Heparin-sensitive and nonsensitive forms of thrombin.

Area of Science:

• Biochemistry
• Enzymology
• Protein Chemistry

Background:

• Thrombin is a key enzyme in hemostasis.
• Understanding thrombin's interactions with heparin is crucial for anticoagulant therapies.
• Differential properties of thrombin forms may impact its physiological and pharmacological roles.

Purpose of the Study:

• To investigate the distinct heparin sensitivities of two thrombin forms, Ts-thrombin and Tp-thrombin.
• To characterize the differential effects of heparin on thrombin inactivation and stability.

Main Methods:

• Heparin-facilitated inactivation assays using antithrombin-III.
• Sephadex G-200 gel filtration for heparin binding analysis.
• Heat inactivation assays at 54°C to assess thermal stability.

Main Results:

• Two thrombin forms, Ts-thrombin and Tp-thrombin, were identified based on heparin sensitivity.
• Heparin significantly facilitated the inactivation of Ts-thrombin by antithrombin-III, but not Tp-thrombin.
• Both thrombin forms bound to heparin, as shown by gel filtration.
• Ts-thrombin demonstrated enhanced stability and greater protection against heat inactivation by heparin compared to Tp-thrombin.

Conclusions:

• Distinct heparin sensitivities exist between Ts-thrombin and Tp-thrombin.
• Heparin differentially modulates the inactivation and stability of thrombin forms.
• These findings highlight the complex interactions between thrombin, heparin, and antithrombin-III, with implications for anticoagulant mechanisms.