Table 1.
Measured pKa values of α-amino and α-carboxyl groups of all twelve α-amino acids with non-ionizable side chains (±standard deviation, SD). All pKa values were determined using the same equipment, reagents and procedures as detailed in Material and Methods.
| Amino Acid | α-NH3+ | α-COOH |
|---|---|---|
| Ala | 9.80 ± 0.02 | 2.40 ± 0.04 |
| Val | 9.55 ± 0.01 | 2.33 ± 0.05 |
| Gly | 9.68 ± 0.01 | 2.40 ± 0.04 |
| Ile | 9.69 ± 0.01 | 2.38 ± 0.04 |
| Leu | 9.64 ± 0.01 | 2.35 ± 0.04 |
| Gln | 9.15 ± 0.01 | 2.22 ± 0.05 |
| Met | 9.15 ± 0.02 | 2.24 ± 0.05 |
| Ser | 9.11 ± 0.02 | 2.25 ± 0.05 |
| Thr | 9.01 ± 0.01 | 2.23 ± 0.05 |
| Asn | 8.80 ± 0.02 | 2.19 ± 0.05 |
| Phe | 9.15 ± 0.03 | 2.23 ± 0.05 |
| Trp | 9.42 ± 0.02 | 2.35 ± 0.04 |