Vitamin K-dependent clotting factors (II, VII, IX, X) require gamma-carboxylation of glutamate residues. The specific reaction catalysed requires vitamin K in which form?

• A Vitamin K epoxide, which provides energy for carboxylation
• B Vitamin K phylloquinone, unchanged by the reaction
• C Vitamin K hydroquinone (KH2), which is oxidised to vitamin K epoxide during gamma-carboxylation ✓
• D Vitamin K menaquinone, which is reduced by warfarin-sensitive VKOR

Explanation

Gamma-glutamyl carboxylase uses reduced vitamin K (KH2, hydroquinone form) as a cofactor; in the reaction, KH2 is oxidised to vitamin K 2,3-epoxide while glutamate is carboxylated to gamma-carboxyglutamate (Gla). Vitamin K epoxide reductase (VKOR) regenerates KH2 from epoxide — this is the warfarin target. Warfarin inhibits VKOR, depleting KH2 and impairing gamma-carboxylation, so factors lack Ca2+-binding ability.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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