Table 1. Amino Acid pKa and pI Values188,189.
| pKa (25 °C) |
||||||
|---|---|---|---|---|---|---|
| amino acid | type | COOH | NH2 | side chain | pI (25 °C) | charge (pH 7) |
| Alanine | Neutral | 2.34 | 9.69 | 6.00 | 0 | |
| Arginine | Basic | 2.17 | 9.04 | 12.48 | 10.76 | +1 |
| Asparagine | Neutral | 2.02 | 8.80 | 5.41 | 0 | |
| Aspartic acid | Acidic | 1.88 | 9.60 | 3.65 | 2.77 | –1 |
| Cysteine | Neutral | 1.96 | 10.28 | 8.18 | 5.07 | 0 |
| Glutamic acid | Acidic | 2.19 | 9.67 | 4.25 | 3.22 | –1 |
| Glutamine | Neutral | 2.17 | 9.13 | 5.65 | 0 | |
| Glycine | Neutral | 2.34 | 9.60 | 5.97 | 0 | |
| Histidine | Basic | 1.82 | 9.17 | 6.00 | 7.95 | +1 |
| Isoleucine | Neutral | 2.36 | 9.60 | 6.02 | 0 | |
| Leucine | Neutral | 2.36 | 9.60 | 5.98 | 0 | |
| Lysine | Basic | 2.18 | 8.95 | 10.53 | 9.74 | +1 |
| Methionine | Neutral | 2.28 | 9.21 | 5.74 | 0 | |
| Phenylalanine | Neutral | 1.83 | 9.13 | 5.48 | 0 | |
| Proline | Neutral | 1.99 | 10.60 | 6.30 | 0 | |
| Serine | Neutral | 2.21 | 9.15 | 5.68 | 0 | |
| Threonine | Neutral | 2.09 | 9.10 | 5.60 | 0 | |
| Tryptophan | Neutral | 2.83 | 9.39 | 5.89 | 0 | |
| Tyrosine | Neutral | 2.20 | 9.11 | 10.07 | 5.66 | 0 |
| Valine | Neutral | 2.32 | 9.62 | 5.96 | 0 | |