NADH Concentration Calculation via Beer-Lambert Law
The concentration of a substance in solution can be determined using the Beer-Lambert Law when its absorbance is known. The law relates absorbance ($A$) to the molar extinction coefficient ($\epsilon$), concentration ($c$), and path length ($l$).
The Beer-Lambert Law is stated as:
$ A = \epsilon \times c \times l $
To find the concentration ($c$), we can rearrange the formula:
$ c = \frac{A}{\epsilon \times l} $
Applying the Formula
Given values are:
- Absorbance ($A$): 0.31
- Molar extinction coefficient ($\epsilon$): $6200 \, M^{-1} cm^{-1}$
- Path length ($l$): 1 cm
Substitute these values into the rearranged formula:
$ c = \frac{0.31}{6200 \, M^{-1} cm^{-1} \times 1 \, cm} $
$ c = \frac{0.31}{6200} \, M $
Calculating Concentration
Performing the calculation:
$ c \approx 0.00005 \, M $
The question asks for the concentration in micromolar ($\mu M$). To convert from Molar ($M$) to micromolar ($\mu M$), multiply by $10^6$:
$ c \approx 0.00005 \times 10^6 \, \mu M $
$ c \approx 50 \, \mu M $
The concentration of NADH in the solution is approximately 50 $\mu M$. Correct to the nearest integer, the value is 50.
Important Questions from Enzyme Assays Molar Extinction Coefficient
- A solution shows a transmittance of 20% when taken in a cuvette of 2.5 cm path length. If the molar absorption coefficient of the solution is $12000 \text{ dm}^3/\text{mol.cm}$, the concentration of the solution is ________ $\times 10^5 \text{ mol/dm}^3$ (rounded off to two decimal places).
- A solution containing GTP has molar extinction coefficient of $1.55 \times 10^4$ $mol^{-1}dm^3cm^{-1}$ at a given wavelength. The concentration of GTP solution is $1.290 \times 10^{-5}$ $mol$ $dm^{-3}$. The absorbance of GTP solution in 1 cm cuvette at the same wavelength will be .................
- An enzyme preparation has activity of 2 Units per 20 $\mu$l, and protein concentration 0.4 mg/ml. The specific activity (Units/mg) of this enzyme will be ________
- If a $10$ mM solution of a biomolecule in a cuvette of path length $10$ mm absorbs $90\%$ of the incident light at $280$ nm, the molar extinction coefficient of the biomolecule at this wavelength is ________ $M^{-1}cm^{-1}$. (Round off to two decimal places)
- The absorbance of a $5 \times 10^{-4}$ $M$ solution of tyrosine at 280 $nm$ wavelength is 0.75. The path length of the cuvette is 1 $cm$. The molar absorption coefficient at the given wavelength in $M^{-1}cm^{-1}$, correct to the nearest integer, is ________.
