Which vitamin K-dependent factors include II, VII, IX, X and proteins C and S?

• A. Factors II, VII, IX, X
• B. Factors II, VII, IX, X and proteins C and S
• C. Factor XIII and VII
• D. Factors V and VIII

Answer: (B)

Vitamin K enables gamma-carboxylation of certain coagulation proteins, which allows them to bind calcium and function in the clotting process. The factors that require this modification are II (prothrombin), VII, IX, and X, along with the anticoagulant proteins C and S that help regulate coagulation. Factor XIII does not depend on vitamin K for its function, as it acts later to crosslink fibrin. Similarly, factors V and VIII are not vitamin K–dependent cofactors. Therefore, the correct set includes II, VII, IX, X and proteins C and S.