1. What is the Protein Extinction Coefficient?

The extinction coefficient measures how strongly a protein absorbs light at a specific wavelength. It is used to quantify protein concentration in solution using spectrophotometry, particularly at 280 nm where aromatic amino acids absorb light.

2. How Does the Calculator Work?

The calculator uses the extinction coefficient equation:

Where:

• \( n_{Trp} \) — Number of tryptophan residues
• \( n_{Tyr} \) — Number of tyrosine residues
• \( n_{Cys} \) — Number of cysteine residues

Explanation: The equation calculates the molar extinction coefficient at 280 nm based on the contribution of aromatic amino acids in the protein sequence.

3. Importance of Extinction Coefficient Calculation

Details: Accurate extinction coefficient calculation is essential for determining protein concentration, which is crucial for biochemical experiments, protein purification, and quantitative analysis.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: Why are only Trp, Tyr, and Cys considered?
A: These three amino acids have significant absorbance at 280 nm due to their aromatic rings and disulfide bonds.

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 amino acid composition.

Q3: How accurate is this calculation method?
A: This method provides a good estimate, but actual values may vary due to protein folding and local environment effects.

Q4: Can this be used for modified proteins?
A: For proteins with modified aromatic residues, experimental determination may be necessary for accurate results.

Q5: What units are used for the extinction coefficient?
A: The extinction coefficient is expressed in M⁻¹cm⁻¹ (molar absorptivity).