Vitamin K-dependent carboxylation activates coagulation factors II, VII, IX and X. The specific amino acid residue modified is:

• A Proline converted to hydroxyproline
• B Aspartic acid converted to beta-carboxyaspartate
• C Serine phosphorylated to phosphoserine
• D Glutamic acid converted to gamma-carboxyglutamic acid (Gla) ✓

Explanation

Vitamin K-dependent carboxylase (gamma-glutamyl carboxylase) converts specific glutamic acid (Glu) residues in the N-terminal Gla domain of coagulation factors to gamma-carboxyglutamic acid (Gla). This reaction requires vitamin K (hydroquinone form), O2 and CO2. Gla residues have two carboxylate groups on the gamma-carbon, giving them high-affinity calcium-chelating ability. Calcium binding induces conformational changes allowing Gla-domain proteins to anchor to phosphatidylserine on activated platelet membranes via calcium bridges, assembling the coagulation complexes. Warfarin inhibits vitamin K epoxide reductase (VKORC1), preventing vitamin K recycling and impairing Gla formation. Proline hydroxylation requires vitamin C; phosphoserine is a protein phosphorylation product.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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