1. What is Protein Concentration Calculation?

Protein concentration calculation using UV absorbance is a common method in biochemistry to determine the concentration of protein solutions. This method relies on the Beer-Lambert law and the specific extinction coefficient of the protein.

2. How Does the Calculator Work?

The calculator uses the protein concentration formula:

Where:

• Absorbance — Measured UV absorbance at 280nm (unitless)
• Extinction coefficient — Protein-specific coefficient (mL/(mg·cm))

Explanation: The formula calculates protein concentration based on the linear relationship between absorbance and concentration as described by the Beer-Lambert law.

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration measurement is essential for various biochemical applications including protein purification, enzyme kinetics studies, protein-protein interaction assays, and preparation of samples for electrophoresis and chromatography.

4. Using the Calculator

Tips: Enter the measured absorbance value and the extinction coefficient for your specific protein. Both values must be positive numbers. The extinction coefficient is protein-specific and can typically be found in literature or calculated from the protein's amino acid sequence.

5. Frequently Asked Questions (FAQ)

Q1: Why measure protein concentration at 280nm?
A: Proteins absorb UV light at 280nm due to the presence of tryptophan and tyrosine residues, making this wavelength ideal for concentration measurements.

Q2: How do I find the extinction coefficient for my protein?
A: The extinction coefficient can be calculated from the protein's amino acid sequence using online tools or found in published literature for well-characterized proteins.

Q3: What are typical extinction coefficient values?
A: Extinction coefficients typically range from 0.5 to 2.0 mL/(mg·cm) for most proteins, but can vary significantly depending on the specific protein.

Q4: Are there limitations to this method?
A: This method assumes the protein is pure and may be inaccurate if nucleic acids or other UV-absorbing contaminants are present. It's also less accurate for proteins with few aromatic amino acids.

Q5: What other methods exist for protein concentration measurement?
A: Other methods include Bradford assay, BCA assay, Lowry assay, and quantitative amino acid analysis, each with their own advantages and limitations.