Extinction Coefficient

Calculate the extinction coefficient of protein sequences. Upload a FASTA file or paste your protein sequences below to get the extinction coefficient values.

Input (Protein sequences)

FASTA

Click to upload or drag and drop

FASTA file (.fasta, .fas, .fa, .txt)

Max size: 50MB

Calculation options

Wavelength (nm)

280 nm

Standard protein absorption (Trp, Tyr, Cys)

276 nm

Alternative wavelength

205 nm

Deep UV (peptide bond absorption)

Calculation method

Different methods use slightly different extinction coefficients

Cysteine oxidation state

Reduced cysteines

All cysteine residues are reduced (free sulfhydryl groups)

Oxidized cysteines

Cysteines form disulfide bonds (cystines)

Include absorbance at 0.1% (1 g/L)(normalized by molecular weight)

Extinction coefficient (M⁻¹cm⁻¹)

Numbers

About extinction coefficient calculation

Extinction coefficients predict how much light a protein absorbs:

• Units: M⁻¹cm⁻¹ (molar extinction coefficient)
• 280 nm: Aromatic amino acids (Trp, Tyr) + disulfide bonds
• Beer-Lambert law: A = ε × c × l
• Applications: Protein concentration determination