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Protein extinction coefficient at 280 nm
The molar extinction coefficient at 280 nm by Pace et al. 1995, with all cysteines paired and all reduced, and the absorbance of a 1 g/L solution.
Sequence
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Answer
ε280
The molar extinction coefficient at 280 nm by Pace et al.
More about this
1995, with all cysteines paired and all reduced, and the absorbance of a 1 g/L solution.
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Worked example
- GFP (P42212, 238 residues): 1 Trp, 11 Tyr and 2 Cys give ε280 = 22,015 M⁻¹cm⁻¹ with every cysteine paired and 21,890 with every cysteine reduced (Pace et al. 1995).
- A 1 g/L solution reads A280 = 22015 / 26886.32 = 0.819 at 1 cm.
- A protein without Trp, Tyr or Cys has no ε280 by this method and the card says so.
Method
ε280 = 5,500·nTrp + 1,490·nTyr + 125·n(cystine); A280(1 g/L) = ε280 / MW
- Molar extinction coefficient at 280 nm. Pace CN, Vajdos F, Fee L, Grimsley G, Gray T. How to measure and predict the molar absorption coefficient of a protein. Protein Sci 1995;4:2411-2423 (read 5 October 2026).Checked against Expasy ProtParam exactly on 22 sequences in both cysteine conventions (6 October 2026). ProtParam is a tool of the SIB Swiss Institute of Bioinformatics; not affiliated.
- Average molecular weight from the sequence. ExPASy ProtParam (Gasteiger et al. 2005); the fixtures are ProtParam's printed weights, retrieved 5 October 2026.Checked against Expasy ProtParam within 0.01 Da on 22 sequences with ProtParam's residue masses (6 October 2026). ProtParam is a tool of the SIB Swiss Institute of Bioinformatics; not affiliated.
Constants
- pace-1995: Pace et al. 1995 coefficients: 5,500 Trp, 1,490 Tyr, 125 cystine
- protparam: ExPASy ProtParam average residue masses
Limits
- For research and education only, and not medical advice: nothing here is an assessment of any person's variant, sample or molecule, and a difference reported from a reference is a difference, not an interpretation.
- NCBI genetic codes 27, 28 and 31 contain context-dependent stop codons. Translation can show their amino-acid meaning, but stop-terminated translation and ORF detection are refused because the required biological context is not modelled.
- Buffer conditions you type approximate a reaction buffer, not a vendor's calculator; use the vendor's calculator for its exact value, and treat the annealing temperature as the rule of thumb it is labelled.