APP), containing a Kunitz-type trypsin inhibitor domain, the beta APP751 form, is identical to protease nexin II (PNII), a 100,000-dalton serine protease inhibitor present in a number of tissues besides the brain. PNII/beta APP is also found in normal and AD CSF. We found a 47,000-dalton PNI, a thrombin- and urokinase-inhibiting serpin, in normal human CSF by Western blotting using a monospecific antibody. We also demonstrated biologically active PNI capable of forming complexes with serine proteases 125I-urokinase or 125I-thrombin.
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PMID:Protease nexin I, thrombin- and urokinase-inhibiting serpin, concentrated in normal human cerebrospinal fluid. 162 Mar 46

During activation of platelets by agonists, a number of proteins become phosphorylated at tyrosine residues. Using immunoblotting with a monoclonal anti-phosphotyrosine antibody, we have compared the different phosphotyrosine-protein (PTP) profiles of platelets stimulated with thrombin, collagen, ADP, arachidonic acid, phorbol myristate acetate and P256, an anti-glycoprotein-IIb-IIIa (GPIIb-IIIa) monoclonal antibody (mAb). Only a few PTPs were observed in resting platelets, of molecular masses 130, 64, 56-60 and 36 kDa. After stimulation by different agonists these proteins were more intensely phosphorylated and additional PTPs appeared with molecular masses of 170, 150, 140, 120, 105/97 (doublet), 85, 80, 75 and 45 kDa. The kinetics of phosphorylation differed from one agonist to another, but no significant differences in the overall patterns were detected, except in presence of ADP and P256-F(ab')2, which induced only the additional tyrosine phosphorylation of the 64 kDa protein and to a lesser extent that of a 75 kDa protein. The use of various agonists and the inhibitors (staurosporine, ajoene and RGDS) permitted a better characterization of the relationship between the different steps of activation and phosphorylation on tyrosine residues. The studies suggest the following conclusions: (i) stimulation of tyrosine phosphorylation occurs after activation of protein kinase C; (ii) there is a relationship between ligand binding to GPIIb-IIIa and the tyrosine phosphorylation of the 64 kDa protein; and (iii) there is a close relationship between PTP formation and the intensity of platelet activation and aggregation.
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PMID:Functional implications of tyrosine protein phosphorylation in platelets. Simultaneous studies with different agonists and inhibitors. 162 7

Antithrombin is the most important physiological proteinase inhibitor of thrombin and other coagulation proteinases. It is a single chain glycoprotein of MW 58,200 which has sequence homology with alpha 1-antitrypsin and other members of the serpin superfamily of inhibitors. Two functional domains of importance have been identified, the reactive centre that interacts with the proteinase and a heparin binding domain. Failure to maintain an adequate level of functional antithrombin in plasma results in an increased risk of thromboembolism: deficiency can be inherited or acquired. There is still uncertainty regarding the prevalence of inherited deficiency and the prevalence of thrombosis in affected individuals. The production of antithrombin is under the control of a single gene which is localized on chromosome 1q 23-25. Characterization of the coding sequence, which is distributed over seven exons, has allowed the analysis of the molecular basis for inherited antithrombin deficiency. To date more than 100 cases have been successfully investigated at the gene and/or protein sequence level and 40 novel mutations have been identified. Mutations causing amino acid substitutions solely affecting the heparin binding site have thus far been located primarily at the N-terminal region of the molecule, residues 7-129; this region has been postulated to align as a positive groove in the molecule that forms the primary contact region for the essential antithrombin binding pentasaccharide of heparin. Not all the residues in which substitutions have been found are basic and some serve to maintain the conformation of nearby basic regions. Examples of this are provided by the Pro-41 to Leu mutation and a recently investigated mutant, Leu-99 to Phe. The reactive site defects are an interesting group, including those that alter P1, P1' and P12-P10 residues. Perhaps more remote mutations can also be included such as Pro-429 to Leu. The P1 and P1' mutations directly block interaction of the proteinase with anti-thrombin, while P12-P10 mutants (which have mutations affecting serpin strand s4A) enable the substrate reaction to proceed to completion, i.e. the antithrombin-thrombin complex is not stabilized and the mutant inhibitor is transformed into a substrate. The effect of the Pro-429 to Leu substitution is impairment of the reactive site and heparin binding, and the finding that this variant is not completely recognized by some MAbs implies a conformational change at the C terminus. Another group (nine cases) of interesting mutations is emerging, that has its primary defect in or near serpin strand 1C, amino acid sequence 402-407.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Antithrombin and its deficiency states. 164 10

