Calculate Protein Concentration From Absorbance

Protein Concentration Formula:

\[ Conc = \frac{Abs}{\varepsilon \times l} \]

Protein Concentration (Conc):

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1. What is the Protein Concentration Formula?

The Beer-Lambert law is used to calculate protein concentration from absorbance measurements. This formula 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 formula:

\[ Conc = \frac{Abs}{\varepsilon \times l} \]

Where:

\( Conc \) — Protein concentration (mg/mL)
\( Abs \) — Absorbance measured at specific wavelength (AU)
\( \varepsilon \) — Extinction coefficient (mL/(mg·cm))
\( l \) — Path length of the cuvette (cm)

Explanation: The formula calculates protein concentration based on the amount of light absorbed by the protein solution, adjusted for the protein's specific extinction coefficient and the path length of the measurement.

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration measurement is essential for various biochemical experiments, including enzyme kinetics studies, protein purification, and quantitative western blotting.

4. Using the Calculator

Tips: Enter absorbance value (typically measured at 280nm), the extinction coefficient for your specific protein, and the path length of your cuvette (usually 1.0 cm). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical extinction coefficient for proteins?
A: For proteins with tryptophan and tyrosine, ε is approximately 1.0 mL/(mg·cm) at 280nm, but it varies significantly between different proteins.

Q2: Why measure at 280nm?
A: 280nm is the wavelength where tryptophan and tyrosine residues absorb light, making it ideal for protein concentration measurements.

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

Q4: How accurate is this method?
A: The accuracy depends on knowing the correct extinction coefficient for your specific protein and ensuring the sample is free of contaminants that absorb at 280nm.

Q5: Can I use this for any concentration range?
A: The Beer-Lambert law is generally valid for absorbance values between 0.1 and 1.0. Samples outside this range should be diluted or concentrated accordingly.