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: Biochemistry
[{'content': 'In carboxylation of clotting factors by Vitamin K, which amino acid is carboxylated: \nSelect and explain. \nA. Glutamate, B. Aspaate, C. Histamine, D. Histidine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Glutamate', 'role': 'assistant'}]