The pKa Values for Ionizable Groups in Amino Acids
| Amino acid | α-COOH to α-COO– | α-NH3+ to α-NH2 | RH to R– |
|---|---|---|---|
| Glycine (Gly, G) | 2.35 | 9.78 | NA |
| Alanine (Ala, A) | 2.35 | 9.87 | NA |
| Valine (Val, V) | 2.29 | 9.74 | NA |
| Leucine (Leu, L) | 2.33 | 9.74 | NA |
| Isoleucine (Ile, I) | 2.32 | 9.76 | NA |
| Methionine (Met, M) | 2.13 | 9.28 | NA |
| Proline (Pro, P) | 1.95 | 10.64 | NA |
| Phenylalanine (Phe, F) | 2.20 | 9.31 | NA |
| Tryptophan (Trp, W) | 2.46 | 9.41 | NA |
| Serine (Ser, S) | 2.19 | 9.21 | NA |
| Threonine (Thr, T) | 2.09 | 9.10 | NA |
| Asparagine (Asn, N) | 2.14 | 8.72 | NA |
| Glutamine (Gln, Q) | 2.17 | 9.13 | NA |
| Tyrosine (Tyr, Y) | 2.20 | 9.21 | 10.46 |
| Cysteine (Cys, C) | 1.92 | 10.70 | 8.37 |
| Lysine (Lys, K) | 2.16 | 9.06 | 10.54 |
| Arginine (Arg, R) | 1.82 | 8.99 | 12.48 |
| Histidine (His, H) | 1.80 | 9.33 | 6.04 |
| Aspartic acid (Asp, D) | 1.99 | 9.90 | 3.90 |
| Glutamic acid (Glu, E) | 2.10 | 9.47 | 4.07 |