Protein Molar Concentration Calculator Formula

Protein Concentration Formula:

\[ C = \frac{A_{280}}{\epsilon \times l} \]

Protein Concentration (C):

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1. What is the Protein Concentration Formula?

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 determine concentration based on their extinction coefficient.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ C = \frac{A_{280}}{\epsilon \times l} \]

Where:

\( C \) — Protein concentration (mol/L)
\( A_{280} \) — Absorbance at 280nm (dimensionless)
\( \epsilon \) — Molar extinction coefficient (M^-1cm^-1)
\( l \) — Path length (cm)

Explanation: The equation calculates molar concentration from absorbance measurements, accounting for the protein's specific absorption characteristics and the cuvette path length.

3. Importance of Protein Concentration

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

4. Using the Calculator

Tips: Enter absorbance at 280nm (typically between 0.1-1.0 for accurate measurements), the protein's extinction coefficient (available in databases or calculated from sequence), and path length (usually 1cm for standard cuvettes).

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 tools like ProtParam or found in literature for well-characterized proteins.

Q2: Why use 280nm for protein measurements?
A: Tryptophan and tyrosine residues absorb strongly at 280nm, making it a convenient wavelength for protein detection.

Q3: What if my protein has no tryptophan?
A: For proteins lacking tryptophan, 205nm can be used to detect peptide bonds, but this requires a different extinction coefficient.

Q4: How accurate is this method?
A: Accuracy depends on knowing the correct extinction coefficient. For purified proteins with known coefficients, accuracy is typically ±5-10%.

Q5: What about interfering substances?
A: Nucleic acids and certain buffers can interfere. A 260/280 ratio can help assess nucleic acid contamination.