Inactivation of α- and β-Thrombin by Antithrombin-III and Heparin

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Abstract
Inactivation of α- and β-thrombin by antithrombin-III and heparin was studied, since it had been suggested that two forms of thrombin exist with respect to heparin sensitivity (Machovich 1975b). It was found that the inactivation rates of α- and β-thrombin by antithrombin were different, namely α-thrombin was more sensitive to antithrombin than β-thrombin. Heparin facilitated the complex formation between α-thrombin and antithrombin-III, whereas β-thrombin inactivation was only slightly affected. Furthermore, heparin protected α-thrombin against the inactivating effect of heat, while β-thrombin lost its activity during the heat treatment. These findings suggest that the formation of β-thrombin in blood circulation may have an important role in thrombosis predisposition.