Question

7. Heparan sulfate and heparin are related glycosaminoglycans that differ primarily in the number of sulfate groups (heparin is more highly sulfated). Heparin has one of the highest negative charge densities ever found in a biomolecule and is used commercially to prevent blood clotting. The molecular structure of heparin is shown here. HỌCOO SO HO COO- OSO, OSO, OSO3 NH SO

Answer 1

Anticoagulative activity of commercial Heparin

unfractionated heparin (UFH)or simply Heparin, is used in medication and naturally occurring glycosaminoglycan. In other words it is a sulfated polysaccharide with a molecular weight range of 3000 to 30 000 Da (mean, 15 000 Da). Two types of heparins are widely used, unfractionated heparin (UFH) and low molecular weight heparin (LMWH). Low molecular weight heparin (LMWHs) are derived from heparin by enzymatic or chemical depolymerization to yield fragments approximately one third the size of heparin. LMWHs have a mean molecular weight of 4500 to 5000 Da with a distribution of 1000 to 10 000 Da.

They are generally used as an anticoagulant which will prevent the formation of clots and addition of existing clots within the blood. In general, it produces its major anticoagulant effect by inactivating thrombin and (factor Xa) through an antithrombin (AT)-dependent mechanism. The anticoagulant activity of heparin arises primarily from its ability to bind to antithrombin III (AT III, which is an anti-coagulation factor) altering the conformation and accelerating the rate at which antithrombin inhibits clotting enzymes, particularly thrombin and activated factor X (factor Xa)by covalent binding, finally resulting in reduced coagulation.

However, there are differences between UFH and LMWH in their anticoagulant activities.The anticoagulant and other biological differences between unfractionated heparin (UFH) and LMWH can be explained by the relatively lower binding properties of LMWH. In comparison with UFH, LMWHs have reduced ability to inactivate thrombin because the smaller fragments cannot bind simultaneously to AT and thrombin. In contrast, because of bridging between AT and factor Xa is less critical for anti-factor Xa activity, the smaller fragments inactivate factor Xa almost like the larger molecules do. Since, most of the heparin molecules contain at least 18 saccharide units, UFH has an anti-factor Xa to anti-factor IIa ratio of 1:1. In contrast to UFH, commercial LMWHs have anti-factor Xa to anti-factor IIa ratios between 2:1 and 4:1, depending on their molecular size distribution.

Effect of Protamine sulfate

Protamine sulphate is a fish sperm derived basic protein mainly composed of poly(l-arginine). It is a polycationic, highly positively charged protein that can binds to heparin and form a stable salt. One milligram of protamine sulphate can neutralizes approximately 100 units of heparin. The mechanism of action of protamine sulfate involves binding to the negatively charged heparin molecules, forming a stable complex, and displacing antithrombin III (ATIII )from the heparin-ATIII complex.