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

---

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

High concentrations of bovine factor VIII cause clumping of platelets into a few very large aggregates. This response is termed superaggregation. It is distinct from factor-VIII-induced agglutination but is also independent of both extracellular calcium ions and platelet energy metabolism. Neither agglutinating lectins nor aggregating agents, including thrombin, ADP, the ionophore A23187, and U46619, a prostaglandin analog, can induce superaggregation, even at very high concentrations. Washed platelets undergo superaggregation, and superaggregation does not increase the amounts of fibrinogen or albumin trapped by agglutinated platelets. It is not inhibited by membrane-stabilizing drugs or by colchicine or cytochalasin-B. Formaldehyde and glutaraldehyde prevent superaggregation without affecting the binding of radiolabeled factor VIII to the platelets. Superaggregated platelets are separated by approximately 50 nm and are not shape-changed or degranulated. In adenosine diphosphate (ADP) induced aggregation, the platelets are distorted and only 30 nm apart. Superaggregation is reversed by dextran sulfate, and the dispersed platelets are still able to respond to ADP. Our observations are consistent with the binding of high molecular weight multimers of bovine factor VIII to more than one receptor on each platelet, with superaggregation occurring through recruitment of additional receptors. This process may be interrupted by protein crosslinking reagents, such as formaldehyde and glutaraldehyde.
...
PMID:Factor VIII-induced superaggregation of human platelets. 681 50

The role of fibrinogen in interplatelet recognition during aggregation was examined by combining two cell types: fresh platelets (in limiting density) activated by thrombin or A23187, and formaldehyde-fixed platelets, bearing cross-linked fibrinogen. The fixed platelets did not aggregate by themselves, nor with resting platelets, but were capable of interacting with activated platelets and of participating passively in aggregation. The participation, expressed by enhanced aggregation, was assayed by the conventional turbidometric traces and by cosedimentation of fixed 3H-platelets with aggregates of fresh platelets. Platelet suspensions, prepared without special means to avert spontaneous activation, retained plasma fibrinogen to the extent of 50 micrograms/ml of a suspension containing 10(8) platelets, and the derived fixed platelets participated in aggregation, independently of added fibrinogen. The capability of such fixed platelets to participate in aggregation was sensitive to proteolytic digestion and to massive acetylation. When platelet separation was aided by apyrase or aspirin, PGE1 and gel filtration, the residual plasma fibrinogen was limited to 0.4 micrograms/ml of 10(8) platelet suspension. The derived fixed platelets were incapable of participating in aggregation unless fibrinogen was added prior to fixation. The affixed fibrinogen could not be replaced by soluble fibrinogen or affixed albumin. It is concluded that fibrinogen, which binds to platelets upon activation or is linked to them covalently, is a recognition site for platelet-platelet interaction during aggregation.
...
PMID:Passive participation of fixed platelets in aggregation facilitated by covalently bound fibrinogen. 684 43

Pyridoxal 5'-phosphate (PALP) inhibited ADP, thrombin, adrenaline, PAF and AA induced aggregation and 14C-5HT release. Thromboxane B2 (TxB2) generation induced by all the above agents except AA was also inhibited indicating that PALP may be inhibiting AA release via phospholipase A2 activation rather than AA metabolism. PALP inhibited ristocetin induced aggregation in PRP and agglutination in formaldehyde-treated washed platelets (FWP). Inhibition of ADP, adrenaline, PAF and AA-induced aggregation and 14C-5HT release by PALP was found in resuspended platelets pretreated with PALP and sodium borohydride suggesting that inhibition was mediated by Schiff base formation with platelet surface amino groups. Irreversible fixation of PALP to the platelet membrane by borohydride reduction also inhibited thrombin induced 14C-5HT release and TxB2 generation but no thrombin induced primary aggregation or ristocetin induced agglutination in FWP. This suggests that PALP may interact with specific glycoproteins on the platelet membrane involved in ADP, adrenaline and PAF induced primary aggregation and that PALP could be inhibiting ristocetin induced agglutination by direct interaction with ristocetin or F VIII RCoF.
...
PMID:Effect of pyridoxal 5'-phosphate (PALP) on human platelet aggregation, dense granule release and thromboxane B2 generation--role of Schiff base formation. 689 Nov 7

