Which of following amino acid has lowest iso-electric point ?

Options

A. Glycine
B. Alanine
C. Aspartic acid
D. Lysine

Answer

To determine which amino acid has the lowest isoelectric point (pI), we need to understand the concept of isoelectric point and the classification of amino acids based on their side chains.

### Step-by-Step Solution:

1. **Define Isoelectric Point (pI)**:
- The isoelectric point is the pH at which an amino acid has no net charge. This means that the number of positive charges equals the number of negative charges.

2. **Classify Amino Acids**:
- Amino acids can be classified into three categories based on their side chains:
- **Acidic Amino Acids**: These have side chains that can donate protons (H⁺) and typically have lower pI values. Examples include aspartic acid and glutamic acid.
- **Neutral Amino Acids**: These have side chains that are neither acidic nor basic. Examples include glycine and alanine. Their pI values generally range from 5.5 to 6.3.
- **Basic Amino Acids**: These have side chains that can accept protons and typically have higher pI values. Examples include lysine, arginine, and histidine. Their pI values generally range from 9 to 10.

3. **Identify the pI Values**:
- Based on experimental data:
- **Acidic Amino Acids**: pI ≈ 3
- **Neutral Amino Acids**: pI ≈ 5.5 to 6.3
- **Basic Amino Acids**: pI ≈ 9 to 10

4. **Analyze the Given Options**:
- We need to check the options provided for the amino acids:
- **Glycine**: Neutral (pI ≈ 5.5 to 6.3)
- **Alanine**: Neutral (pI ≈ 5.5 to 6.3)
- **Aspartic Acid**: Acidic (pI ≈ 3)
- **Lysine**: Basic (pI ≈ 9 to 10)

5. **Determine the Lowest pI**:
- Among the amino acids listed, aspartic acid is the only acidic amino acid, which has the lowest isoelectric point of approximately 3. The other amino acids have higher pI values.

6. **Conclusion**:
- Therefore, the amino acid with the lowest isoelectric point is **Aspartic Acid**.

### Final Answer:
The amino acid with the lowest isoelectric point is **Aspartic Acid**.