Identify the protein that binds to and increases the half-life of factor VIII; it unbinds from factor VIII when factor VIII is activated by thrombin.

Identify the protein that binds to and increases the half-life of factor VIII; it unbinds from factor VIII when factor VIII is activated by thrombin.

• A. Factor IX
• B. Von Willebrand factor
• C. Factor VIII
• D. Factor X

Answer: (B)

Von Willebrand factor serves as the carrier for factor VIII in the bloodstream, binding and shielding it from rapid clearance and proteolysis to increase its half-life. When thrombin activates factor VIII to factor VIIIa, the bond to von Willebrand factor weakens and the factor VIIIa dissociates, freeing it to participate in the intrinsic tenase complex with factor IXa on a platelet surface to accelerate activation of factor X. Clinically, a deficiency or defect in von Willebrand factor reduces factor VIII stability and contributes to bleeding tendency.

Von Willebrand factor serves as the carrier for factor VIII in the bloodstream, binding and shielding it from rapid clearance and proteolysis to increase its half-life. When thrombin activates factor VIII to factor VIIIa, the bond to von Willebrand factor weakens and the factor VIIIa dissociates, freeing it to participate in the intrinsic tenase complex with factor IXa on a platelet surface to accelerate activation of factor X. Clinically, a deficiency or defect in von Willebrand factor reduces factor VIII stability and contributes to bleeding tendency.