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:3.4.21.6 (thromboplastin)
13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Blanket serial controls are not necessary in low-dosage heparin treatment. It would, in any case, be difficult under normal clinical conditions and would run counter to the whole conception of low-dose heparin treatment. However, in problem cases with an increased thrombo-embolic risk, sensitive methods for monitoring the heparin effect are recommended. A study on 150 patients has indicated that the most sensitive method is the use of chromogenic substrates. Thrombin time, using low-concentration thrombin solution of 1.5 NIH units/ml, thrombelastogram and activated partial thromboplastin time are less sensitive. Antithrombin III levels should be determined in all cases of increased heparin tolerance. With reduced antithrombin III levels and higher body weight an increase of the standard dose from 5000 U.S.P. units heparin t. i. d. subcutaneously to 7500 U.S.P. units t. i. d. should be considered.
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PMID:[Does low-dosage heparin treatment require serial haematological controls? (author's transl)]. 47 60

The inactivation of thrombin and factor Xa by antithrombin was determined in the presence of heparin fractions of different molecular weights and with high affinity for antithrombin. The ability to potentiate the inactivation of either coagulation factor increased with increasing length of the polysaccharide chain.
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PMID:On the molecular-weight-dependence of the anticoagulant activity of heparin. 48 55

Factor V (Va) is essential for binding of factor Xa to the surface of platelets. After thrombin treatment, normal platelets release at least five times more factor Va activity than is required for maximal factor Xa binding. The concentration of factor V activity obtained after thrombin stimulation of 10(7) normal platelets is sufficient to allow half-maximal factor Xa binding to 10(8) platelets (10% normal, 90% factor-V deficient). Therefore, factor Va activity is not limiting in platelet-surface factor Xa binding and prothrombin activation in normal platelets; some other components limit the number of binding sites. We report studies of a patient (M.S.) with a moderate to severe bleeding abnormality whose platelets are deficient in the platelet-surface component required for the factor Va-factor Xa binding. The patient's platelet factor Va activity released after thrombin treatment is normal, but factor Xa binding is 20%-25% of control values at saturation. Abnormal prothrombin consumption in a patient with normal plasma coagulation factors and platelet function suggests a disorder in platelet-surface thrombin formation.
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PMID:Deficiency of factor Xa-factor Va binding sites on the platelets of a patient with a bleeding disorder. 49 93

The precise quantitation of activated factors in human factor IX concentrates has been accomplished with the use of recently developed, specific assays for factors IXa, Xa, and thrombin. The assay for factor IXa, which measures the initial rate of 3H-factor-X activation, was shown to be specific for factor IXa in the concentrates. Activated factor IX concentrates contained 1.0-2.3 microgram/ml of factor IXa; whereas the assays of unactivated concentrates were negative (less than 0.2 microgram/ml). The assays of factor Xa and thrombin, which measure the initial rate of p-nitroaniline release from S-2222 and S-2238, respectively, showed similar small amounts of factor Xa (4-34 ng/ml) and thrombin (12-76 ng/ml) in the activated and unactivated concentrates. The nonactivated partial thromboplastin time of the concentrates correlated significantly with the factor IXa content, but not with factor Xa or thrombin. Antithrombin III antigen in 3 of 4 concentrates was several-fold higher than antithrombin III activity, suggesting the presence of antithrombin III complexed with activated factors. These results support the hypothesis that the degree of activation of factor IX concentrates is related primarily to the concentration of factor IXa, which may be responsible for the thrombogenicity of these concentrates in some clinical settings.
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PMID:Activated clotting factors in factor IX concentrates. 49 95

The rates of prothrombin activation under initial conditions of invariant concentrations of prothrombin and Factor Xa were studied in the presence of various combinations of Ca2+, homogeneous bovine Factor V, Factor Va, phosphatidylcholine-phosphatidylserine vesicles, and activated bovine platelets. Reactions were monitored continuously through the enhanced fluorescence accompanying the interaction of newly formed thrombin with dansylarginine-N-(3-ethyl-1,5-pentanediyl) amide. The complete prothrombinase (Factor Xa, Ca2+, phospholipid, and Factor Va) behaved as a "typical" enzyme and catalyzed the activation of prothrombin with an apparent Vmax of 2100 mol of thrombin/min/mol of Factor Va or Factor Xa, whichever was the rate-limiting component. Regardless of whether the enzymatic complex was composed of Factor Xa, Ca2+, and plasma Factor Va plus phospholipid vesicles, or activated platelets in the place of the latter components, similar specific activity values were observed. The combination of Factor Va, Ca2+, and phospholipid enhanced the rate of the Factor Xa-catalyzed activation of prothrombin by a factor of 278,000. Factor Va itself when added to Factor Xa, Ca2+, and phospholipid, enhanced the rate of prothrombin activation by a factor of 13,000. Unactivated Factor V appears to possess 0.27% of the procoagulant activity of thrombin-activated Factor Va. From the kinetics of prothrombinase activity, an interaction between Factor Xa and both Factor V and Factor Va was observed, with apparent 1:1 stoichiometries and dissociation constants of 7.3 x 10(-10) M for Factor Va and 2.7 x 10(-9) M for Factor V. The present data, combined with data on the equilibrium binding of prothrombinase components to phospholipid, indicate that the model prothrombinase described in this paper consists of a phospholipid-bound, stoichiometric complex of Factor Va and Factor Xa, with bound Factor Va serving as the "binding site" for Factor Xa, in concert with its proposed role in platelets.
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PMID:The contribution of bovine Factor V and Factor Va to the activity of prothrombinase. 50 Jun 17

