Comparison of the kinetic behavior of human and bovine proteins in the heparin-catalyzed antithrombin III/thrombin reaction

Abstract

Significant differences between saturation kinetic properties of heparin-stimulated reactions between thrombin and antithrombin III from human and bovine species were observed. In both systems, the apparent K m for antithrombin III was higher than the K D for antithrombin III-heparin interaction, monitored by intrinsic protein fluorescence change. The K m for thrombin and k cat were much higher for proteins of the human species than the bovine species. The apparent K m for one human protein was dependent on the concentration of the other human protein, indicating interaction of the binding events. The reaction product formed from the bovine proteins was a potent inhibitor of the reaction but the product from the human proteins was a poor inhibitor. The major differences between the two species appeared to be related to interaction of thrombin or thrombin derivatives with heparin or heparin-antithrombin III complexes.