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)

We describe a functional assay for protein C in human plasma samples based on the ability of activated protein C to prolong the kaolin-cephalin activated partial thromboplastin time of normal plasma. Protein C is separated from its inhibitor by elution of a barium citrate precipitate, and activated by incubation with human alpha-thrombin for one hour. Thrombin is then inhibited by antithrombin III and heparin, heparin neutralized by protamine sulfate, and protein C activity measured in the partial thromboplastin time. 24 normal subjects had a mean protein C level of 94 +/- 12% (SD) of the activity in pooled normal plasma. Seven patients with severe liver disease had a mean protein C of 28%. Eleven patients with disseminated intravascular coagulation had a mean protein C of 29%. Eight patients receiving warfarin therapy had a mean protein C of 17%. The assay is relatively simple and should be suitable for general laboratory use.
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PMID:A functional assay for protein C in human plasma. 668 83

Factor Xa binds to a receptor available on the platelet surface after the release reaction. The receptor consists of phospholipid and factor V. Factor Xa bound to the receptor catalyses the activation of prothrombin effectively. The effects of bovine protein C, a vitamin-K-dependent zymogen of a serine protease, on prothrombin activation by platelet-bound bovine factor Xa has been studied. Protein C was found to be activated (protein Ca) by thrombin formed in the prothrombin-platelet-factor Xa incubation. Protein Ca in contrast to the zymogen, protein C, or protein Ca inactivated with diisopropylphosphofluoridate inhibited prothrombin activation by factor Xa in the presence of platelets. protein Ca was found to destroy the receptor by proteolysis whereas direct binding of protein Ca to the receptor could not be demonstrated. The inhibition by protein Ca could be monitored as a parallel decrease in factor Xa binding and prothrombin activation. The receptor was protected by factor Xa from proteolysis by protein Ca. Protein Ca was also found to inhibit the interaction between prothrombin and the factor Xa platelet receptor. These results indicate that protein C after activation may have a role as a regulator of prothrombin activation in vivo.
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PMID:Inhibitory effect of activated protein C on activation of prothrombin by platelet-bound factor Xa. 689 81

Thrombin-catalyzed activation of Protein C is accelerated by a human endothelial cell surface cofactor. The cofactor occurs also on mouse hemangioma cells (a transformed endothelial cell line), but not on cultured human smooth muscle cells or fibroblasts. The cofactor remains bound to the cell surface during Protein C activation. The cofactor is saturable with respect to both Protein C (Km = 0.72 +/- 0.07 microM) and thrombin (Km = 0.48 +/- 0.05 nM). Diisopropylphosphoryl-thrombin is a competitive inhibitor of the cofactor-dependent reaction with Ki = 0.56 +/- 0.1 nM. Prothrombin Fragment 1, the peptide derived from prothrombin that retains phospholipid binding capacity, does not inhibit activation of Protein C when present in a 7:1 molar excess over Protein C. Platelet Factor 4 (20 microgram/ml) also fails to inhibit Protein C activation. It is concluded that the endothelial cell provides a surface on which Protein C can be activated under physiological conditions.
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PMID:Functional properties of an endothelial cell cofactor for thrombin-catalyzed activation of protein C. 689 92

Protein C is a precursor of plasma serine proteinases, and its active form inactivates specifically blood coagulation Factor V and Factor VIII. Since a specific and sensitive synthetic substrate for the activated protein C was not known, we studied its amidolytic activity toward 25 fluorogenic peptides of the type peptidyl-4-methylcoumaryl-7-amide (peptidyl MCA). The activated protein C, namely, bovine protein C activated by bovine alpha-thrombin, showed the highest activity toward Boc-Leu-Ser-Thr-Arg-MCA. The enzyme's Km and Kcat values for this substrate were calculated to be 3.3 x 10(-4) M and 8.4 s-1, respectively. Optimum conditions for measurement of activated protein C activity were studied with this substrate. Optimum pH was 8.5. For the maximum activity at pH 8.5, concentrations of 0.1 M NaCl and 1 mM CaCl2 had to be maintained in the reaction mixture. The fluorogenic peptide Boc-Leu-Ser-Thr-Arg-MCA was successfully applied to a simple and accurate assay of protein C during its purification.
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PMID:A new fluorogenic peptide substrate for vitamin K-dependent blood coagulation factor, bovine protein C. 689 48

