Amino Acid pKa Values for pI Estimation
Look up the Bjellqvist pKa values used by ResidueBench, including side chains, terminal defaults, and residue-specific overrides.
Side chains and free termini
Use one contribution per eligible side chain, plus one contribution per free terminus. A terminal override applies to its terminal group. An ionizable side chain on that residue still contributes separately.
| Residue | Group type | pKa |
|---|---|---|
| K | Basic | 10.00 |
| R | Basic | 12.00 |
| H | Basic | 5.98 |
| D | Acidic | 4.05 |
| E | Acidic | 4.45 |
| C | Acidic | 9.00 |
| Y | Acidic | 10.00 |
| Terminus | Terminal residue | pKa |
|---|---|---|
| N terminus | Default | 7.50 |
| A | 7.59 | |
| E | 7.70 | |
| M | 7.00 | |
| P | 8.36 | |
| S | 6.93 | |
| T | 6.82 | |
| V | 7.44 | |
| C terminus | Default | 3.55 |
| D | 4.55 | |
| E | 4.75 |
These fixed values are specific to the selected pI model. Experimental ionization can vary with chemical environment.