The inhibition of thrombin-dependent positive-feedback reactions is critical to the expression of the anticoagulant effect of heparin

Heparin catalyses the inhibition of two key enzymes of blood coagulation, namely Factor Xa and thrombin, by enhancing the antiproteinase activities of plasma antithrombin III and heparin cofactor II. In addition, heparin can directly inhibit the activation of Factor X and prothrombin. The contributions of each of these effects to the anticoagulant activity of heparin have not been delineated. We therefore performed experiments to assess how …