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)

Prostaglandin endoperoxides produced during aggregation of blood platelets are potent promoters of platelet aggregation and the release reaction. The present investigation has studied the effects of prostaglandin endoperoxides produced by platelet microsomes after incubation with arachidonic acid on the ultrastructure of platelets. Prostaglandin endoperoxides caused platelet pseudopod formation and internal transformation associated with a contractile wave within the platelet. The contractile process was similar to that seen following incubation of platelets with collagen or thrombin but was more complete than that seen with 25 muM ADP. Platelet aggregation was more prominent in unstirred samples incubated with the prostaglandin endoperoxides than in samples similarly incubated with 25 muM ADP. Dilatation of the open canalicular system was not a prominent feature except at 45 minutes after addition of the endoperoxides to the platelets, when the platelets appeared to be in a recovery phase. We conclude that the endoperoxides promote platelet stickiness and platelet aggregation by directly or indirectly stimulating the platelet contractile system.
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PMID:The influence of prostaglandin endoperoxides on platelet ultrastructure. 16 97

Exogenous arachidonate addition to intact platelets, in the absence or the presence of blood vessel microsomes, results in the production of thromboxane B(2) (the stable degradation product of thromboxane A(2)) only. Prostaglandin (PG) endoperoxides are released from intact platelets only when thromboxane synthetase is inhibited. Thus, addition of exogenous arachidonate to imidazole-pretreated platelets in the presence of bovine aorta microsomes (source of prostacyclin synthetase) results predominantly in the synthesis of 6-keto-PGF(1alpha) (the stable degradation product of prostacyclin). Strips of intact aorta were removed from aspirin-treated rabbits, thus the isolated blood vessels were unable to convert endogenous or exogenous arachidonate to prostacyclin. Human platelets, with [(14)C]arachidonate-labeled phospholipids, adhered to the blood vessel segments and released some thromboxane B(2). The subsequent addition of thrombin facilitated the release of endogenous arachidonate and thromboxane, but no labeled 6-keto-PGF(1alpha) was detectable. There is therefore no direct chemical evidence of PG-endoperoxide release from human platelets during either aggregation or adhesion, which therefore precludes the possibility that blood vessels use platelet PG-endoperoxide for prostacyclin synthesis. Imidazole inhibited the thromboxane synthetase in the labeled platelets, and thereafter thrombin stimulation resulted in the release of platelet-derived, labeled PG-endoperoxides that were converted to labeled prostacyclin by the vascular prostacyclin synthetase. The latter result suggests a potential antithrombotic therapeutic benefit might be achieved using an effective thromboxane synthetase inhibitor.
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PMID:Platelet and blood vessel arachidonate metabolism and interactions. 37 40

Pregnancy termination by the intraamniotic injection of hypertonic saline may result in coagulation defects. This complication seems to be uncommon with prostaglandins. The present study was designed to elucidate any possible effects of prostaglandin administration on coagulation parameters in patients with fetal death in utero. Labour was induced in 20 cases of intrauterine fetal death by either intravenous (11) or intramuscular (9) administration of Sulprostone. Normotest, thrombin clotting time, ethanol fractionation, fibrinogen level and platelet count were obtained in each patient prior to and immediately after drug administration. Although retention of the fetus for as long as 84 days was recorded (mean 14 days), no patient presented with abnormal clotting parameters. Prostaglandin induction was successful in all 20 cases. After explosion of the fetus, coagulation parameters were not significantly different from pretreatment values. Estimated blood loss never exceeded 500 cc. It is concluded that intramuscular or intravenous administration of Sulprostone for induction of labour in fetal death in utero does not affect the clotting system nor trigger off disseminated intravascular coagulation.
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PMID:[Blood coagulation parameters in prostaglandin-induced labour after intrauterine fetal death (author's transl)]. 67 15

Oligomycin, antimycin, and 2,4-dinitrophenol, compounds that are known to inhibit oxidative phosphorylation by different mechanisms, inhibit the production of prostaglandins by serum-stimulated MC5-5 cells. The prostaglandin production that is stimulated by thrombin and bradykinin is inhibited by 2,4-dinitrophenol. Prostaglandin synthesis by MC5-5 cells from exogeneously-supplied arachidonic acid, however, is not affected by 2,4-dinitrophenol. Antimycin and 2,4-dinitrophenol also inhibit the serum-stimulated release of arachidonic acid from the cellular lipids, suggesting that it is the expression of phospholipase activity, a prerequisite for synthesis of prostaglandins by MC5-5 cells, that is dependent on oxidative phosphorylation.
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PMID:Prostaglandin production by methylcholanthrene-transformed mouse BALB/3T3: effect of oxidative phosphorylation inhibitors. 84 Nov 8