The adherence of Candida albicans to a fibrin-platelet matrix formed in vitro was studied. Platelet-rich plasma obtained from rabbits was incubated with thrombin and CaCl2 to form a clot in tissue culture dishes. Such clots were then infected with 3 x 10(7) C. albicans cells per 0.3 ml prelabeled with [U14C]-glucose, and the percent adherence was measured after 30 min of incubation by counting the radioactivity in saline washes of the clot as well as a streptokinase-streptodornase digest of the corresponding clot. Heat- and formaldehyde-killed cells did not adhere as well as viable cells. Pretreatment of C. albicans with trypsin, chymotrypsin, and pronase reduced adherence to the clots. Normal rabbit serum and anti-Candida antiserum also inhibited adherence 40 and 100%, respectively, Diethylaminoethyl-purified anti-Candida gamma globulin (1:8) completely inhibited adherence, whereas purified normal serum gamma globulin did not. Several Candida spp. and Saccharomyces cerevisiae showed differences in their ability to adhere to clots. C. albicans and C. stellatoidea presented the highest adherence, whereas C. krusei, C. guilliermondii, and S. cerevisiae adhered less readily. Other species were intermediate in their ability to adhere.
...
PMID:Adherence of Candida albicans to a fibrin-platelet matrix formed in vitro. 699 22

The objective of the present study was to characterize the interaction between human platelets and vaccinia virus and to examine possible impairment of platelet functions. The vaccinia virus was selected for our model system because it lacks detectable neuraminidase activity. Platelets were incubated with purified viral particles labeled with 3H-thymidine and binding parameters were analyzed. Binding reached saturation with an average of 5 particles/platelet. It was not affected by the plasma but was sensitive to temperature and to metabolic inhibitors. 3H-thymidine-labeled vaccinia virus and formaldehyde-fixed platelets were used to measure viral adsorption. The adsorption was temperature-independent but was affected by ionic strength, indicating electrostatic interactions. Treatment of the fixed platelets with neuraminidase or with alkaline phosphatase reduced viral adsorption, indicating that sialate and phosphate residues on the platelet surface may be involved in the adsorption. Platelet activities were markedly affected by vaccinia virus. The virus caused a dramatic 14C-serotonin release with no added inducer. The release was inhibited by aspirin, a known inhibitor of serotonin release related to prostaglandin synthesis. Furthermore, the virus inhibited platelet aggregation, induced by either ADP, collagen, or thrombin. This study demonstrates that although vaccinia virus lacks neuraminidase activity, it does bind to platelets and affects their function.
...
PMID:Interaction between vaccinia virus and human blood platelets. 705 66

The formation of the haemostatic plug is an extremely fast process. This excludes, at least in its first phase, the involvement of soluble activating agents released from or produced by the platelets. An experiment with ADP-activated, formaldehyde-fixed platelets shows that platelets with activated fibrinogen receptors will bind inactive platelets in the presence of fibrinogen and Ca(2+)-ions. A survey of the literature shows that platelet activation is accompanied by the clustering of the fibrinogen receptors. The surface of an activated platelet, which makes part of the growing haemostatic plug therefore is covered with patches of tightly packed fibrinogen. This allows the multisite combination with the statistically distributed low affinity receptors of the newly arriving platelets. Tightly packed fibrinogen, as present on clusters of the activated GP IIb/IIIa receptors as well as when absorbed to artificial surfaces acts as an activator of platelets. Thus, the propagation of the activation process is possible without a requirement for other, external activators. Such agents, which are released from platelets and, finally, thrombin formation, are nonetheless of vital importance, not for the formation but for the consolidation of the haemostatic plug.
...
PMID:The formation of the haemostatic plug--a special case of platelet aggregation. An experiment and a survey of the literature. 823 24

