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Old 03-02-2011
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Arrow Test your knowledge #26! (Coagulation)

Heparin binds to Antithrombin III (ATIII) and dramatically accelerates its enzymatic activity. As a serine protease inhibitor, ATIII-heparin can inactivate the serine proteases of the intrinsic pathway, XIIIa, XIa, IXa, and Xa - but what is its primary anti-coagulative activity?
  1. ATIII stimulates the release of plasminogen activators from tissues
  2. Activated ATIII dissolves the cross-linking of fibrin by proteolysis
  3. ATIII catalyses the binding of thrombin to thrombomodulin, allowing Protein C to be activated
  4. One molecule of ATIII inactivates one molecule of thrombin; heparin is catalytic
  5. Plasmin is cleaved from plasminogen by ATIII
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Old 03-02-2011
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Default i think it is c

c is my ans
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Old 03-02-2011
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Default D.

One molecule of ATIII inactivates one molecule of thrombin; heparin is catalytic
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Old 03-02-2011
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Arrow D) One molecule of ATIII inactivates one molecule of thrombin; heparin is catalytic

My ans is D) One molecule of ATIII inactivates one molecule of thrombin; heparin is catalytic.

heparin-AT complex mainly acts on intrinsic pathway of coagulation, especially on factors XIIIa, XIa, IXa, and Xa. Heparin binds on AT-III to activates the inhibitory effect on the clotting factors.

"One molecule of ATIII inactivates one molecule of thrombin" .... I don't know anything about the ratio...
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Default

My answer C
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Default D

D) ATIII binds directly to Thrombin and inactivates it. Heparin catalyzes this function
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Old 03-02-2011
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Correct Answer Correct!

D is correct: one molecule of ATIII inactivates one molecule of thrombin; heparin is catalytic, and can quickly bind to another ATIII.
  • Bradykinin and thrombin, among other agents, stimulate the release of plasminogen activators from tissues (A).
  • Fibrin is digested by plasmin (B).
  • ATIII does not catalyse the binding of thrombin to thrombomodulin (C); however, thrombin does activate Protein C, and this is greatly enhanced with thrombomodulin.
  • Plasminogen activators convert plasminogen to active plasmin (E).
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