Material causing contraction of the isolated rabbit aorta (rabbit aorta contracting substance, RCS) was released from guinea pig lung following perfusion with arachidonic acid and from human blood platelets after addition of thrombin to induce aggregation. Prostaglandin endoperoxides (prostaglandins G2 and/or H2) were found both in the perfusate of guinea pig lung (1-3 ng/ml) and in the medium collected after platelet aggregation (13-37 ng/ml). The contractile response of the isolated rabbit aorta to the pure prostaglandins G2 and H2 was also determined. These data combined with the quantitative analyses of the endoperoxides released from the lungs and platelets showed that only a minor part of the rabbit aorta contracting activity was due to the prostaglandin endoperoxides. The major part of the activity consisted of very unstable material. The half life of this material was about 30 s at 37 degrees whereas at this temperature the prostaglandin endoperoxides had a half life of about 5 min.
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PMID:Prostaglandin endoperoxides IX. Characterization of rabbit aorta contracting substance (RCS) from guinea pig lung and human platelets. 115 78

Prostaglandin endoperoxide synthase (PES, EC 1.14.99.1) catalyse the conversion of arachidonic acid into prostaglandin H2. The enzyme is a 140 kDa homodimer which contains both a cyclo-oxygenase activity (converting arachidonate into prostaglandin G2) and peroxidase activity (reducing prostaglandin G2 to H2). PES undergoes rapid self-inactivation during oxygenation of arachidonate to prostaglandin H2 in vitro. The previously reported cDNA-derived amino acid sequence indicates numerous sites for trypsin or thrombin cleavage. Most of these sites must be inaccessible, since these enzymes cleave only at Arg253. The enzyme appears to be a self-adherent and highly folded molecule, since after cleavage it retains its functional assembly and its homodimer size of 140 kDa, as well as its overall enzymic activity. Only under denaturing conditions (e.g. SDS/PAGE) can the proteolytic peptides be demonstrated: a 38 kDa C-terminal fragment containing the aspirin-derived-acetyl-binding ability, and a 33 kDa N-terminal fragment. In the present studies we investigated whether the two enzymic activities of PES can be differentially manipulated by proteolytic cleavage or by substrate (arachidonate) self-inactivation. The results indicated that, during arachidonate oxygenation by PES, the cyclooxygenase activity is selectively inactivated, whereas the peroxidase activity is essentially retained. By contrast, thrombin or trypsin cleavage of pure PES or microsomal PES (to yield the 38 and 33 kDa peptide fragments) inactivated the peroxidase, but not the cyclo-oxygenase. Taken together, these results suggest the presence of separate cyclo-oxygenase and peroxidase structural domains on the enzyme.
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PMID:Differential modification of cyclo-oxygenase and peroxidase activities of prostaglandin endoperoxidase synthase by proteolytic digestion and hydroperoxides. 211 18

Prostaglandin synthesis in endothelial cells may be initiated by the addition of exogenous substrate (arachidonic acid) or by addition of thrombin or the CA2+-ionophore A23187, which leads to prostacyclin formation from endogenous substrates. We noticed that endothelial cells produce more than twice the amount of prostacyclin when incubated with thrombin and arachidonic acid together than with arachidonic acid alone. In addition, it was found that the thrombin-induced conversion of endogenous substrates was inhibited by exogenous arachidonic acid. This means that the conversion of exogenous added arachidonic acid to prostacyclin was stimulated by thrombin. This activation of the enzymes involved in prostacyclin synthesis lasted about 5 min and could be inhibited by phospholipase inhibitors such as mepacrine and p-bromophenyl-acylbromide but not by the cAMP analogue dibutyryl cAMP, an inhibitor of arachidonic acid release from cellular phospholipids. These data demonstrate that, in addition to causing release of endogenous substrate, thrombin and the Ca2+-ionophore also activate the enzyme system involved in the further transformation of arachidonic acid.
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PMID:The role of thrombin in the regulation of the endothelial prostaglandin production. 299 48

