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
Aminoacids with its PKR valve within physiological range is: 
Select and explain. 
A. Glycine, B. Histidine, C. Lysine, D. Arginine
B: Histidine
Answer: B: Histidine 
Explanation: Histidine