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Prothrombinase Complex (prothrombinase + complex)
Selected AbstractsFactor V deficiency: a concise reviewHAEMOPHILIA, Issue 6 2008J. N. HUANG Summary., Factor V (FV; proaccelerin or labile factor) is the plasma cofactor for the prothrombinase complex that activates prothrombin to thrombin. FV deficiency can be caused by mutations in the FV gene or in genes encoding components of a putative cargo receptor that transports FV (and factor VIII) from the endoplasmic reticulum to the Golgi. Because FV is present in platelet ,-granules as well as in plasma, low FV levels are also seen in disorders of platelet granules. Additionally, acquired FV deficiencies can occur in the setting of rheumatologic disorders, malignancies, and antibiotic use and, most frequently, with the use of topical bovine thrombin. FV levels have limited correlation with the risk of bleeding, but overall, FV-deficient patients appear to have a less severe phenotype than patients with haemophilia A or B. The most commonly reported symptoms are bleeding from mucosal surfaces and postoperative haemorrhage. However, haemarthroses and intramuscular and intracranial haemorrhages can also occur. Because no FV-specific concentrate is available, fresh frozen plasma remains the mainstay of treatment. Antifibrinolytics can also provide benefit, especially for mucosal bleeding. In refractory cases, or for patients with inhibitors, prothrombin complex concentrates, recombinant activated FVIIa, and platelet transfusions have been successfully used. Some patients with inhibitors may also require immunosuppression. [source] Inherited defects of coagulation factor V: the hemorrhagic sideJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 1 2006R. ASSELTA Summary., Coagulation factor V (FV) is the protein cofactor required in vivo for the rapid generation of thrombin catalyzed by the prothrombinase complex. It also represents a central regulator in the early phases of blood clot formation, as it contributes to the anticoagulant pathway by participating in the downregulation of factor VIII activity. Conversion of precursor FV to either a procoagulant or anticoagulant cofactor depends on the local concentration of procoagulant and anticoagulant enzymes, so that FV may be regarded as a daring tight-rope walker gently balancing opposite forces. Given this dual role, genetic defects in the FV gene may result in opposite phenotypes (hemorrhagic or thrombotic). Besides a concise description on the structural, procoagulant and anticoagulant properties of FV, this review will focus on bleeding disorders associated with altered levels of this molecule. Particular attention will be paid to the mutational spectrum of type I FV deficiency, which is characterized by a remarkable genetic heterogeneity and by an uneven distribution of mutations throughout the FV gene. [source] Factor Xa is highly protected from antithrombin,fondaparinux and antithrombin,enoxaparin when incorporated into the prothrombinase complexJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 6 2003N. Brufatto Summary., Antithrombin and its cofactor, heparin, target both the product of prothrombin activation by prothrombinase, thrombin, as well as the enzyme responsible for the reaction, factor (F)Xa. These studies were carried out to quantify the effects of each of the prothrombinase components on the half-life of FXa in the presence of antithrombin and the low-molecular-weight heparins (enoxaparin, Aventis, Laval, Quebec, Canada) or the heparin pentasaccharide (fondaparinux, Organon Sanofi-Synthelabo, Cypress, TX, USA). Experiments were carried out using a recombinant form of prothrombin in which the active site serine has been mutated to cysteine and subsequently labeled with fluorescein. This mutant allowed calculation of the second order rate constant for inhibition of FXa by antithrombin in such a way that competition for antithrombin by thrombin is eliminated and competition for FXa by prothrombin is accounted for. Intrinsic rate constants for the inhibition of FXa by antithrombin,enoxaparin and antithrombin,fondaparinux, in the presence of the various prothrombinase components, were calculated. Addition of phospholipid had no significant effect on the second order rate constant for inhibition of FXa by antithrombin, while addition of FVa appeared to be mildly protective. Further addition of prothrombin however, caused profound protection of FXa, increasing its half-life from 1.1 to 353 s in the case of fondaparinux, and from 0.4 to 42 s in the case of enoxaparin. Similar results were reported for unfractionated heparin previously [1]. Therefore, in the presence of unfractionated heparin, fondaparinux, or enoxaparin, prothrombinase is profoundly protected from antithrombin. [source] Highly Potent and Selective Substrate Analogue Factor Xa Inhibitors Containing D -Homophenylalanine Analogues as P3 Residue: Part 2CHEMMEDCHEM, Issue 7 2007Anne Stürzebecher Dr. Abstract A series of highly potent substrate-analogue factor Xa inhibitors containing D -homophenylalanine analogues as the P3 residue has been identified by systematic optimization of a previously described inhibitor structure. An initial lead, benzylsulfonyl- d- hPhe-Gly-4-amidinobenzylamide (3), inhibits fXa with an inhibition constant of 6.0,nM. Most modifications of the P2 amino acid and P4 benzylsulfonyl group did not improve the affinity and selectivity of the compounds as fXa inhibitors. In contrast, further variation at the P3 position led to inhibitors with significantly enhanced potency and selectivity. Inhibitor 27, benzylsulfonyl- D -homo-2-pyridylalanyl(N-oxide)-Gly-4-amidinobenzylamide, inhibits fXa with a Ki value of 0.32,nM. The inhibitor has strong anticoagulant activity in plasma and doubles the activated partial thromboplastin time and prothrombin time at concentrations of 280,nM and 170,nM, respectively. Compound 27 inhibits the prothrombinase complex with an IC50 value of 5,nM and is approximately 50 times more potent than the reference inhibitor DX-9065a in this assay. [source] | ||||||||||