Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.2.2.7 (heparinase)
 1,270 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rabbit thrombomodulin (TM) influences blood coagulation by serving as a cofactor for thrombin-induced protein C activation (activity a), by directly affecting the procoagulant activity of thrombin (activity b) and by accelerating the inhibition of thrombin by antithrombin III (AT III) (activity c). Although high molecular weight cationic compounds, such as poly-L-lysine and the ionophore-releasate from human platelets, only partly affected activity a in a concentration-dependent manner, activities b and c, however, were almost totally inhibited by these cationic compounds. Likewise, a heparin- and dermatan sulfate-binding peptide which represents a portion of the glycosaminoglycan-binding domain of vitronectin (VN) selectively inhibited activities b and c, indicating the presence of clustered acidic domain(s) in TM responsible for these activities. While heparinase or heparitinase did not affect rabbit TM function at all, digestion of rabbit TM with chondroitin ABC-lyase abolished activities b and c, whereas activity a remained unaffected. Modification of rabbit TM with chondroitin ABC-lyase was associated with a decrease in molecular mass of the receptor by about 10 kDa and a 2- to 3-fold decrease in affinity to thrombin as deduced from direct binding studies. These results suggest that at least two acidic thrombin binding domains are present in rabbit TM, whereby a dermatan sulfate-like glycosaminoglycan moiety constitutes the secondary binding domain for thrombin, eliciting both the direct as well as the AT III-dependent anticoagulant function of rabbit TM (activities b and c) but not protein C activation (activity a). In contrast to rabbit TM, human TM isolated from placenta only showed weak activities b and c. These differences in reactivity of TM from different sources appeared to be due to the masking (or absence) of the proposed secondary thrombin binding site in human TM, since VN could be identified as a major contamination in the human TM preparation as revealed by enzyme-linked immunosorbent assay and Western blot analysis. In addition, the major part of human TM could be immunoprecipitated by monospecific antibodies to VN. These findings indicate a possible modulatory function for VN in the human thrombin-TM system.
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PMID:Domain structure of the endothelial cell receptor thrombomodulin as deduced from modulation of its anticoagulant functions. Evidence for a glycosaminoglycan-dependent secondary binding site for thrombin. 215 59

It had been suggested that antithrombin activity on the surface of intact endothelial cells may play a role in inhibiting platelet adhesion and thrombus formation. The antithrombin activity may be due to thrombomodulin or to activation of antithrombin III by glycosaminoglycans or thrombomodulin, or possibly a combination of these. This inhibitory activity has been shown to be affected by such antiheparin agents as protamine, hexadimethrine bromide (Polybrene; Aldrich Chemical Co., Milwaukee, Wis.) and platelet factor 4, as well as by such enzymes as heparinase and heparitinase. We have used a hamster cheek pouch preparation to observe thrombus formation in vivo in a normal vascular flow, to determine whether the production of thrombi by thrombin can be enhanced by antiheparin agents. After intra-arterial injection or topical application of protamine or hexadimethrine bromide, platelet adhesion and thrombus formation on intact arteriolar endothelium was produced by a dose of thrombin, which when injected alone had no effect. No thrombi were found in venules or capillaries. Injection of heparin before or after the antiheparin agents necessitated a larger dose to enhance the action of thrombin. On electron microscopy the thrombi were found to consist primarily of platelets adherent to an intact endothelium. The possible clinical implications of these observations are discussed.
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PMID:Production of thrombi on intact endothelium by use of antiheparin agents in vivo. 224 59

Thrombomodulin isolated from rabbit lung was separated by ion-exchange chromatography on DEAE-cellulose into a retarded (acidic) and a nonretarded (nonacidic) fraction. Both fractions contained the cofactor required for the activation of protein C. In addition, the acidic fraction (but not the nonacidic fraction) prevented the clotting of fibrinogen by thrombin ("direct" anticoagulant activity) and accelerated the inhibition of thrombin by antithrombin (effect corresponding to 2-10 international units of heparin per mg of protein). Both of these activities were readily neutralized by the synthetic polycation Polybrene, which did not appreciably affect protein C activation. They were also eliminated by digestion of thrombomodulin with bacterial heparinase, which, in addition, converted the acidic form of the protein C activation cofactor to a nonacidic form. Similar conversion observed during storage of thrombomodulin was attributed to endogenous proteinase activity. Density-gradient centrifugation of the acidic form of thrombomodulin in CsCl/4M guanidinium chloride failed to separate either of the direct or antithrombin-dependent anticoagulant activities from the protein C activation cofactor, which showed a buoyant density of 1.31-1.34 g/ml. The nonacidic cofactor had a lower density, 1.26-1.28 g/ml. Unreduced thrombomodulin yielded two major fractions of protein C activation cofactor on NaDodSO4/PAGE, with apparent Mr of approximately 68,000 and 57,000, respectively. The larger component contained essentially all of the direct and antithrombin-dependent anticoagulant activities. We propose that these activities as well as the negative charge and the higher buoyant density of the acidic, Mr 68,000 form of thrombomodulin are due to a heparin-like polysaccharide and, further, that this component can be separated from the major portion of the molecule, which contains the protein C activation site, through the action of a proteinase.
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PMID:Functional domains of rabbit thrombomodulin. 301 29