Study tools / Titration explorer
Titration curve explorer
Pick an amino acid to see how its charge changes as base is added. Drag the pH slider to see which form dominates.
Curve shows pH against equivalents of OH⁻ added to the fully protonated amino acid, calculated with the Henderson–Hasselbalch equation. Real curves can differ slightly with concentration and ionic strength.
pKa reference table
Values for the free amino acids at 25 °C (Lehninger, Principles of Biochemistry). In proteins, values shift with the local environment.
| Amino acid | Code | pKa₁ (α-COOH) | pKa₂ (α-NH₃⁺) | pKa (side chain) | pI |
|---|---|---|---|---|---|
| Glycine | G | 2.34 | 9.60 | 5.97 | |
| Alanine | A | 2.34 | 9.69 | 6.01 | |
| Valine | V | 2.32 | 9.62 | 5.97 | |
| Leucine | L | 2.36 | 9.60 | 5.98 | |
| Isoleucine | I | 2.36 | 9.68 | 6.02 | |
| Proline | P | 1.99 | 10.96 | 6.48 | |
| Phenylalanine | F | 1.83 | 9.13 | 5.48 | |
| Tryptophan | W | 2.38 | 9.39 | 5.88 | |
| Methionine | M | 2.28 | 9.21 | 5.75 | |
| Serine | S | 2.21 | 9.15 | 5.68 | |
| Threonine | T | 2.11 | 9.62 | 5.86 | |
| Cysteine | C | 1.96 | 10.28 | 8.18 | 5.07 |
| Tyrosine | Y | 2.20 | 9.11 | 10.07 | 5.65 |
| Asparagine | N | 2.02 | 8.80 | 5.41 | |
| Glutamine | Q | 2.17 | 9.13 | 5.65 | |
| Aspartic acid | D | 1.88 | 9.60 | 3.65 | 2.76 |
| Glutamic acid | E | 2.19 | 9.67 | 4.25 | 3.22 |
| Lysine | K | 2.18 | 8.95 | 10.53 | 9.74 |
| Arginine | R | 2.17 | 9.04 | 12.48 | 10.76 |
| Histidine | H | 1.82 | 9.17 | 6.00 | 7.58 |
Cite this page
VALREXA Biosciences. (2026, November 7). Amino acid titration curve explorer and pKa table. VALREXA Biosciences. https://valrexa.com/titration.html
APA style · Last reviewed November 7, 2026 · Our editorial standards