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
Hemoglobin acts as a buffer because of: 
Select and explain. 
A. Glycine, B. Histidine, C. Alanine, D. Valine
B: Histidine
Answer: B: Histidine 
Explanation: Heamoglobin has 4 polypeptide chains, two identical a- chains and two identical p chains.Iron (Fe2+) of Hb is bound to histidine & four pyrrole rings.