Activated protein C is a potent anticoagulant and profibrinolytic enzyme that can be derived from the vitamin-K-dependent serine protease zymogen, protein C, by the action of thrombin. Protein C antigen concentration was determined in plasmas from normals (n = 40) and from 38 patients with intravascular coagulation as evidenced by positive FDP (greater than micrograms/ml). Plasma protein C was 4 micrograms/ml in normals and was significantly depressed (less than 2 SD below the mean of normals) in 19 of the 38 patients. Of 15 patients with suspected intravascular coagulation but normal FDP, protein C was decreased in 5 individuals; 3 of these 5 patients had liver disease. Based on these results, we suggest that extensive activation of the coagulation system in vivo causes a significant consumption of protein C, presumably due to its activation by thrombin and subsequent clearance.
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PMID:Protein C, an antithrombotic protein, is reduced in hospitalized patients with intravascular coagulation. 689 90

The purpose of this study was to clarify differences in coagulation and fibrinolytic activation between the various subtypes and phases of ischaemic stroke. Haemostatic activation markers were measured in 52 patients with cardioembolic stroke, 32 with atherothrombotic stroke and 54 with lacunar stroke and compared with 23 age-matched controls. Data were obtained in the acute (< or = 7 days after onset), subacute (8-28 days) and chronic (> or = 29 days) phases of stroke. In patients with cardioembolic stroke, D-dimer and alpha 2-antiplasmin-plasmin complex levels were higher during the acute and subacute phases, while thrombin-antithrombin III complex levels were higher during the acute phase than in patients with lacunar stroke and controls. In cardioembolic stroke, fibrinopeptide A was increased during the acute and subacute phases, thrombin-antithrombin III complexes were higher during the subacute phase and D-dimer levels were higher during the chronic phase. Protein C activity was lower during the acute phase than in atherothrombotic stroke, lacunar stroke and controls. Protein C antigen was lower during the acute phase than in lacunar stroke and controls and during the chronic phase than in lacunar stroke. In contrast, only D-dimer levels were higher in atherothrombotic stroke patients than controls during the acute and chronic phases and no significant alterations in these markers were observed in the patients with lacunar stroke. These findings suggest that measurement of molecular markers of coagulation and fibrinolysis may be useful for detecting intracardiac thrombin and plasmin generation in patients with cardioembolic stroke.
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PMID:Alterations of haemostatic markers in various subtypes and phases of stroke. 750 62

Thirty consecutive children scheduled for pediatric cardiac operation with cardiopulmonary bypass were included in the study. Before the operation, the patients were randomly divided into two groups: with aprotinin (n = 15, 30,000 U/kg after induction of anesthesia, 30,000 U/kg added to the prime of the cardiopulmonary bypass or without aprotinin (n = 15). Thrombomodulin, (free) protein S, protein C, and thrombin/antithrombin III complex were measured from arterial blood samples taken after induction of anesthesia (at baseline, before aprotinin) and before, during, and after cardiopulmonary bypass until the first postoperative day. Standard coagulation parameters (antithrombin III, fibrinogen, platelet count, and partial thromboplastin time) were without differences between the groups. Thrombomodulin plasma concentrations were within normal range ( < 40 micrograms/L) and were similar in both groups at baseline. During cardiopulmonary bypass and until 5 hours after cardiopulmonary bypass, however, thrombomodulin plasma levels were significantly lower in the children treated with aprotinin. No further differences were observed on the first postoperative day. Protein C and protein S plasma levels did not differ between the two groups. Thrombin/antithrombin III-complex plasma concentrations increased significantly during cardiopulmonary bypass, however, without showing differences between children with (225 +/- 49 micrograms/L) and without (149 +/- 31 micrograms/L) aprotinin treatment. Blood loss and the need for homologous blood and blood products did not differ significantly between the two groups. We concluded that administration of aprotinin resulted in reduced thrombomodulin plasma levels in pediatric patients undergoing cardiac operation without altering protein C/protein S plasma concentration. The exact role of aprotinin in endothelium-derived coagulation should be further studied.
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PMID:Influence of aprotinin on the thrombomodulin/protein C system in pediatric cardiac operations. 751 76

