1. What is the Protein Concentration Equation?

The Beer-Lambert law relates the absorption of light to the properties of the material through which the light is traveling. For proteins, absorbance at 280nm is commonly used to estimate concentration.

2. How Does the Calculator Work?

The calculator uses the Beer-Lambert law equation:

Where:

• \( C \) — Protein concentration (mg/ml)
• \( A \) — Absorbance at 280nm (dimensionless)
• \( \varepsilon \) — Extinction coefficient (ml mg^-1 cm^-1)
• \( l \) — Pathlength (cm)

Explanation: The equation calculates protein concentration based on how much light the protein solution absorbs at 280nm wavelength.

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration measurement is essential for experimental reproducibility, protein purification, enzymatic assays, and biochemical experiments.

4. Using the Calculator

Tips: Enter absorbance at 280nm, extinction coefficient for your protein, and pathlength of the cuvette. Standard pathlength is 1cm. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How do I find the extinction coefficient for my protein?
A: The extinction coefficient can be calculated from the protein sequence using online tools like ProtParam or obtained from literature.

Q2: Why use 280nm for protein concentration?
A: Tryptophan and tyrosine residues absorb light at 280nm, making this wavelength useful for protein quantification.

Q3: What if my protein doesn't have tryptophan or tyrosine?
A: Alternative methods like Bradford or BCA assay should be used for proteins lacking these residues.

Q4: What is a typical extinction coefficient?
A: This varies greatly by protein. For example, IgG antibodies have ε ~1.4, while lysozyme has ε ~2.6.

Q5: How accurate is this method?
A: Accuracy depends on knowing the correct ε value and having a pure protein sample. Contaminants that absorb at 280nm will affect results.