The blood buffer system is controlled by an amino acid of `Hb_(4)`, its chemical nature is

Options

A. acidic
B. basic
C. neutral
D. achiral

Answer

To answer the question regarding the blood buffer system controlled by an amino acid of hemoglobin (Hb4), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Amino Acid in Hemoglobin**:
- The amino acid that plays a significant role in the structure of hemoglobin is **histidine**.

2. **Understand the Role of Histidine**:
- Histidine is crucial for the buffering capacity of blood. It helps maintain the pH of blood within a narrow range, which is essential for proper physiological function.

3. **Chemical Nature of Histidine**:
- Histidine contains an **imidazole group** in its side chain. This imidazole group can accept or donate protons (H⁺ ions), which is vital for buffering.

4. **Determine the pH Influence**:
- The imidazole group of histidine is **basic in nature**. This means that it can help neutralize excess acids in the blood, contributing to the overall basicity of blood pH.

5. **Conclusion**:
- Therefore, the chemical nature of the amino acid that controls the blood buffer system in hemoglobin is **basic** due to the presence of the imidazole group in histidine.

### Final Answer:
The chemical nature of the amino acid controlling the blood buffer system in Hb4 is **basic**.