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)

One hundred patients were screened for hypercoagulability preoperatively and on the third, seventh, tenth, fourteenth, and twenty-first days postoperatively. Patients found to have hypercoagulability were treated with heparin, aspirin, and Coumadin. When the abnormality was present preoperatively, treatment was continued for the duration of the patient's life. Those patients in whom abnormalities developed postoperatively were given anticoagulants until cardiac catheterization 6 months following their operation. Twenty-four of the 100 patients had no coagulation abnormalities preoperatively or postoperatively. Fifteen patients were found to have abnormality prior to operation. Their predominant abnormality was low antithrombin III activity. Sixty-one patients became hypercoagulable postoperatively. Predominant abnormality in this group of patients was increased thrombin generation and increased platelet adhesiveness. Evaluation of patients in this study group revealed a decrease in the incidence of pulmonary embolism, an increase in the patency of vein grafts, and the elimination of anticoagulant therapy in 24 percent of the patients.
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PMID:Coagulation abnormalities in patients undergoing myocardial revascularization. 30 43

Local inflammation, induced by s.c. injection of turpentine, evoked characteristic changes in the metabolism of antithrombin III, and alpha1-antitrypsin. For a period of approximately 36 h, the plasma half-lives of both protease inhibitors were shortened to 70--74% of the respective preinjection values. Similar changes were also observed in the slope of iodine-labelled albumin, suggesting that increased capillary permeability was primarily responsible for the losses of labelled proteins from the circulation. Incorporation of [3H]- or [14C]-leucine into albumin changed little during inflammation, but markedly increased values were measured for anti-thrombin III (3-fold), alpha1-antitrypsin (4-fold) and, above all, for fibrinogen (7-fold) 24 h and 48 h after the injection of turpentine. These changes in synthesis and elimination rates resulted in the following net balances: fibrinogen concentrations in plasma rose substantially during the early phase of inflammation; alpha1-antitrypsin concentrations increased gradually but to a significantly lesser extent, peak concentrations being reached after a reverse trend in fibrinogen concentrations had become apparent; antithrombin III concentrations remained steady throughout at levels which were only marginally above the pretreatment values.
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PMID:Effect of experimental inflammation on the synthesis and distribution of antithrombin III and alpha1-antitrypsin in rabbits. 30 65

Antithrombin III is one of the main inhibitors in the blood coagulation mechanisms. Thrombin and factor Xa are slowly inactivated by it, as well as other serine proteinases of the coagulation mechanisms. Heparin tremendously accelerates the inhibitory function of antithrombin III. In the process antithrombin III activity is also reduced. Heparin retards the thrombin-fibrinogen reaction, but otherwise the effectiveness of heparin as an anticoagulant depends on antithrombin III in laboratory experiments, as well as in therapeutics. The activation of prothrombin is inhibited, and any thrombin or other vulnerable protease that might generate becomes inactivated. The measurement of antithrombin III concentration in blood is now achieved by research methods, as well as by methods that are practical for routine use. The tests require either thrombin or factor Xa as substrate, and could be specific for antithrombin III. There are congenital as well as acquired deficiencies of antithrombin III. The inhibitor is also found in tissues.
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PMID:Antithrombin III. Theory and clinical applications. H. P. Smith Memorial Lecture. 34 19

After introductory notes on the history of heparin research the chemistry of this mucopolysaccharide is described. It is shown that the chemistry of heparin cannot be exactly described by one chemical formula because heparin represents a family of compounds with different chain-length. Molecular features responsible for the high structural specificity of anticoagulant activity are described. The present status of knowledge on the mechanism of the anticoagulant action of heparin is described in detail. It is shown that basic mechanism is the acceleration of the interaction of antithrombin III with the clotting factors IXa, Xa, XIa, XIIa, and thrombin which are known to be serine proteases. The effects of heparin of platelet function, lipid composition of blood, and on fibrinolysis reflect its complex influence on hemostasis. After a description of side effects and toxicity clinically relevant data on its pharmacocinetics are given.
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PMID:[Pharmacology of heparin]. 37 77

Anticoagulants in the form of heparin, dipyridimole, steroids, prostaglandin E1, Macrodex, and antithrombin III were administered in separate experiments prior to endotoxin infusion in the dog. The pattern of disseminated intravascular coagulation (DIC) developed consistently when endotoxin alone was administered. Heparin dosages from 1 to 10 mg/kg did not influence the appearance of thrombocytopenia but effectively eliminated the decrease in fibrinogen levels ordinarily found. Antithrombin III (AT III), obtained from the National Red Cross, administered in a dose designed to provide a doubling of the circulating AT III, reduced the fibrinogen utilization to a similar degree as heparin without affecting the platelet loss. Dipyridimole, as administered, was ineffective in this model, and did not alter the development of thrombocytopenia or the hypofibrinogenemia. Steroids, Macrodex, and prostaglandin E1 had minimal effect on the coagulopathy. Our finding would suggest that the endotoxin effect on dog platelets id direct, and not mediated by thrombin, and that the role of heparin in the clinical management of DIC should be considered only in instances in which renal complications exist.
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PMID:Endotoxin-induced intravascular coagulation (DIC) and its therapy. 40 May 81

