TABLE 1.
Acid dissociation constants (pKa) for protein and nucleic acid constituents
| Residue | pKa or pKa range | Charge |
|---|---|---|
| Proteinsa | ||
| Terminal carboxyl | 2.87 | Negative |
| Aspartic acid | 3.87 | Negative |
| Glutamic acid | 4.41 | Negative |
| Cysteine | 7.56 | Negative |
| Tyrosine | 10.85 | Negative |
| Histidine | 5.64 | Positive |
| Lysine | 9.05 | Positive |
| Terminal amine | 9.09 | Positive |
| Arginine | 11.84 | Positive |
| Nucleic acidsb | ||
| Primary phosphoryl | 1 | Negative |
| Deprotonated base (G, T, U) | 9.4–10 | Negative |
| Amino group (A, C, G) | 2.3–4.6 | Positive |
a
Values from the Isoelectric Point Calculator (http://isoelectric.org/) (71).
b
Values from Blackburn (72).