Which protein provides the binding site for heparin?

Which protein provides the binding site for heparin?

• A. Protein C
• B. Protein S
• C. Factor X
• D. Antithrombin

Answer: (D)

Heparin works by binding to antithrombin, and this interaction dramatically boosts antithrombin’s ability to inactivate key clotting enzymes. When heparin binds, antithrombin undergoes a conformational change that speeds up its inhibition of thrombin and factor Xa by thousands of times, effectively preventing the conversion of fibrinogen to fibrin and stopping clot formation. Among the proteins listed, antithrombin is the molecule that provides the binding partner for heparin; the others play roles in coagulation regulation or serve as substrates but do not serve as the heparin-binding protein. Protein C and protein S are part of a separate anticoagulant pathway, while Factor X is a protease that is inhibited downstream, not the binding site for heparin itself. So the binding partner that enables heparin’s anticoagulant action is antithrombin.

Heparin works by binding to antithrombin, and this interaction dramatically boosts antithrombin’s ability to inactivate key clotting enzymes. When heparin binds, antithrombin undergoes a conformational change that speeds up its inhibition of thrombin and factor Xa by thousands of times, effectively preventing the conversion of fibrinogen to fibrin and stopping clot formation. Among the proteins listed, antithrombin is the molecule that provides the binding partner for heparin; the others play roles in coagulation regulation or serve as substrates but do not serve as the heparin-binding protein. Protein C and protein S are part of a separate anticoagulant pathway, while Factor X is a protease that is inhibited downstream, not the binding site for heparin itself. So the binding partner that enables heparin’s anticoagulant action is antithrombin.