Calculadora de Beer-Lambert para Proteínas Gratis
Calcula la concentración de proteínas por absorbancia UV a 280 nm usando coeficientes de extinción.
Mass Concentration
0.0010 mg/mL
Mass Concentration vs Absorbance at 280 nm
Fórmula
## Protein Concentration from A280 UV absorbance at 280 nm is widely used to measure protein concentration. Aromatic residues (Trp, Tyr) and disulfide bonds absorb at this wavelength. ### Formula **c (M) = A280 / (epsilon × l)** **c (mg/mL) = c (M) × MW / 1000** The extinction coefficient epsilon can be calculated from the amino acid sequence using tools like ProtParam. Typical values range from 10,000 to 100,000 M⁻¹cm⁻¹.
Ejemplo Resuelto
A protein with epsilon = 43,000 M⁻¹cm⁻¹ and MW = 45 kDa, measured A280 = 1.0 in a 1 cm cuvette.
- 01c = 1.0 / (43000 × 1) = 2.326 × 10⁻⁵ M = 23.26 uM
- 02c = 23.26 × 10⁻⁶ × 45000 / 1000 = 1.047 mg/mL
Preguntas Frecuentes
What if my protein has no tryptophan?
Proteins with no Trp have very low A280 extinction coefficients (only from Tyr and Cys). The measurement becomes less sensitive. Consider using BCA or Bradford assays instead, or measure at 205 nm (peptide bond absorption).
How accurate is A280 measurement?
Very accurate for pure proteins with known extinction coefficients. Contaminating nucleic acids absorb at 260 nm and can be corrected using the A260/A280 ratio. Pure protein has A260/A280 around 0.55-0.6.
What is the A280 0.1% convention?
Some references report E0.1% = absorbance of a 1 mg/mL solution in a 1 cm path. To convert: epsilon (M⁻¹cm⁻¹) = E0.1% × MW / 10.
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