This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Gamma - Carboxylation of what requires vitamin k? 
Select and explain. 
A. Glutamine, B. Glutamic Acid, C. Glycine, D. Aspartate
B: Glutamic Acid
Answer: B: Glutamic Acid 
Explanation: Vitamin K
Function
1.   Catalyzes gamma-carboxylation of glutamic acid residues on various proteins concerned with blood clotting.
2.   Catalyzes gamma carboxylaton of glutamic acid to GABA.
Deficiency
1.   Neonatal haemorrhage with increased PT and aPTT, but normal bleeding time.
2.   Synthesized by intestinal flora, so vitamin-K deficiency can occur after the prelonged use of broad-spectrum antibiotics.
      (Note: Vitamin-K dependent clotting factors are II, VII, IX, X and protein C and S. Warfarin is a vitamin-K antagonist)
      A specific protein known as PIVKA (Protein induced in vitamin K absence) is important in diagnosing vitamin K deficiency.