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)

Heparan sulphate/heparin subfractions with high plasma anti-Xa activity have an unusual uronate composition, i.e. high proportions of both glucuronate and sulphated iduronate. These preparations inhibit the amidase activity of factor Xa in an uncompetitive mode and the prothrombin-activation catalyzed by Xa, both in the absence of antithrombin III. Subfractions of low affinity for antithrombin III are equally potent against Xa. The anti-X activity is destroyed by a 3-h periodate oxidation.
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PMID:Demonstration of a direct anti-factor Xa activity in certain heparin-related glycosaminoglycans. 711 18

Chondroitin sulfate from bovine tracheal cartilage, with the basic structure (4-O-sulfo-D-GalpNAc beta-1-->4-D-GlcpA)n, was chemically modified by O-sulfonation. Depending on the reaction conditions, the products showed a different degree of O-sulfonation. A fully O-sulfonated chondroitin sulfate, having no free hydroxyl groups, and a sulfo ester group:disaccharide unit ratio of 4.0 was prepared. This chondroitin sulfate derivative was shown by 1H NMR spectroscopy to have a uronate residue with an altered conformation. Usually, the uronate residue in chondroitin sulfate resides in the 4C1 form. Fully O-sulfonated chondroitin sulfate had an uronate residue in the 1C4 form at 30 degrees C, similar to the preferred conformation of the 2-O-sulfo-iduronate residue most commonly found in heparin. The 2S0 form of the uronate residue was also found in fully O-sulfonated chondroitin sulfate at 60 degrees C. The anti-factor IIa activity of fully O-sulfonated chondroitin sulfate was 40 units/mg. This value is similar to the activities reported for various low-molecular-weight heparins, and substantially higher than those previously reported for partially O-sulfonated chondroitin sulfates having an average sulfate group/disaccharide unit of 2.5 to 3.3. The anti-factor Xa activity of the fully O-sulfonated chondroitin sulfate was 12 units/mg. This value is considerably lower than the activities reported for various low-molecular-weight heparins, consistent with the critical importance of an antithrombin III pentasaccharide binding site for anti-factor Xa activity. These findings suggest that the conformational change of glucuronic acid residue in chondroitin sulfate resulting from its full O-sulfonation can result in enhanced anticoagulant activity, particularly as measured by anti-factor IIa assay.
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PMID:Conformational changes and anticoagulant activity of chondroitin sulfate following its O-sulfonation. 969 38

The anticoagulant activation of the serpin antithrombin by heparin pentasaccharide DEFGH was previously shown to involve trisaccharide DEF first binding and inducing activation of the serpin, followed by disaccharide GH binding and stabilizing the activated state [Petitou et al. (1997) Glycobiology 7, 323-327; Desai et al. (1998) J. Biol. Chem. 273, 7478-7487]. In the present study, the role of conformational changes and charged residues of the GH disaccharide in the allosteric activation mechanism was investigated with variant pentasaccharides modified in the GH disaccharide. Perturbation of the conformational equilibrium of iduronate residue G through replacement of the nonessential 3-OH of this residue with -H resulted in parallel decreases in the fraction of residue G in the skew boat conformer (from 64 to 24%) and in the association constant for pentasaccharide binding to antithrombin [(2.6 +/- 0.3)-fold], consistent with selective binding of the skew boat conformer to the serpin. Introduction of an additional sulfate group to the 3-OH of residue H flanking a putative charge cluster in the GH disaccharide greatly enhanced the affinity for the serpin by approximately 35-fold with only a small increase in the fraction of residue G in the skew boat conformation (from 64 to 85%). The salt dependence of binding, together with a recent X-ray structure of the antithrombin-pentasaccharide complex, suggested that the majority of the enhanced affinity of the latter pentasaccharide was due to direct electrostatic and hydrogen-bonding interactions of the H residue 3-O-sulfate with antithrombin. All variant pentasaccharides produced a normal enhancement of antithrombin fluoresence and normal acceleration of factor Xa inhibition by the serpin at saturating levels, indicating that conformational activation of antithrombin was not affected by the pentasaccharide modifications. Rapid kinetic studies were consistent with the altered affinities of the variant pentasaccharides resulting mostly from perturbed interactions of the reducing-end GH disaccharide with the activated antithrombin conformation and minimally to an altered binding of the nonreducing-end DEF trisaccharide to the native serpin conformation. Together, these results support a model in which the conformational flexibility of the G residue facilitates conversion to the skew boat conformer and thereby allows charged groups of the GH disaccharide to bind and stabilize the activated antithrombin conformation that is induced by the DEF trisaccharide.
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PMID:Mechanism of heparin activation of antithrombin: evidence for an induced-fit model of allosteric activation involving two interaction subsites. 973 84

In the framework of a project aimed at generating heparin-like sulfation patterns and biological activities in biotechnological glycosaminoglycans, different approaches have been considered for simulating the alpha(1-->4)-linked 2-O-sulfated L-iduronic acid (IdoA2SO(3))-->N,6-O-sulfated D-glucosamine (GlcNSO(3)6SO(3)) disaccharide sequences prevalent in mammalian heparins. Since the direct approach of sulfating totally O-desulfated heparins, taken as model compounds for C-5-epimerized sulfaminoheparosan (N-deacetylated, N-sulfated Escherichia coli K5 polysaccharide), preferentially afforded heparins O-sulfated at C-3 instead than at C-2 of the iduronate residues, leading to products with low anticoagulant activities, the problem of re-generating a substantial proportion of the original IdoA2SO(3) residues was circumvented by performing controlled solvolytic desulfation (with 9:1 v/v DMSO-MeOH) of extensively sulfated heparins. The order of desulfation of major residues of heparin GlcN and IdoA and of the minor one D-glucuronic acid was: GlcNSO(3)>GlcN6SO(3)>IdoA3SO(3) congruent with GlcA2SO(3) congruent with GlcN3SO(3)>IdoA2SO(3) congruent with GlcA3SO(3). Starting from a 'supersulfated' low-molecular weight heparin, we obtained products with up to 40% of iduronate residues O-sulfated exclusively at C-2 and up to 40% of their glucosamine residues O-sulfated at both C-6 and C-3. Upon re-N-sulfation, these products displayed an in vitro antithrombotic activity (expressed as anti-factor Xa units) comparable with those of current low-molecular weight heparins.
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PMID:Generation of anti-factor Xa active, 3-O-sulfated glucosamine-rich sequences by controlled desulfation of oversulfated heparins. 1172 96