1. What is Protein Concentration?

Protein concentration measurement is essential in biochemistry and molecular biology. The Beer-Lambert law relates the absorption of light to the properties of the material through which the light is traveling.

2. How Does the Calculator Work?

The calculator uses the Beer-Lambert law:

Where:

• \( Conc \) — Protein concentration (Molar)
• \( absorbance \) — Measured absorbance (AU)
• \( \epsilon \) — Molar extinction coefficient (M^-1cm^-1)
• \( path \) — Path length of the cuvette (cm)

Explanation: The equation calculates molar concentration from absorbance measurements, extinction coefficient, and path length.

3. Importance of Protein Concentration

Details: Accurate protein concentration measurement is crucial for experiments like enzyme kinetics, protein purification, and sample preparation for techniques like SDS-PAGE or Western blotting.

4. Using the Calculator

Tips: Enter absorbance (typically at 280nm), extinction coefficient (specific to your protein), and path length (usually 1 cm). Optionally include molecular weight to get concentration in mg/mL.

5. Frequently Asked Questions (FAQ)

Q1: How do I find the extinction coefficient?
A: It can be calculated from the protein sequence (using tools like ProtParam) or found in literature for known proteins.

Q2: What if my protein doesn't absorb at 280nm?
A: You may need to use alternative methods like Bradford or BCA assays that don't rely on aromatic amino acids.

Q3: Why is my calculated concentration inaccurate?
A: Possible reasons include incorrect ε value, turbid samples, or presence of other absorbing substances.

Q4: What's a typical extinction coefficient?
A: For proteins with 0.1% (1mg/mL) solution, ε is often around 1.0, but varies greatly depending on Trp/Tyr content.

Q5: Should I use this for colored proteins?
A: For proteins with chromophores (e.g., hemoglobin), use the ε at their specific absorbance maximum.