Amino acid responsible for buffering action of Hemoglobin is?

ANSWER: (A) HistidineREF: Ganong22nd edition chapter 39, Fluid Electrolyte & Acid Base by Jack L. Keyes page 80 table 5-1, Understanding Acid-Base by Benjamin Abelow page 41As with hemoglobin, the most important buffering sites of the plasma proteins are the side groups of histidine. Thus, conceptually, it would not be wrong to consider hemoglobin and plasma proteins as a single class of ''histidine buffers"COMPARTMENT WISE BUFFER SYSTEMS ARE:CompartmentMajor bufferECFBloodPlasmaPlasma proteinsRBCHemoglobinInterstitial fluid BicarbonateIGF Phosphate > ProteinsNOTE: Bicarbonate is the predominant buffer of ECF as a wholeHemoglobin is the predominant buffer of blood as a whole because hemoglobin is present in large amounts the hemoglobin in blood has six times the buffering capacity of the plasma proteinsAlthough hemoglobin is intracellular (inside RBC), it is often considered ECF buffer because RBC is a cellular component of ECF and because of the cellular permeability of RBC membrane.