Results
Group details (fractions)
| Group | pKa | State fraction | Charge contribution |
|---|
Sample points
| pH | Net charge |
|---|
FAQs
1) How is net charge calculated?
Each ionizable group contributes according to the Henderson–Hasselbalch relation. Acidic groups contribute −fA− where fA−=1/(1+10pKa−pH). Basic groups contribute +fBH+ where fBH+=1/(1+10pH−pKa).
2) Which groups are included?
The N terminus and C terminus are always included. Side chains for Asp Glu Cys Tyr Lys Arg and His are modeled with typical literature pKa values.
3) What pKa values are used?
Default set: N 9.60; C 2.34; Asp 3.90; Glu 4.25; Cys 8.30; Tyr 10.07; Lys 10.54; Arg 12.48; His 6.04. Values are representative and context dependent.
4) What is the isoelectric point?
The pH at which the net charge equals zero. The tool finds pI by bisection over pH 0–14.
5) Why might my lab result differ?
Apparent pKa values shift with ionic strength temperature nearby charges and microenvironment. Free amino acids differ from residues inside peptides or proteins.
6) Can I change pKa values?
This version uses a fixed set for clarity. You can fork the page and edit the data table in the script to match your system.
7) Does this compute peptide charge?
No. It models a single free amino acid. Peptide charge requires counting all ionizable groups across the sequence and using residue specific pKa assumptions.
8) How is the curve generated?
The page samples pH values across your range with your chosen step size then draws a smooth SVG polyline and provides a CSV of the sampled points.