The involvement of platelet glycoprotein (GP) IIb-IIIa complex in calcium channel activity on the plasma membrane was investigated using an electrophysiological approach. Plasma membrane vesicles were prepared from thrombin-stimulated platelets and incorporated into planar lipid bilayers. Voltage-independent Ca2+ channel currents with a conductance of about 10 pS (in 53 mM Ba2+) were observed, in membranes derived from thrombin-stimulated, but not unstimulated platelet membranes. These channel activities were markedly reduced by exposure of membranes to EGTA at 37 degrees C. This reduction was specifically related to the dissociation of the GPIIb-IIIa complex since preincubation of the membranes with a monoclonal antibody to the GPIIb-IIIa complex (AP-2) could protect the channel activities from the effect of EGTA. Thrombasthenic platelets, which lack the GPIIb-IIIa complex, showed impaired channel activities characterized by decreased open probability and lowered conductance states. Furthermore, when platelets were stimulated by thrombin in the presence of EGTA, AP2, or the synthetic peptide RGDS, to prevent fibrinogen binding to the GPIIb-IIIa complex, open probabilities of the channel currents in these membrane vesicles were also decreased. These results suggest that the GPIIb-IIIa complex is involved in platelet Ca2+ channel activation and that ligand binding to the complex during platelet activation may modify the activation of Ca2+ channels.
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PMID:Electrophysiological evidence that glycoprotein IIb-IIIa complex is involved in calcium channel activation on human platelet plasma membrane. 165 31

32P-Labeled human platelets were incubated with thrombin (1 unit/ml) for 5 min at 37 degrees C under conditions allowing maximal synthesis of [32P]phosphatidylinositol 3',4'-bisphosphate (PtdIns(3,4)P2). Incorporation of 32P into the latter phosphoinositide was dose-dependently reduced (to a maximal level averaging 60%) by the tetrapeptide RGDS, an inhibitor of fibrinogen binding to activated glycoprotein IIb-IIIa (alpha IIb-beta 3 integrin). Identical results were obtained with the fibrinogen gamma-chain dodecapeptide HHLGGAKQAGDV, whereas the tripeptide RGD and the tetrapeptide RGES displayed reduced or undetectable effects on 32P labeling of PtdIns(3,4)P2, respectively, in good correlation with their ability to inhibit platelet aggregation and fibrinogen binding to activated alpha IIb-beta 3 integrin. In addition, pathological platelets from three patients suffering thrombasthenia, which lack alpha IIb-beta 3 integrin and fail to aggregate in response to thrombin, displayed hardly detectable increases in the 32P labeling of PtdIns(3,4)P2. In contrast, thrombin-stimulated synthesis of PtdIns(3,4)P2 was unaltered in other deficient platelets lacking the glycoprotein Ib-IX complex (Bernard-Soulier syndrome). Although additional pathways seem to be involved in the regulation of phosphatidylinositol-3-kinase, these data indicate a strong relationship between platelet aggregation involving fibrinogen binding to activated alpha IIb-beta 3 integrin and the synthesis of the novel phosphoinositides phosphorylated at position D-3 of the inositol ring.
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PMID:Involvement of platelet glycoprotein IIb-IIIa (alpha IIb-beta 3 integrin) in thrombin-induced synthesis of phosphatidylinositol 3',4'-bisphosphate. 166 Aug 76

Elevated levels of plasma homocysteine are associated with both venous and arterial thrombosis. Homocysteine inhibits the function of thrombomodulin, an anticoagulant glycoprotein on the endothelial surface that serves as a cofactor for the activation of protein C by thrombin. The effects of homocysteine on thrombomodulin expression and protein C activation were investigated in cultured human umbilical vein endothelial cells and CV-1(18A) cells that express recombinant human thrombomodulin. Addition of 5 mM homocysteine to endothelial cells produced slight increases in thrombomodulin mRNA and thrombomodulin synthesis without affecting cell viability. In both cell types, thrombomodulin synthesized in the presence of homocysteine remained sensitive to digestion with endoglycosidase H and failed to appear on the cell surface, suggesting impaired transit along the secretory pathway. In a cell-free protein C activation assay, homocysteine irreversibly inactivated both thrombomodulin and protein C in a process that required free thiol groups and was inhibited by the oxidizing agents diamide or N-ethylmaleimide. By inhibiting both thrombomodulin surface expression and protein C activation, homocysteine may contribute to the development of thrombosis in patients with cystathionine beta-synthase deficiency.
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PMID:Inhibition of thrombomodulin surface expression and protein C activation by the thrombogenic agent homocysteine. 166 Dec 91


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