The isoelectric point (pI) of aspartic acid is 2.77 due to the presence of two carboxyl groups in its molecule.
Aspartic acid, being an acidic amino acid, possesses three ionizable groups: an α-carboxyl group, an α-amino group, and a side chain carboxyl group. The pI is the pH at which the molecule carries no net electrical charge. To calculate the pI for aspartic acid, we average the pKa values of the two carboxyl groups, since at the isoelectric point the amino acid will be protonated at the amino group and deprotonated at both carboxyl groups.
Here's how the pI is determined:
- Aspartic acid has pKa values of approximately 2.0 (α-carboxyl), 3.9 (side chain carboxyl), and 9.8 (α-amino).
- Since aspartic acid is an acidic amino acid, we average the pKa values of the two carboxyl groups to find the pI.
pI = (pKa1 + pKa2) / 2
Where:
- pKa1 = pKa of the α-carboxyl group (~2.0)
- pKa2 = pKa of the side chain carboxyl group (~3.9)
Therefore:
pI = (2.0 + 3.9) / 2 = 5.9 / 2 = 2.95
While the calculation yields 2.95, the referenced information states that the pI is 2.77. This slight discrepancy might be due to variations in experimental conditions or different sources of pKa values used.
| Feature | Value |
|---|---|
| α-carboxyl pKa | ~2.0 |
| Side chain carboxyl pKa | ~3.9 |
| α-amino pKa | ~9.8 |
| Calculated pI | 2.95 |
| Reported pI | 2.77 (Reference) |
