Heparin with thrombin

The kinetics of the lytic effect displayed by the complexes of immobilized heparin with thrombin and fibrinogen, in distinction from those with plasmin, are described by their saturation curves. The observed slowing down of the dissolution of unstabilized fibrin is probably due to the inhibiton of the lytic activity of the complexes by the soluble products of the reaction. In fact, as it was shown in Ref. 106, further addition of immobilized heparin-protein complex to partially hydrolyzed fibrin results in a complete recovery of the dissolution rate. 

Complexation of antithrombin with thrombin (and probably also with other proteinases) occurs by formation of a covalent bond which, by subsequent splitting, produces unaltered proteinase and irreversibly modified antithrombin.405,406 The strength of heparin-antithrombin complexes, as determined by u.v.-difference,405 fluorescence,406,407 af-... 

Heparin cofactor II, when activated by binding to glycosaminoglycans (dermatan sulfate, heparins, and heparin), inhibits thrombin (24). The 43-kDa serpin, proteinase nexin 1, possesses 30% sequence homology with ATIII and can be activated by binding to heparin to inhibit several serine proteinases including thrombin (25). Proteinase nexin 2 is found within the platelet a-granule and is released when platelets are activated (26). It is able to inhibit factor XIa. 

Another serine protease inhibitor of the al-antitrypsin family (serpin) is heparin cofactor II (HCII), which also forms a 1 1 complex with thrombin, but does not react with factor Xa [4,10]. The rate of inhibition of thrombin is not only increased by heparinoids but also by the related glycosaminoglycan dermatan sulfate. The identification of an inhibitor variant and site-directed mutagenesis studies on HC II cDNA led to the understanding that the binding sites for heparin and dermatan sulfate may be overlapping but not identical. Further proteinase inhibitors interacting with heparinoids are tissue factor pathway inhibitor and protease nexin-1. 

The anticoagulant activity of heparin is endowed by its ability to form strong complexes with a variety of blood clotting factors and thus neutralize their action. For instance, heparin interacts with thrombin, fibrinogen, prothrombin, factors IX-XII... 

It is noteworthy that a qualitatively similar dependence was observed for heparin in solution116>. The complexes of immobilized heparin with fibrinogen and thrombin are rather stable (the corresponding association constants for the complexes with fibrinogen and thrombin are (1.4 0.5) x 105 M and (8 2) x 10s A/-1) and are not subjected to dissociation in physiological solution. 

Fig. 8. Kinetics of unstabilized fibrin hydrolysis with complexes of immobilized heparin with fibrinogen (1), thrombin (2), fibrinolysin (plasmin) (3), and serum albumin (4),06)...

The more profound and extensive effect of immobilized heparin on the blood clotting system observed in the presence of immobilized trypsin is due to the tryptic lysis of the protein constituents of the complexes of immobilized heparin with the most thrombogenic plasma proteins (thrombin and fibrinogen) (Fig. 11). 

Miyata S. Editorial comment to Heparin-induced thrombocytopenia and treatment with thrombin inhibitors . Jpn J Thromb Hemost 2005 16 621-622. 

Interestingly, FpA also increased despite maximal anticoagulation with heparin. The correlation between increased FpA plasma levels and increased incidence of complications and ischemic events indicated the involvement of heparin-resistant thrombin activity into the failure of the intervention... 

Oltrona L, Eisenberg PR, Lasala JM, et al. Association of heparin resistant thrombin activity with acute ischemic complications of coronary interventions. Circulation 1996 94 2064-2071. 

Active clotting factors (lla, IXa, Xa, Xla, Xlla, Xllla) a-globulin that inhibits serine proteases, including several of the clotting factors, for example, thrombin (Factor II, Figure 20.5). In the absence of heparin, antithrombin III interacts with thrombin... 

Inactive factors [Note While the heparin-antithrombin III complex readily inactivates thrombin, the complex of low molecular weight heparin with... 

Snellman, Sylven and Julen isolated the heparin polypeptide and showed that this material is a potent antithrombin on thrombin with purified fibrinogen, suggesting that heparin in the mast cells is in the active anticoagulant form. Electrophoresis shows that this native heparin forms a complex compound with thrombin and also with a lipoprotein molecule. They conclude the whole heparin complex is produced in the intergranular cytoplasm of the tissue mast cells. 

These anticoagulant polymers may be divided into two major categories, namely "AT Ill-like" or "heparin-like" materials, according to their different interaction mechanisms with thrombin... 

In the present paper, we report high-performance affinity chromatography of thrombin in presence of AT III and Hep, using two types of resins as stationary phases either heparin-like PSSO or AT Ill-like PAOM. In order to differentiate their mechanisms of interaction with thrombin, we examined the chromatographic behavior of thrombin in the presence, or in the absence of AT III and/or heparin. Finally, thrombin was injected on the columns at low ionic strength. The desorption of bound thrombin from the two solid surfaces was then carried out using AT III, heparin and the AT Ill-Hep complex, to elucidate the specificity of the interactions involved. 

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