We have previously demonstrated that chemically modified thrombin preparations induce endothelial cell (EC) adhesion, spreading and cytoskeletal reorganization via an Arg-Gly-Asp (RGD) sequence and the alpha v beta 3 integrin. Native thrombin, however, did not exhibit adhesive properties, consistent with crystal structure analysis, showing that Gly-Asp residues of the RGD epitope are buried within the molecule. We have now identified a possible physiological mean of converting thrombin to an adhesive protein. Plasmin, the major end product of the fibrinolytic system, converted thrombin to an adhesive protein for EC in a time and dose-dependent manner. EC adhesion and spreading was also induced by a low molecular weight (approximately 3,000 D) cleavage fragment generated upon incubation of thrombin with plasmin. Cell adhesion mediated by this fragment was completely inhibited by the synthetic peptide GRGDSP. Conversion of thrombin to an adhesive molecule was significantly enhanced in the presence of heparin or heparan sulfate, while other glycosaminoglycans (GAGs) (e.g., dermatan sulfate, keratan sulfate, chondroitin sulfate) had no effect. The role of cell surface heparan sulfate in thrombin conversion to EC adhesive protein was investigated using CHO cell mutants defective in various aspects of GAG synthesis. Incubation of both thrombin and a suboptimal amount of plasmin on the surface of formaldehyde fixed wild-type CHO-KI cells resulted in an efficient conversion of thrombin to an adhesive molecule, as indicated by subsequent induction of EC attachment. In contrast, there was no effect to incubation of thrombin and plasmin with fixed CHO mutant cells lacking both heparan sulfate and chondroitin sulfate, or with cells expressing no heparan sulfate and a three-fold increase in chondroitin sulfate. A similar gain of adhesive properties was obtained upon incubation of thrombin and plasmin in contact with native, but not heparinase-treated extracellular matrix (ECM) produced by cultured ECs. It appears that cell surface and ECM-associated heparan sulfate modulate thrombin adhesive properties through its heparin binding site in a manner that enables suboptimal amounts of plasmin to expose the RGD domain. Our results demonstrate, for the first time, a significant modulation of thrombin molecule by heparin, resulting in its conversion to a potent adhesive protein for ECs. This conversion is most effective in contact with cell surfaces, basement membranes and ECM.
...
PMID:Thrombin adhesive properties: induction by plasmin and heparan sulfate. 824 31

P-selectin (also called CD62, GMP-140, PADGEM, CD62P) is a recently described member of a family of vascular adhesion receptors expressed by activated platelets and endothelial cells that are involved in leucocyte cell adhesion. The aim of this study was to characterize a new monoclonal antibody (LYP7) directed against activated human blood platelets that inhibits ristocetin-induced platelet aggregation. Immunoadsorbent affinity chromatography and immunoprecipitation studies showed that LYP7 (IgG1) bound a surface-labelled glycoprotein (GP) which changed its apparent molecular mass (M(r)) on reduction from 138 kD (situated below GPIIb) to 148 kD (above GPIIb alpha). LYP7 and S12, a monoclonal antibody directed against P-selectin immunoprecipitated the same band. Using ELISA assay, purified P-selectin was shown to bind LYP7 and S12 monoclonal antibodies. Binding sites of 125I-labelled LYP7, which was greatly increased on thrombin-stimulated (2 U/ml) washed platelets (10825 +/- 2886, mean +/- SD) Kd = 1.5 +/- 0.5 nM) compared to resting platelets (2801 +/- 1278, mean +/- SD) (Kd = 1.5 +/- 0.6 nM), was found to be normal on thrombin-stimulated platelets taken from a patient with grey platelet syndrome or a patient with Glanzmann thrombasthenia. LYP7 (IgG1, F(ab')2 or Fab fragments) inhibited ristocetin-induced platelet aggregation of platelets in a dose-dependent fashion without affecting the binding of von Willebrand (vWf) factor. However, agglutination of formaldehyde-fixed platelets induced by ristocetin was not affected by monoclonal antibody LYP7. In addition, the binding of thrombin-activated platelets to neutrophils was inhibited by monoclonal antibody LYP7. These results strongly suggest that P-selectin, by promoting cell-cell contact, may play an active role in platelet-platelet interactions.
...
PMID:A monoclonal antibody directed against a granule membrane glycoprotein (GMP-140/PADGEM, P-selectin, CD62P) inhibits ristocetin-induced platelet aggregation. 860 15

