Which of the following amino acids have very low isoelectric pH value (lower than 5) ?

Options

A. Histidine
B. Aspartic acid
C. Glutamic acid
D. Arginine

Explanation

To determine which amino acids have a very low isoelectric pH value (lower than 5), we will analyze the isoelectric points (pI) of the given amino acids: histidine, aspartic acid, glutamic acid, and arginine.

### Step-by-Step Solution:

1. **Understand Isoelectric Point (pI)**:
- The isoelectric point is the pH at which an amino acid exists in a neutral form (zwitterion) and does not migrate in an electric field. It is influenced by the side chain of the amino acid.

2. **List the Amino Acids and Their Isoelectric Points**:
- Histidine: pI = 7.6
- Aspartic Acid: pI = 2.277
- Glutamic Acid: pI = 3.25
- Arginine: pI = 10.76

3. **Identify the pI Values Lower than 5**:
- Histidine (7.6) > 5
- Aspartic Acid (2.277) < 5
- Glutamic Acid (3.25) < 5
- Arginine (10.76) > 5

4. **Determine Which Amino Acids Have Very Low pI Values**:
- From the above, aspartic acid and glutamic acid have pI values lower than 5. However, since the question specifies "very low," we can conclude that aspartic acid, with the lowest pI value of 2.277, is the most relevant answer.

5. **Final Conclusion**:
- The amino acids with very low isoelectric pH values (lower than 5) are **aspartic acid** and **glutamic acid**, but the one with the lowest pI is **aspartic acid**.

### Final Answer:
- **Aspartic Acid** is the amino acid with a very low isoelectric pH value (lower than 5).