Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of a zinc metalloprotease from Serratia marcescens on platelet surface glycoproteins (GP) Ib and V was analyzed. Increasing protease treatments caused progressive loss of GP Ib with appearance of the major fragment, glycocalicin, in the supernatant solution. No GP V was detected in the supernatant solution, and protease-pretreated platelets had the same capacity as control platelets to release fragment 1 of GP V in response to thrombin. The Serratia protease-pretreated platelets did show the lag before thrombin-induced dense granule secretion, characteristic of platelets modified by pretreatment with other nonstimulating proteases. Treatment with Serratia protease gives the only demonstrated selective loss of GP Ib without apparent effect on GP V. It suggests that GP V (1) does not depend on GP Ib for its association with platelets and (2) is not the substrate for protease modification of platelet function.
 ...
PMID:Differential effect of Serratia protease on platelet surface glycoproteins Ib and V. 315 41

Platelet membrane glycoprotein V (GPV) was hydrolyzed during thrombin-induced platelet aggregation releasing a fragment GPVfl into the supernatant. Hydrolysis of GPV required catalytically active thrombin and was diminished by chemical modification of the fibrinogen binding site of thrombin. Half-maximal liberation of GPVfl occurred at a 10-fold higher concentration of thrombin than was required for half-maximal release. Time course studies at several thrombin concentrations showed disparate release of GPVfl and thrombospondin. These results emphasize the complexity of the initial events in thrombin-induced platelet activation.
 ...
PMID:Glycoprotein V hydrolysis by thrombin. Lack of correlation with secretion. 316 Dec 10

The ability of purified human gamma-thrombin to stimulate platelet function was related to its capacity to degrade GP V. Compared to alpha-thrombin, much greater amounts of gamma-thrombin were required to induce platelet aggregation; and this also applied to secretion from dense bodies, alpha-granules and lysosomal granules. Platelet stimulation by gamma-thrombin was additionally characterized by the presence of a lag-phase. Platelets with 3H-labelled surface glycoproteins showed the same functional response to both alpha- and gamma-thrombin as unlabelled platelets. But while threshold levels of alpha-thrombin induced little GP V hydrolysis confirming McGowan et al. (1), amounts of gamma-thrombin which induced substantial degradation (e.g. 8.3 nM degraded 36% of platelet GP V in 3 min) were unable to sustain either platelet aggregation or secretion. These results suggest that protein-binding regions remote from the catalytic site of alpha-thrombin are more important for platelet activation than GP V hydrolysis. They also provide further support to the argument that GP V hydrolysis may not be the essential trigger of platelet activation by thrombin.
 ...
PMID:Human gamma-thrombin: lack of correlation between a platelet functional response and glycoprotein V hydrolysis. 343 54

Bernard-Soulier syndrome (BSS) was described in 1948 as a constitutional platelet disorder characterized by giant sized platelets, a prolonged bleeding time, and a defect in prothrombin consumption. The accurate mechanisms of these abnormalities remain unexplained, especially the defect in prothrombin consumption on which we focus in this paper. Several hypotheses are proposed: firstly, a defective reaction between the platelet membrane, where the phospholipid composition is abnormal, and the proteins which initiate thromboplastin generation such as collagen, factor XI; secondly, an abnormal reaction between thrombin, whose synthesis is increased, and its receptor, possibly glycoprotein V, which is defective; lastly, as factor VIII/vW binding is diminished, an abnormal dissociation of the complex VIII/vW-VIIIc at the site of the platelet membrane, which leads to an inactivation of factor VIIIc.
 ...
PMID:The defective prothrombin consumption in Bernard-Soulier syndrome. Hypotheses from 1948 to 1982. 622 3

Platelet membrane glycoprotein V ( GPV ) is hydrolyzed during thrombin-induced platelet aggregation. The present studies were undertaken to determine whether cleavage of GPV was a direct result of thrombin action or was secondary to platelet activation. Acetylsalicylic acid or vincristine had little or no effect on platelet activation or cleavage of GPV by thrombin. Prostacyclin or antimycin A and 2-deoxyglucose inhibited platelet activation but had no effect on hydrolysis of GPV . These findings suggest that the hydrolysis of GPV occurs independently of the biochemical and morphological changes associated with platelet activation and is therefore a direct effect of thrombin.
 ...
PMID:The effect of platelet inhibitors on glycoprotein V hydrolysis by thrombin. 623 49

