Extinction Coefficient Calculator

The extinction coefficient is calculated using the sum of individual amino acid contributions, primarily from tryptophan (5500 M⁻¹cm⁻¹), tyrosine (1490 M⁻¹cm⁻¹), and cysteine disulfide bonds (125 M⁻¹cm⁻¹) at 280 nm. The formula accounts for the number of each chromophore in the protein sequence. See also our Brillouin Index Calculator.

280 nm is the standard wavelength for protein absorption measurements as it corresponds to the absorption maximum of aromatic amino acids. Some applications may use 205 nm for peptide bond absorption or other wavelengths for specific chromophores.

Extinction coefficients vary based on the content of aromatic amino acids (tryptophan, tyrosine) and disulfide bonds. Proteins rich in these residues will have higher extinction coefficients, while those with few or no aromatic residues will have lower values.

This method provides theoretical extinction coefficients based on individual amino acid contributions. Actual values may vary by ±10-15% due to environmental effects, protein folding, and interactions between chromophores in the native structure. You might also find our Species Evenness Calculator useful.

Yes, this calculation assumes denatured conditions where amino acid residues behave independently. For native proteins, the calculated value serves as an approximation, though local environment effects may cause slight variations.

This calculator only recognizes the 20 standard amino acids. Non-standard amino acids, modifications, or unusual residues are ignored in the calculation. For modified proteins, manual adjustment may be necessary.

The molecular weight is calculated by summing the average molecular weights of all amino acids and subtracting water molecules lost during peptide bond formation. This gives the theoretical molecular weight of the mature protein.