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)

Disseminated intravascular coagulation (DIC) was produced by an infusion of a prothrombin activator (Echis carinatus venom; 30 minutes; 0.5 NIH thrombin equivalent U/kg) in mongrel dogs (Echis group, n = 7). Fibrinogen declined to below measurable levels (less than 25 mg/dl), and fibrin-fibrinogen degradation products appeared (53 +/- 8 micrograms/ml) at end venom infusion in the Echis group. These alterations were not seen when an irreversible thrombin inhibitor, D-phenylalanyl-L-prolyl-L-arginine-L-chloromethyl ketone (PPACK) (57 nmol/kg/min for 120 minutes), was given alone (PPACK group, n = 5) or in association with venom (Echis + PPACK group, n = 5). Factor II activity (1% +/- 1%) in the Echis and Echis + PPACK groups was significantly below the PPACK (55% +/- 9%) and the control (79% +/- 2%) levels at 120 minutes. In contrast, factor VIII coagulant (factor VIII:C) activity in the Echis group (1% +/- 1%) remained significantly below that in the Echis + PPACK (68% +/- 8%), PPACK (78% +/- 10%), and control (91% +/- 9%) groups at this interval. No change in factors X (91% +/- 7% to 81% +/- 7%, P not significant) and VII (64% +/- 10% to 48% +/- 11%, P not significant) activities were observed. Hemolysis was observed only in the Echis group, whereas thrombocytopenia and leukopenia were noted in both the Echis and the Echis + PPACK groups. These data show that large amounts of E. carinatus venom produce rapid DIC in vivo, because of the activation of prothrombin. In contrast, the decline in factor VIII:C activity appeared to be the result of the liberated thrombin. PPACK antagonized all of the venom-released thrombin without any major deleterious clotting abnormalities. This inhibitor appears to prevent thrombin-mediated DIC in vivo. In contrast, heparin was found to be an unreliable antagonist of the venom-released thrombin in vitro. PPACK also inhibited the marked hemolysis usually observed after venom. In addition, we found that the esterolytic (N-benzoyl-L-prolyl-L-phenylalanyl-L-arginine-p-nitroanilide HCL) activity of E. carinatus venom degrades fibrinogen in vitro.
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PMID:Disseminated intravascular coagulation following Echis carinatus venom in dogs: effects of a synthetic thrombin inhibitor. 308 70

Kinetic parameters [the Michaelis-Menten (Km), catalytic (kcat), and specificity (kcat/Km) constants] were determined for human alpha- and gamma-thrombins with the chromogenic substrate S-2238 (H-D-Phe-Pip-Arg-p-nitroanilide), Chromozym-TH (Tos-Gly-Pro-Arg-p-nitroanilide), and Spectrozyme-TH (H-D-HHT-Ala-Arg-p-nitroanilide) under physiologically relevant conditions (0.15 M NaCl buffered with 10 mM HEPES and 10 mM Tris-HCL, pH 7.4 at 37 degrees C). No major differences were found between alpha-thrombin with high fibrinogen clotting activities (greater than 3,500 killo clotting units/g) and gamma-thrombin with essentially no clotting activities (less than 10 kCU/g), although the Km values and in most cases kcat values for alpha-thrombin were slightly lower than for the gamma-thrombin. At 37 degrees C, relative to 23 degrees C, Km values increased 2-fold for S-2238, approximately 1.5-fold for Chromozym-TH, and remained essentially the same for Spectrozyme-TH (e.g., reciprocal substrate binding), whereas the kcat values increased for all 3 substrates (e.g., enzyme turnover). This caused kcat/Km values to decrease slightly for S-2238, remain the same for Chromozym-TH, and increase for Spectrozyme-TH (e.g., enzyme efficiency). Since spontaneous hydrolysis was not limiting at 37 degrees C, assays employing these substrates may be satisfactorily performed under physiologically relevant conditions. Under these conditions, kcat/Km ratios for the 3 substrates are similar to that for the A alpha cleavage in fibrinogen by alpha-thrombin.
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PMID:Human alpha- and gamma-thrombin specificity with tripeptide p-nitroanalide substrates under physiologically relevant conditions. 361 13

The antiplatelet effect of the pyridazinone analogue, 4, 5-dihydro-6-[4-[2-hydroxy-3-(3,4 dimethoxybenzylamino)propoxy]naphth-1-yl]-3(2H)-pyridazinone (HCL-31D), was investigated in vitro with rabbit platelets. HCL-31D dose-dependently inhibited the platelet aggregation and ATP release induced by collagen (10 microg/ml), arachidonic acid (100 microM) or thrombin (0.1 U/ml) with an IC(50) of about 0.95-5.41 microM. HCL-31D (0.5-5 microM) increased the platelet cyclic AMP level in a dose-dependent manner. Furthermore, HCL-31D potentiated cyclic AMP formation caused by prostaglandin E(1) but not that caused by 3-isobutyl-1-methylxanthine (IBMX). HCL-31D also attenuated phosphoinositide breakdown and intracellular Ca(2+) elevation induced by collagen, arachidonic acid or thrombin. HCL-31D inhibited the formation of thromboxane B(2) induced by collagen or thrombin but not by arachidonic acid. In addition, HCL-31D did not affect platelet cylooxygenase and thromboxane synthase activity. These data indicate that HCL-31D is an inhibitor of phosphodiesterase and that its antiplatelet effect is mainly mediated by elevation of cyclic AMP levels.
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PMID:Mechanism of inhibition of platelet aggregation by HCL-31D. 1065 Jan 52