Hen egg lysozyme
A soluble enzyme with four disulfide bonds.
Protein Molecular Weight Calculator
FigranPaste a sequence to get molecular weight, pI, extinction coefficient and hydropathy.
- Sequence or FASTA
- Isoelectric point (pI) and extinction coefficient
- Hydropathy plot
Protein Molecular Weight Calculator
Protein concentration from A280
- Molecular weight
- 14.31 kDa
- pI
- 9.32
- ε280 (All cystines)
- 37,970 M⁻¹ cm⁻¹
Results
| Sequence name | Length | MW average (Da) | pI | Molar extinction coefficient (M⁻¹ cm⁻¹) | Instability index | Aliphatic index | GRAVY |
|---|---|---|---|---|---|---|---|
| 129 | 14,313.14 | 9.32 | 37,970 | 16.09 (stable, predicted) | 65.12 | −0.472 |
- Length
- 129
- Molecular formula
- C613H959N193O185S10
- Net charge at pH 7.4
- 7.38
- Molar extinction coefficient (M⁻¹ cm⁻¹) (Reduced)
- 37,470
- Molar extinction coefficient (M⁻¹ cm⁻¹) (All cystines)
- 37,970
- Abs 0.1%
- 2.653
- Instability index
- 16.09 (stable, predicted)
- Aliphatic index
- 65.12
- Mass with 4 disulfides
- 14,305.08 Da
Estimated half-life
- Mammalian reticulocytes, in vitro
- 1.3 h
- Yeast, in vivo
- 3 min
- E. coli, in vivo
- 3 min
N-end rule prediction; not applicable to modified N termini.
Amino acid counts
- A
- 12
- C
- 8
- D
- 7
- E
- 2
- F
- 3
- G
- 12
- H
- 1
- I
- 6
- K
- 6
- L
- 8
- M
- 2
- N
- 14
- P
- 2
- Q
- 3
- R
- 11
- S
- 10
- T
- 7
- V
- 6
- W
- 6
- Y
- 3
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How to calculate protein parameters
Calculate molecular weight of protein from amino acid sequence in four steps.
1Paste a sequence
Enter one sequence or multiple FASTA records.
2Trim residues
Remove a tag or signal peptide if needed.
3Read the results
Compare mass, pI and other properties.
4Download
Save the selected plot or the results table.
How to read a hydropathy plot
Hydropathy analysis averages residues in a sliding window. Choose 9 residues for local detail or 19 for broader membrane-scale patterns. Peaks above 1.6 can suggest hydrophobic membrane-spanning segments; they do not establish topology.
How the values are calculated
Mass sums residue masses and water. The theoretical isoelectric point (pI) is the pH at which the Bjellqvist model predicts zero net charge. Extinction uses Trp, Tyr and paired cysteines; modifications are excluded.
Bjellqvist pKa values
| Ionizable group | pKa |
|---|---|
| N terminus (default) | 7.50 |
| C terminus (default) | 3.55 |
| K | 10.00 |
| R | 12.00 |
| H | 5.98 |
| D | 4.05 |
| E | 4.45 |
| C | 9.00 |
| Y | 10.00 |
The N-terminal pKa depends on the first residue.
Extinction contributions at 280 nm (M⁻¹ cm⁻¹)
| W | 5,500 |
|---|---|
| Y | 1,490 |
| Cystine pair | 125 |
References: Bjellqvist et al. (1993) · Pace et al. (1995) · Kyte and Doolittle (1982) · Guruprasad et al. (1990) · Gasteiger et al. (2005) · Ikai (1980) · UniProt example sequences (CC BY 4.0)
Protein molecular weight FAQ
How is protein molecular weight calculated?
Add the masses of the amino acid residues and one water molecule. The result describes the unmodified sequence.
How do Da and kDa relate?
One kDa equals 1,000 Da. This protein kDa calculator displays both units for the same molecular mass.
Why does SDS-PAGE differ?
Migration also depends on protein shape, modifications and experimental conditions.
What is pI, and how exact is it?
The pI is the pH where the model predicts zero net charge, not an exact measurement. Bjellqvist pKa values were derived from immobilized pH gradient gels with 9.2–9.8 M urea across pH 4.5–7.3. The model ignores folding and treats cysteines as free; highly basic proteins and small peptides may be less accurate. Different tools use different pKa scales and can disagree. The default lysozyme example has a calculated pI of 9.32.
How is A280 converted to concentration?
The Beer–Lambert relationship uses the extinction coefficient and optical path length. Other absorbing substances can affect the measurement.
Which cysteine state should I choose?
Choose reduced for free thiols or all cystines for the paired-disulfide approximation. Actual bond formation can differ.
Does this match ExPASy ProtParam?
Mass, pI, extinction, GRAVY and aliphatic index follow ExPASy ProtParam conventions. For U, O, B, Z or X, this tool does not report an instability index.
How do tags, disulfides and phosphorylation change mass?
A His6 tag adds about 822.85 Da average mass, each disulfide removes about 2.016 Da, and phosphorylation adds about 79.98 Da average or 79.97 Da monoisotopic mass. Glycosylation has no fixed mass. The main sequence mass does not include these modifications.
Is my sequence uploaded?
No. Calculations run locally in your browser.