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
Most stable amino acid at the physiological pH is 
Select and explain. 
A. Histidine, B. Lysine, C. Arginine, D. Glycine
A: Histidine
Answer: A: Histidine 
Explanation: As histidine titrates in the physiological pH range it remains stable.