Haemoglobin acts as a buffer due to the presence of

Options

A. Lysine
B. Histidine
C. Glutamine
D. Aspartic acid

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks why hemoglobin acts as a buffer. A buffer is a substance that helps maintain a stable pH in a solution, even when acids or bases are added.

2. **Identifying Components of Hemoglobin**: Hemoglobin is a protein found in red blood cells that carries oxygen. It is composed of various amino acids, including lysine, histidine, glutamic acid, and aspartic acid.

3. **Role of Histidine in Buffering**: Among the amino acids present in hemoglobin, histidine plays a crucial role in buffering. This is because histidine has a side chain that can easily gain or lose a proton (H+), allowing it to help stabilize pH levels.

4. **Concentration of Hemoglobin**: Hemoglobin is present in a higher concentration (approximately 150 g/L) compared to plasma proteins (about 70 g/L). This higher concentration enhances its ability to act as a buffer.

5. **Conclusion**: Since histidine is the amino acid responsible for the buffering capacity of hemoglobin, the correct answer to the question is option B: histidine.

**Final Answer**: Hemoglobin acts as a buffer due to the presence of histidine.

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