To assess the possibility that hydrolysis of the platelet surface thrombin substrate, glycoprotein V, is a necessary step in thrombin-induced platelet activation, thrombin-catalyzed hydrolysis of glycoprotein V was correlated with thrombin-induced platelet activation. Hydrolysis of tritium-labeled glycoprotein V on washed human platelets was measured by the appearance of a labeled supernatant fragment, and platelet activation was measured as secretion of ATP. Hydrolysis of glycoprotein V was linear with respect to both thrombin concentration and time of incubation. The extent of platelet activation was correlated with the rate of hydrolysis but not with the amount hydrolyzed. Maximum platelet activation could be obtained with thrombin treatments resulting in hydrolysis of as little as 4% of glycoprotein V per min. Glycoprotein V was partially removed from platelets by pretreatment with either platelet calcium-dependent protease or chymotrypsin. The rate of thrombin-catalyzed hydrolysis of the remaining glycoprotein V from these pretreated platelets was as little as 1.5% the rate from control platelets, but there was no impairment of the extent of platelet activation. Thus, these protease-pretreated platelets compared with control platelets showed a different correlation of glycoprotein V hydrolysis with platelet activation. Glycoprotein V was also partially removed by pretreatment of prostacyclin-inhibited platelets with thrombin. After removal of thrombin and prostacyclin, these platelets were desensitized to subsequent activation by thrombin. Incubation of desensitized platelets with nonsaturating levels of thrombin led to less than 25% of the activation seen with control platelets but to a slightly greater hydrolysis of glycoprotein V. Thus, the desensitization to thrombin was not due to loss of ability of the activating thrombin to hydrolyze glycoprotein V. These results do not exclude a role for glycoprotein V as a component of the platelet thrombin receptor, but they indicate that there is no simple relationship between thrombin-induced hydrolysis of glycoprotein V and platelet activation.
 ...
PMID:Correlation of thrombin-induced glycoprotein V hydrolysis and platelet activation. 630 38

The action of exogenous calcium-dependent protease (CDP) on tritium-labeled surface glycoproteins was analyzed by incubation of labeled, washed human platelets with CDP partially purified from human platelets. Labeled glycoproteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by fluorography. Incubation of the labeled platelets with the protease led to a loss (calcium-dependent) from the platelets of glycoproteins Ib and V and concomitant appearance in the supernatant solution of glycocalicin (a proteolytic fragment of glycoprotein Ib), glycoprotein V, and other, unidentified glycoproteins. These changes in surface label were accompanied by alterations in three parameters of platelet function. Compared to control platelets, the CDP-treated platelets were activated by thrombin more slowly and showed less saturable and nonsaturable binding of thrombin. The CDP-treated platelets, but not the controls, aggregated on addition of fibrinogen, indicating that treatment with CDP had exposed fibrinogen receptors. The alterations in surface glycoproteins and functional parameters were compared over a 1000-fold range of CDP treatment. The decreased binding of thrombin and the exposure of fibrinogen receptors were correlated with the release of surface glycoproteins to the supernatant solution, but the slow activation by thrombin was observed under conditions where no release of labeled glycoproteins was detected (i.e., brief incubations with low concentrations of CDP). Activation of the endogenous CDP with 2.5 mM calcium chloride plus the ionophore A23187 was accompanied by hydrolysis of actin-binding protein, a known substrate, and release to the supernatant solution of labeled glycocalicin and glycoprotein V plus a faster-migrating glycoprotein not released by exogenous protease. This effect was observed in the presence of leupeptin, which completely inhibited action of exogenous protease, suggesting that platelet calcium-dependent protease may modify the platelet surface in ways that can cause alterations of platelet function.
 ...
PMID:The action of calcium-dependent protease on platelet surface glycoproteins. 631 9

