Abolition by dextran sulfate of the heparin-accelerated antithrombin III/thrombin reaction

Dextran sulfate did not inhibit the amidolytic activity of thrombin on Boc-Val-Pro-Arg-4-methylcoumaryl-7-amide, but abolished inhibition of the enzyme with antithrombin III (AT III) in the presence of heparin. Dextran sulfate did not bind to AT III and had less affinity than immobilized heparin for the protein. Dextran sulfate bound strongly to thrombin and had higher affinity than immobilized heparin for the enzyme. These findings indicate that binding of dextran sulfate to a site other than the active site of thrombin to prevent the approach of AT III in the presence of heparin.