Fourteen patients with a documented sudden neurosensory hearing loss and four patients with other diseases causing neurosensory hearing loss were studied. The standardized coagulation workup included hematocrit, activated partial thromboplastin generation time, thrombin generation, prothrombin time, phase platelet count, platelet adhesivity, protamine sulfate, serum antithrombin III activity, fibrinogen, and Factor VIII values. Ony those patients having documented evidence of a neurosensory hearing loss occurring within hours or days were included in this study. Eight of the 14 paitents with a documented sudden neurosensory hearing loss satisfied our laboratory criteria for a diagnosis of in vitro hypercoagulability. Three of these patients had abnormal thrombin generation values, 4 had abnormal serum antithrombin III values, and 1 had an elevated platelet count. Four other patients with other diseases causing neurosensory hearing loss did not show evidence of in vitro hypercoagulability. It would appear from this data that coagulation abnormalities play a role in the pathogenesis of sudden neurosensory hearing loss.
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PMID:Hypercoagulability as a cause of sudden neurosensory hearing loss. 50

Thrombus weight was used as a measure of the thrombus enhancing effect of drugs in 135 rats. The weight of thrombus formed in one hour, on a 20 x 0.5 mm platinum wire, inserted in the vena cava was taken as a measure of thrombosis. The change in thrombus weight which followed the injection of ellagic acid to activate the coagulation system, adenosine diphosphate to activate the platelets, and epsilon-aminocaproic acid to inhibit the fibrinolytic system, was measured. Pilot studies showed that the drug doses used brought about the appropriate changes in the factors named. The mean thrombus weight in 45 control animals was 1.93 mg. Ellagic acid increased it about five-fold, and epsilon-aminocaproic acid almost two-fold, while adenosine diphosphate reduced it by almost a half. Concurrent controls were used in each case. Clotting tests (whole blood clotting time, kaolin-activated whole blood clotting time, thrombin time, and partial thromboplastin time), performed at the end of the hour, showed no significant correlation with thrombus weight.
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PMID:Thrombus weight as a measure of hypercoagulability induced by drugs. 50 92

Bovine platelets that have been activated by thrombin facilitate the conversion of prothrombin to thrombin in the presence of calcium ions and factor Xa. Activated protein C, a vitamin-K-dependent plasma protein, inhibits this platelet prothrombin-converting activity. The inhibition is time dependent and is not reversed by increasing concentrations of factor Xa. However, factor Xa is able to protect the platelet prothrombin-converting activity from inactivation by activated protein C. The activated protein C causes a parallel loss of factor Xa receptor sites and platelet prothrombin-converting activity. Activated protein C may contribute to the regulation of clotting through inactivation of the platelet prothrombin-converting activity.
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PMID:Activated protein C inhibits platelet prothrombin-converting activity. 50 37

The effect of collagen on isolated platelets, platelet-rich plasma and whole blood has been studied. Collagen failed to generate factor XIa-like activity in mixtures of isolated platelets, collagen and Ca++. Moreover, collagen added to whole blood or platelet-rich plasma containing 125I-factor IX and Ca++, also failed to form cleaved (activated) factor IX. In preliminary studies, lysed endothelial cells were found to enhance the formation of factor Xa and thrombin and to induce cleavage of 125I-factor IX in normal plasma, factor XII and factor-XI-deficient plasma even in the presence of antibody to tissue factor.
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PMID:The role of endothelial cells and subendothelial components in the initiation of blood coagulation. 51 Oct 12

1. Activated factor XIII is the enzyme that covalently cross-links fibrin monomers into fibrin polymers and results in increased clot strength and resistance of the clot to fibrinolysis. 2. Small amounts (greater than 1% of normal) of factor XIII are necessary for normal in vitro and in vivo activity. 3. Factor XIII deficiency is a rare autosomal recessive illness in which a hemorrhagic diathesis is caused by the virtual absence of the active a subunit of factor XIII. Approximately 100 cases have been described. 4. The disease in homozygotes is characterized by umbilical stump bleeding, a high incidence of fetal wastage, delayed soft tissue hemorrhage, and a high incidence of intracranial bleeding. The heterozygote is asymptomatic. 5. This paper calls attention to the apparent high incidence of oligospermia and small testes seen in homozygote males. Otherwise secondary sex characterics are normal. 6. Because there is no abnormality in thrombin generation and conversion of fibrinogen to fibrin, route coagulation tests (prothrombin time, partial thromboplastin time, thrombin time, etc.) are normal. Platelet function tests are normal. 7. Clots made from recalcified plasma severely deficient in factor XIII are soluble in 5 M urea or 1% monochloroacetic acid. These screening tests are simple and nearly pathognomonic of the illness. 8. More sophisticated and quantitative tests (e.g., dansylcadaverine incorporation) are available for definitive diagnosis and heterozygote detection. 9. Replacement treatment of the illness is simple, effective, and relatively inexpensive. Due to the long half-life of infused factor XIII and the small amounts necessary for normal hemostasis, prophylaxis is feasible and encouraged.
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PMID:Factor XIII. 51 66


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