Aprotinin has been reported to reduce bleeding in cardiac surgery patients. Its mechanisms of action on coagulation have not been fully elucidated. In a prospectively randomized study of 40 patients undergoing elective aortocoronary bypass grafting, the influence of high-dose aprotinin (2 million IU of aprotinin before CPB, 500,000 IU/h until the end of operation, 2 million IU added to the prime) (N = 20) on endothelial-related coagulation was compared to a nontreated control group (N = 20). Thrombomodulin (TM), protein C and (free) protein S as well as thrombin/antithrombin-III (TAT) plasma concentrations were measured by enzyme-linked immunosorbent assays (ELISA) before the aprotinin infusion, before cardiopulmonary bypass (CPB), during CPB and after CPB, at the end of surgery, 5 hours after CPB, and on the first postoperative day. All standard coagulation parameters (AT-III and fibrinogen plasma levels, platelet count, partial thromboplastin time) did not differ between the two groups. At baseline, TM plasma levels were within the normal range (< 40 ng/mL) and similar in both groups. During CPB, TM plasma concentrations decreased similarly in both groups (aprotinin: 18 +/- 6 ng/mL, control: 17 +/- 7 ng/mL) followed by a comparable increase in the postbypass period until the first postoperative day (aprotinin: 60 +/- 10 ng/mL, control: 53 +/- 11 ng/mL). Protein C and (free) protein S plasma levels also showed no differences between the two groups. On the first postoperative day, baseline values for protein C and protein S had not yet been reached.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Does aprotinin influence endothelial-associated coagulation in cardiac surgery? 752 60

Protein C (PC) is a vitamin K-dependent zymogen that inactivates factors Va and VIIIa after its activation by thrombin complexed to thrombomodulin. We characterized a monoclonal antibody (mAb) against PC, whose only influence on PC functions was to inhibit PC activation by the thrombin-thrombomodulin complex. It recognized an epitope in the PC heavy chain, the conformation of which is calcium-dependent. The mAb did not recognize a natural PC variant that was not activated by the thrombin-thrombomodulin complex (mutation R229Q) and did recognize a synthetic peptide corresponding to PC amino acids 225-235 in an Elisa assay. The peptide inhibited PC activation by the thrombin-thrombomodulin complex. These data confirm that the calcium-binding loop of the serine-protease domain is involved in the interaction of PC with the thrombin-thrombomodulin complex.
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PMID:Amino acids 225-235** of the protein C serine-protease domain are important for the interaction with the thrombin-thrombomodulin complex. 754 Sep 90

The relevance of coagulation abnormalities in ischemic stroke remains uncertain. The purpose of this study was to identify abnormal patterns of coagulation in established ischemic stroke. We measured coagulation parameters in 86 patients with acute ischemic stroke: 10 lacunar, 55 atherothrombotic and 21 cardioembolic. Statistical comparisons were made between different stroke groups and between all stroke patients and 60 healthy controls. A decrease in functional antithrombin III and plasminogen and an increase in thrombin-antithrombin III complexes, total protein S, tissue plasminogen activator, plasminogen activator inhibitor and D-dimer were observed in the stroke group (p < 0.05). A positive correlation was found between tissue plasminogen activator and thrombin-antithrombin III levels in cardioembolic stroke (p < 0.05). Protein C levels showed significant differences between the three groups, and in the cardioembolic group they were lower than in controls (p < 0.05). Antiphospholipid antibodies were positive in two cases. We conclude that activation of coagulation and fibrinolytic pathways was observed during the acute phase of ischemic stroke. Protein C activity is different in the three types of strokes analyzed, and higher levels seem to be associated with lacunar lesions. Antiphospholipid antibodies do not seem to play an important role in the pathogenesis of stroke in a nonselected population.
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PMID:Hemostatic disturbances in acute ischemic stroke: a study of 86 patients. 765 7


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