Extinction Coefficient Calculator

Calculate the molar extinction coefficient at 280 nm from an amino acid sequence using the Pace method, and convert absorbance readings to protein/peptide concentration via Beer-Lambert law.

Section 1: Extinction Coefficient from Sequence

Preset peptides

Amino acid sequence (single-letter codes)

Conditions

Disulfide bonds(auto: 1)

Residues parsed

30 amino acids

Parsed sequence: FVNQHLCGSHLVEALYLVCGERGFFYTPKT

Extinction Coefficient (280 nm)

3,105M⁻¹ cm⁻¹

Native/oxidized conditions

Absorptivity (A 0.1%)

0.905(mg/mL)⁻¹ cm⁻¹

= extinction / molecular weight

Molecular Weight

3429.96Da

Average isotopic mass

Tryptophan (W)

0residues

Contributes 5,500 M⁻¹cm⁻¹ each

Tyrosine (Y)

2residues

Contributes 1,490 M⁻¹cm⁻¹ each

Cysteine (C)

2residues (1 S-S bonds)

Each S-S bond contributes 125 M⁻¹cm⁻¹

Calculation (Pace method)

ε₂₈₀ = (0 Trp × 5500) + (2Tyr × 1490) + (1 S-S × 125) = 3,105 M⁻¹ cm⁻¹

Section 2: Absorbance to Concentration (Beer-Lambert)

Absorbance (A280)

Path length (cm)

Extinction coefficient (M⁻¹cm⁻¹)(from Sec. 1)

Dilution factor

Formula: c = (A × dilution factor) / (ε × path length)

Molar Concentration

3.221e-4M

Millimolar

0.3221mM

Micromolar

322.06µM

Mass Concentration

1.1047mg/mL

About this calculator

Extinction coefficients are estimated using the Pace method (Pace et al., 1995) based on the number of Trp, Tyr, and Cys (disulfide) residues. Actual values may differ due to protein folding, solvent effects, post-translational modifications, or non-standard amino acids. This tool is for educational and research reference only.

Extinction Coefficient Calculator

Section 1: Extinction Coefficient from Sequence

Section 2: Absorbance to Concentration (Beer-Lambert)

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Extinction Coefficient Calculator

Section 1: Extinction Coefficient from Sequence

Section 2: Absorbance to Concentration (Beer-Lambert)