The activity of partially purified phospholipase C from human platelets was totally dependent on Ca2+, and approximately 800 microM Ca2+ was required for half-maximal activity. The enzyme hydrolyzed endogenous substrates in the order DPI greater than TPI greater than PI in a Ca2+-dependent manner. Hydrolysis of TPI in thrombin-stimulated platelets was dependent on the amount of the agonist, and it was not affected by the presence or absence of extracellular Ca2+. Hydrolysis was inhibited by preincubation with Quin-2AM in the absence of extracellular Ca2+. The intracellular Ca2+ concentration was significantly lowered below the basal level by such treatment. These observations suggested that TPI breakdown in thrombin-stimulated platelets is mediated by agonist-receptor coupling and requires at least the basal level of intracellular Ca2+.
Adv Prostaglandin Thromboxane Leukot Res 1985
PMID:Ca2+ requirement in hydrolysis of phosphatidylinositol-4,5-bisphosphate in human platelets. 300 31

Prostaglandin (PG) H synthase and eicosanoid products of arachidonic acid metabolism have been implicated in several steps in the carcinogenic process. This study assessed these parameters using primary cultures of human urothelial cells. To determine the possible presence of permeability barriers to agonist stimulation, incubations were performed with adherent cells in the presence or absence of thioglycolate pretreatment or with cell suspensions. No evidence for permeability barriers was observed. With adherent cells in the absence of thioglycolate, radioimmunoassayable PGE2 was stimulated by epinephrine less than 12-O-tetradecanoylphorbol-13-acetate = thrombin less than bradykinin = A23187 much less than arachidonic acid. Tumor promoters but not non-tumor promoters stimulated PGE2 synthesis. 1-Oleoyl-2-acetylglycerol which like 12-O-tetradecanoylphorbol-13-acetate activates protein kinase C also increased PGE2 synthesis. Cells prelabeled with [14C]arachidonic acid were exposed to agonists and the profile of eicosanoids synthesized was assessed by high performance liquid chromatography. With bradykinin, the pattern of eicosanoids synthesized was 6-keto-PGE1 alpha (12% of total 14C label), thromboxane B2 (0.4%), PGF2 alpha (1.7%), PGE2 (18%), PGD2 (1%), leukotrienes (0.4 to 1%), 12-hydroxy-5,8,10-heptadecatrienoic acid (3%), 15-hydroxy-5,8,11,13-eicosatetraenoic acid (4%), 12-hydroxy-5,8,10,14-eicosatetraenoic acid (0%) and 5-hydroxy-5,8,12,14-eicosatetraenoic acid (2%). Thus, human urothelial cells contain both prostaglandin H synthase and lipoxygenase pathways with the former being more prominent. These pathways may participate in urinary bladder carcinogenesis.
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PMID:Eicosanoid synthesis by cultured human urothelial cells: potential role in bladder cancer. 309 68

N-Ethylmaleimide dose dependently inhibited platelet aggregation induced by collagen or arachidonate but did not inhibit the aggregation by thrombin or ionophore A23187 within the concentrations tested. [3H]Arachidonate release from membrane phospholipids of the collagen-stimulated platelets was inhibited by N-ethylmaleimide in parallel with the inhibition of aggregation, but not in response to A23187. N-Ethylmaleimide prevented 45Ca2+ influx into platelet cells from outer medium induced by collagen, and also inhibited the increase in the concentration of cytoplasmic free Ca2+, which probably results from Ca2+ influx, as monitored by quin2 fluorescence, under stimulation with arachidonate. The concentration of N-ethylmaleimide giving a complete inhibition of Ca2+ influx was consistent with that required to inhibit collagen- or arachidonate-induced aggregation. Prostaglandin metabolism from arachidonate to thromboxane A2 was not disturbed by N-ethylmaleimide, while phosphatidate formation induced by arachidonate was slightly inhibited by it at concentrations at which aggregation was completely inhibited. These data suggest that N-ethylmaleimide preferentially suppresses increase in cytoplasmic free Ca2+ which is linked to thromboxane A2-receptor occupation in collagen- or arachidonate-stimulated platelets, probably due to blockage of Ca2+ influx through Ca2+-channel protein, thereby inhibiting aggregation induced by these agonists.
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PMID:N-ethylmaleimide inhibits Ca2+ influx induced by collagen or arachidonate on rabbit platelets. 310 97


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