Treatment of human platelets with alpha-thrombin leads to the selective hydrolysis of only one membrane protein, glycoprotein V. To determine whether glycoprotein V was directly cleaved by alpha-thrombin and to permit further characterization of this glycoprotein as the potential functional thrombin receptor, glycoprotein V was purified to > 98% homogeneity. Washed platelets were prepared from concentrates within 18 h of venipuncture, since clinically expired platelets (> 72 h from venipuncture) were shown to contain little or no detectable glycoprotein V. Glycoprotein V was eluted from the platelet membrane by equilibrating the platelets (4 X 10(9)/ml) at 37 degrees C for 24 h in 0.01 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (Hepes), pH 7.6 (1 mM in EDTA, 0.3 M in NaCl). Purification was achieved by initially performing ammonium sulfate fractionation, followed by chromatography on Sephacryl S-200, hydroxylapatite, and DEAE- and CM-cellulose, and yielded 0.5 to 1.0 mg of purified glycoprotein per 100 units of platelet concentrate (approximately 6 X 10(12) platelets). Purified glycoprotein V (Mr = 82,000) was a thrombin substrate, and on hydrolysis yielded a major fragment, GPVf1 (Mr = 69,500), identical in molecular weight with that observed previously in the supernatant of thrombin-treated, periodate-labeled platelets. Glycoprotein V existed as at least eight distinct isoelectric forms with pI values ranging from 5.85 +/- 0.05 to 6.55 +/- 0.05. The purified glycoprotein contained approximately 48% carbohydrate by weight, consisting of neutral hexose, hexosamine, and sialic acid in a molar ratio of approximately 8:2:1. Rabbit antiglycoprotein V antibody gave a single precipitin line against purified glycoprotein V, which showed a line of complete identity with Triton-solubilized washed platelets. The availability of purified glycoprotein V and antiglycoprotein V antibody will be useful in delineating the role of this glycoprotein in thrombin activation of platelets.
 ...
PMID:Purification and preliminary physicochemical characterization of human platelet membrane glycoprotein V. 677 67

In the early phase of primary hemostasis, platelets adhere to damaged vessel wall by binding via the platelet glycoprotein (GP) Ib-V-IX complex to von Willebrand factor (vWf) exposed on the subendothelium. The complex is composed of four glycoprotein subunits, GPIb alpha, GPIb beta, GPIX and GPV, each with a variable number of leucine-rich repeats. GPIb alpha and GPIb beta are linked by a disulphide bridge while GPIX and GPV associate noncovalently with the complex. The study of defects in the expression of the GPIb-V-IX complex at the platelet surface leading to pathological disorders, like Bernard-Soulier syndrome (BSS), or in the affinity of platelets for vWf, like pseudo-von Willebrand disease, has helped to delineate the binding site for vWf on GPIb alpha. However, the mechanism by which the complex binds to vWf has not yet been elucidated but it must involve changes in the conformation of the molecules as no interaction between platelets and vWf occurs in the plasma. The GPIb-V-IX complex has a binding site for thrombin on GPIb alpha which participates in the platelet activation by that agonist. GPV is also cleaved by thrombin but the function of this proteolysis is not clear. The platelet response to thrombin is slower and weaker when the thrombin binding site on GPIb alpha is blocked or cleaved or when the GPIb-V-IX complex is not expressed on the platelet surface as in classic BSS. At low doses of thrombin, the rapid activation of the platelets via the seven-transmembrane thrombin receptor is dependent on the presence of the GPIb-V-IX complex.
 ...
PMID:Platelet GPIb-V-IX complex. Structure, function, physiology, and pathology. 766 Jan 35

Human platelet glycoprotein (GP) V (M(r) 83,300), whose primary structure is reported here, is a part of the Ib-V-IX system of surface glycoproteins (GPs Ib alpha, Ib beta, V, IX) that constitute the receptor for von Willebrand factor (vWf) and mediate the adhesion of platelets to injured vascular surfaces in the arterial circulation, a critical initiating event in hemostasis. System members share physical associations, leucine-rich glycoprotein (LRG) structures, and a congenital deficiency state, Bernard-Soulier syndrome. With PCR techniques and platelet cDNA templates, 1.4 kb of GP V cDNA sequence was obtained that encodes 469 GP V amino acids. A genomic 3.5-kb BamHI fragment was then isolated that includes 3.46 kb of GP V cDNA sequence: the 1.7-kb open reading frame plus 2 bases of the 5' and 1.8 kb of the 3' untranslated regions. Northern blot analysis reveals three GP V platelet transcripts of 3.8, 4.2, and 5.2 kb. A 16-amino acid signal peptide is present. Mature GP V is a 544-amino acid transmembrane protein with a 504-amino acid extracellular domain that encompasses a set of 15 tandem LRG repeats in a "flank-LRG center-flank" array [Roth, G. J. (1991) Blood 77, 5-19] along with eight putative N-linked glycosylation sites and cleavage sites for thrombin and calpain. GP V is a transmembrane, adhesive LRG protein that plays an undefined, but potentially critical, role in the expression and/or function of the Ib-V-IX receptor for vWf/shear-dependent platelet adhesion in arteries.
 ...
PMID:Human platelet glycoprotein V: characterization of the polypeptide and the related Ib-V-IX receptor system of adhesive, leucine-rich glycoproteins. 769 Sep 59


<< Previous 1 2 3 4 5 6 7 Next >>