Vitamin K is essential for the post-translational modification of clotting factors II, VII, IX, and X. Which specific modification does vitamin K facilitate?

• A Phosphorylation of serine residues
• B Hydroxylation of proline residues
• C Gamma-carboxylation of glutamate residues ✓
• D N-linked glycosylation of asparagine residues

Explanation

Vitamin K serves as a cofactor for gamma-glutamyl carboxylase, which carboxylates specific glutamate residues in the N-terminal Gla domains of clotting factors II (prothrombin), VII, IX, X, and anticoagulant proteins C and S. Gamma-carboxyglutamate (Gla) residues chelate calcium ions (Ca2+), enabling the clotting factors to bind to negatively charged phospholipid surfaces on activated platelets, a prerequisite for coagulation cascade activation. Warfarin inhibits vitamin K epoxide reductase, blocking recycling of vitamin K and impairing this carboxylation.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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