1. What is the Protein Extinction Coefficient?

The protein extinction coefficient at 280 nm (ε₂₈₀) quantifies how strongly a protein absorbs light at 280 nm wavelength. This measurement is crucial for determining protein concentration using UV spectrophotometry.

2. How Does the Calculator Work?

The calculator uses the extinction coefficient equation:

Where:

• \( W \) — Number of tryptophan residues
• \( Y \) — Number of tyrosine residues
• \( C \) — Number of cystine (disulfide bond) residues

Explanation: The equation accounts for the contribution of aromatic amino acids (tryptophan and tyrosine) and disulfide bonds to UV absorption at 280 nm.

3. Importance of Extinction Coefficient Calculation

Details: Accurate extinction coefficient calculation is essential for determining protein concentration, monitoring protein purification, and conducting various biochemical assays.

4. Using the Calculator

Tips: Enter the number of tryptophan, tyrosine, and cystine residues in your protein. All values must be non-negative integers.

5. Frequently Asked Questions (FAQ)

Q1: Why are these specific amino acids used in the calculation?
A: Tryptophan and tyrosine have strong absorption at 280 nm due to their aromatic rings, and cystine (disulfide bonds) contributes weakly to absorption.

Q2: What are typical extinction coefficient values?
A: Values typically range from thousands to hundreds of thousands M⁻¹cm⁻¹, depending on the protein's size and aromatic amino acid content.

Q3: When should this calculation be used?
A: This calculation is used when you need to determine protein concentration using UV absorbance at 280 nm.

Q4: Are there limitations to this equation?
A: The equation assumes standard conditions and may be less accurate for proteins with unusual amino acid compositions or in non-standard buffer conditions.

Q5: Can this be used for all proteins?
A: While generally applicable, proteins with chromophores or unusual modifications may require additional considerations.