1. What is the Protein Concentration Equation?

The protein concentration equation estimates protein concentration from absorbance at 280nm (A₂₈₀), accounting for sample dilution and the protein's extinction coefficient. This is based on the Beer-Lambert law and the UV absorbance of aromatic amino acids.

2. How Does the Calculator Work?

The calculator uses the protein concentration equation:

Where:

• \( A_{280} \) — Absorbance at 280nm (dimensionless)
• \( dilution\_factor \) — How much the sample was diluted (dimensionless)
• \( \epsilon \) — Extinction coefficient (mL/(mg·cm))

Explanation: The equation calculates protein concentration based on UV absorbance of tryptophan and tyrosine residues at 280nm, corrected for any sample dilution and the specific absorbance characteristics of the protein.

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. It ensures proper loading for SDS-PAGE and other analytical techniques.

4. Using the Calculator

Tips: Enter A₂₈₀ value (typically between 0.1-1.0 for accurate measurement), the dilution factor (1 if undiluted), and the extinction coefficient (specific to your protein). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What if I don't know the extinction coefficient?
A: You can estimate it from the protein sequence (0.1% solution has A₂₈₀ ≈ 1.0 for most proteins) or measure it experimentally.

Q2: Why measure at 280nm?
A: Tryptophan and tyrosine absorb strongly at this wavelength, while other biomolecules typically don't interfere.

Q3: What are typical extinction coefficients?
A: They vary widely (e.g., 0.5-2.0 mL/(mg·cm)) depending on the protein's aromatic amino acid content.

Q4: Are there limitations to this method?
A: Less accurate for proteins with few aromatic residues or samples with nucleic acid contamination (which also absorb at 280nm).

Q5: Should I use a quartz cuvette?
A: Yes, plastic cuvettes may absorb at 280nm. Use quartz for UV measurements.