1. What Is The Protein Extinction Coefficient?

The extinction coefficient (ε) is a measure of how strongly a protein absorbs light at a specific wavelength. It's used to quantify protein concentration in solution using spectrophotometry.

2. How Does The Calculator Work?

The calculator uses the standard formula:

Where:

• \( nW \) — Number of tryptophan residues
• \( nY \) — Number of tyrosine residues
• \( nC \) — Number of cystine (disulfide-bonded cysteine) residues

Explanation: This formula calculates the molar extinction coefficient at 280 nm based on the aromatic amino acid content of the protein.

3. Importance Of Extinction Coefficient

Details: The extinction coefficient is essential for accurately determining protein concentration, which is critical for experiments involving enzyme kinetics, binding studies, and protein quantification.

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 only these three amino acids considered?
A: Tryptophan, tyrosine, and cystine are the primary amino acids that absorb light at 280 nm, which is the standard wavelength for protein quantification.

Q2: How accurate is this calculation?
A: This method provides a theoretical estimate. For precise measurements, experimental determination using known protein concentrations is recommended.

Q3: What if my protein has no tryptophan residues?
A: The calculation still works. Proteins without tryptophan will have a lower extinction coefficient, primarily determined by tyrosine and cystine content.

Q4: Does this work for modified amino acids?
A: No, this calculation assumes standard amino acids. Modified residues may have different absorption properties.

Q5: Can I use this for peptides as well as proteins?
A: Yes, this formula works for any polypeptide chain, regardless of size, as long as you know the amino acid composition.