Decreased binding of heparin to antithrombin following the interaction between antithrombin and thrombin

A complex formed between bovine antithrombin and bovine thrombin was shown to elute from a heparin-agarose column at a lower ionic strength than free antithrombin. Moreover, it was demonstrated that less heparin remained attached to the antithrombin-thrombin complex than to free antithrombin, when mixtures of high-affinity heparin and either complex or antithrombin were separated by gel electrophoresis or gel chromatography under identical conditions. These results suggest that the interaction between antithrombin and thrombin leads to a decreased affinity of heparin for the antithrombin moiety of the complex. This decrease may be an essential feature of the proposed function of heparin as a catalyst in the antithrombin-thrombin reaction.