The conformational aspects of the binding of antithrombin III to thrombin were investigated by difference spectroscopy, circular dichroism, and optical rotatory dispersion. The CD and ORD studies indicate an increase of 6--8% in alpha-helix content at the expense of the beta structure, while the results from difference spectroscopy showed an increased exposure of approximately seven tyrosine residues. In the presence of heparin there is a slightly greater increase in helicity which is accompanied by exposure of an average of two tryptophan and one tyrosine residues. These spectral results indicate that the thrombin-antithrombin III complex formed in the presence of heparin differs in its conformation from that produced in its absence.
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PMID:Conformational changes accompanying the binding of antithrombin III to thrombin. 42 Aug 17

Rabbit antithrombin III and thrombin were purified to homogeneity to determine the in vivo relationship of these proteins in an autologous system. These proteins, radiolabeled with Na[125I], were injected into rabbits to determine the circulatory half-life. The mean half-life values were 125I-antithrombin III, 54.75 +/- 3.10 hr; 125I-thrombin, 7.25 +/- 1.49 hr; 125I-thrombin-antithrombin III, 7.25 +/- 1.09 hr; 125I[thrombin-antithrombin III], 11.13 +/- 0.88 hr; and Tos-Lys-CH2Cl-125I-thrombin, 27.75 +/- 3.18 hr. All the mean half-life values were statistically different from that of thrombin alone except for the two forms of thrombin-antithrombin III complex. Following injection of the radiolabeled proteins, plasma samples were obtained and gel-filtered to analyze the molecular weight distribution of the radiolabel. An identical elution position on gel filtration of 125I-antithrombin III with native antithrombin III was observed. The 125I-thrombin distributed into two peaks of radioactivity, with a molecular weight of 100,000 (79%) and a molecular weight greater than 200,000 (21%). The 100,000 dalton peak is consistent with a thrombin--antithrombin III complex, and the greater than 200,000 dalton peak is consistent with a thrombin-alpha 2-macroglobulin complex as confirmed by in vitro immunochemical studies. Thrombin inactivated with Tos-Lys-CH2Cl also showed two peaks of radioactivity on gel filtration, one peak which was excluded from the column and the other peak with an elution volume that was consistent with the position of native thrombin.
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PMID:Correlation of in vivo and in vitro inhibition of thrombin by plasma inhibitors. 42 64

The rate of the reaction between thrombin and antithrombin III is greatly increased in the presence of heparin. Several mechanisms for this effect are possible. To study the problems commercial heparin was fractionated into one fraction of high anticogulant activity and one of low anticoagulant activity by affinity chromatography on matrix-bound antithrombin III. The strength of the binding of the two heparin fractions to antithrombin III and thrombin, respectively, was determined by a crossed immunoelectrophoresis technique. As was to be expected, the high activity fraction was strongly bound to antithrombin III while the low activity fraction was weakly bound. In contrast, thrombin showed equal binding affinity for both heparin fractions. The ability of the two heparin fractions to catalyse the inhibition of thrombin by antithrombin III was determined and was found to be much greater for the high activity heparin fraction. A mechanism for the reaction between thrombin and antithrombin III in the presence of small amounts of heparin is suggested, whereby antithrombin III first binds heparin and this complex then inhibits thrombin by interaction with both the bound heparin and the antithrombin III.
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PMID:Studies on the mechanism of the rate-enhancing effect of heparin on the thrombin-antithrombin III reaction. 43 23

The effect of prothrombin fragment 2 on the inhibition of thrombin by antithrombin III has been studied. Fragment 2 was found to slow the rate of inhibition of thrombin by antithrombin III about 3-fold. The effect of prothrombin fragment 2 on antithrombin III inhibition was examined by comparing its action in the presence of either thrombin or meizothrombin (des fragment 1). The second order rate constants for antithrombin III inhibition of thrombin with saturating fragment 2 and antithrombin III inhibition of meizothrombin (des fragment 1) were the same. Prothrombin fragment 2 had no effect on either antithrombin III inhibition of meizothrombin (des fragment 1) or Factor Xa. The effect of the fragment on the reaction mechanism of thrombin inhibition was evaluated to see if the fragment altered binding of antithrombin III to thrombin or inhibited the formation of the covalent complex. The fragment was found to have no inhibitory effect on the rate of covalent complex formation, indicating that the protective effect of the fragment is by inhibiting binding of antithrombin III to thrombin. These data suggest that prothrombin fragment 2 may be an important factor in controlling the localization of clot formation by regulating the interaction between thrombin and antithrombin III.
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PMID:The effect of prothrombin fragment 2 on the inhibition of thrombin by antithrombin III. 44 71

Four different heparin assay methods were compared. Only procedures which can be routinely carried out in clinical laboratories were taken into consideration. A range of heparin concentrations was chosen for these tests which is likely to be expected in low dose heparin prophylaxis. The lowest sensitivity was found when the thrombin clotting time was applied, and slightly better results were obtained by the aPTT method. Addition of purified antithrombin III to the reaction mixtures improved the sensitivity of both methods. When factor Xa was used in a clotting test, the results were comparable to the aPTT method. The sensitivity was however, about 10 times higher when the remaining factor Xa was directly measured in a photometric assay system with a chromogenic substrate. The advantages and disadvantages of the different methods and the usefulness of heparin assays for clinical purposes are discussed.
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PMID:[Heparin assay in plasma. Comparison of different methods (author's transl)]. 46 52


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