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: Pathology
[{'content': 'Hb is a good buffer because of: \nSelect and explain. \nA. Histidine residues, B. Protein nature, C. Acidic nature, D. Iron molecule', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Harper mentions …‘Hemoglobin also functions in CO2 and proton transport from tissues to lungs. Release of O2 from oxy-Hb at the tissues is accompanied by uptake of protons, due to lowering of the pKa of histidine residues.’\n\nDecarboxylation of histidine to histamine is catalyzed by a broad-specificity of\xa0aromatic L-amino acid decarboxylase.\nHistidine compounds present in the human body include ergothioneine, carnosine, and dietary anserine.', 'role': 'assistant'}]