This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins and Minerals, Subject name: Biochemistry
Which one of the following amino acid residue is carboxylated by Vitamin K? 
Select and explain. 
A. Aspaate, B. Glutamate, C. Tryptophan, D. Tyrosine
B: Glutamate
Answer: B: Glutamate 
Explanation: Vitamin K is the cofactor for g-carboxylation of glutamate residues of protein to produce g-carboxy glutamate (gla). This process is known as Vitamin K epoxide cycle (as illustrated in the image below).