1. What is the Protein Concentration Formula?

The protein concentration formula estimates protein concentration from UV absorbance at 280 nm using the Beer-Lambert law. This method is based on the absorbance of aromatic amino acids (tryptophan and tyrosine) in proteins.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( C \) — Protein concentration (mg/mL)
• \( A_{280} \) — Absorbance at 280 nm (AU)
• \( \varepsilon \) — Extinction coefficient (mL/mg/cm)
• \( l \) — Path length of the cuvette (cm)

Explanation: The absorbance is directly proportional to the protein concentration, extinction coefficient, and path length.

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration measurement is essential for protein purification, enzyme kinetics studies, protein-protein interaction studies, and biochemical assays.

4. Using the Calculator

Tips:

• Measure absorbance at 280 nm using a spectrophotometer
• Use the extinction coefficient specific to your protein
• Standard cuvettes typically have 1 cm path length
• For dilute samples, use a shorter wavelength (205 nm) for better sensitivity

5. Frequently Asked Questions (FAQ)

Q1: How do I find the extinction coefficient for my protein?
A: You can calculate it from the amino acid sequence using online tools like ProtParam or find it in literature for known proteins.

Q2: Why use 280 nm for protein measurement?
A: Tryptophan and tyrosine residues absorb strongly at 280 nm, making it a convenient wavelength for most proteins.

Q3: What if my protein doesn't contain tryptophan or tyrosine?
A: Use alternative methods like Bradford assay, BCA assay, or measure at 205 nm where peptide bonds absorb.

Q4: How accurate is this method?
A: It's generally accurate to ±10% if the extinction coefficient is known. Accuracy depends on protein composition and sample purity.

Q5: What's a typical extinction coefficient for proteins?
A: Most proteins have ε values between 0.5-2.0 mL/mg/cm. Antibodies typically have higher values (~1.4 mL/mg/cm).