Which one of the following is the amino acid in Hb that accepts H+ and allows Hb to act as a buffer to acids?
**Core Concept**
The buffering action of hemoglobin (Hb) is a crucial aspect of its physiological function, particularly in maintaining acid-base balance in the blood. This property is attributed to the presence of specific amino acids within the Hb molecule that can accept hydrogen ions (H+) and neutralize excess acid.
**Why the Correct Answer is Right**
The amino acid responsible for this buffering action is histidine. Histidine contains an imidazole side chain, which is a weak base that can accept a proton (H+) and form a conjugate acid. This ability allows histidine to act as an effective buffer, neutralizing excess hydrogen ions and helping maintain the blood's pH. The histidine residues in Hb are located in the globin chains and are strategically positioned to accept H+ ions, thereby facilitating the buffering action of Hb.
**Why Each Wrong Option is Incorrect**
* **Option A:** Glutamic acid is an acidic amino acid, which would not be effective in accepting H+ ions to act as a buffer.
* **Option B:** Aspartic acid is another acidic amino acid, and its role is more related to the transport of ions across cell membranes rather than buffering action.
* **Option D:** Lysine is a basic amino acid but does not have the imidazole side chain necessary for accepting H+ ions and acting as a buffer.
**Clinical Pearl / High-Yield Fact**
The buffering action of Hb is an essential aspect of its physiological function, particularly in maintaining acid-base balance in the blood. The presence of histidine residues in Hb allows it to act as an effective buffer, neutralizing excess hydrogen ions and helping maintain the blood's pH.
**Correct Answer:** C.