Normal circulating platelets do not adhere to intact, undisturbed endothelium. Studies have shown, however, that platelets will adhere to virally infected or thrombin-stimulated human umbilical vein endothelial cells. Using a novel platelet/endothelial cell adhesion assay we studied the interaction of thrombin-activated platelets to human saphenous vein endothelial cells (HSVEC), and its mechanism(s). Biotinylated platelets were exposed to Hepes-Tyrode buffer, 10E5 or PAC-1 [monoclonal antibodies (Mabs) blocking GPIIb-IIIa], AK4 (Mab blocking P-selectin, 6D1 (Mab blocking vWf binding to GPIb), RGDS (small peptide blocking the fibrinogen binding site), or EDTA (dissociates GPIIb-IIIa complex) and then activated with thrombin. The platelets were subsequently exposed to thrombin-stimulated monolayer HSVEC. Phycoerythrin-streptavidin was added to the wells to fluorescently label the platelets, followed by formaldehyde fixation and washing to remove nonadherent platelets. Adhesion of platelets to HSVEC was assessed using a fluorescent multiwell plate reader. Antibodies which blocked the GPIIb-IIIa receptor and agents which competitively bound the receptor all significantly inhibited activated platelet adhesion to the activated HSVEC. We have found that thrombin significantly increases platelet/HSVEC adhesion, and this event is mediated via the integrin GPIIb-IIIa (fibrinogen receptor). These GPIIb-IIIa receptor blocking Mabs and RGDS may be useful adjuncts for improving patency following angiographic intervention and/or vein grafting in patients with high risk of thrombosis. The assay we have developed is a valuable and relatively simple method for assessing platelet/endothelial cell adhesion and activation.
...
PMID:Adhesion of activated platelets to venous endothelial cells is mediated via GPIIb/IIIa. 865 40

It has been reported that platelets stimulate generation of reactive oxygen species in neutrophils and monocytes by a mechanism that requires mutual cell-cell contact and the presence of P-selectin on the platelet surface. In the present study we investigated the effect of platelet-neutrophil contacts on neutrophil elastase secretion and phagocytic activity. Non-activated or thrombin-activated platelets were fixed with formaldehyde, washed and incubated with neutrophils in the absence or presence of various neutrophil agonists. Elastase secretion was determined by measuring the enzyme activity in cell-free supernatants using a chromogenic substrate. Platelet-neutrophil adhesion and ingestion of zymosan particles by neutrophils were quantitated by light microscopy. Platelets significantly reduced elastase secretion from neutrophils but had no effect on the elastase activity in the supernatant of neutrophil lysates. When neutrophils were stimulated with the ionophore A23187 or the chemotactic peptide FMLP, thrombin-activated platelets were more potent to inhibit elastase secretion when compared with non-activated platelets. Neutrophils that were not able to bind platelets to their surface had a significantly lower phagocytic activity when compared with neutrophil with adherent platelets or neutrophils that were incubated in the absence of platelets. The results indicate that platelet-neutrophil contacts may also lead to an inhibition of neutrophil functions and that such inhibition could be due to a transient contact rather than due to a firm platelet-neutrophil adhesion.
...
PMID:Contact-induced modulation of neutrophil elastase secretion and phagocytic activity by platelets. 873 21


<< Previous 1 2 3 4 Next >>

---