Question

The molar absorptivity of a tyrosine residue at 280 nm is 2000 M-1cm-1, while for tryptophan it is 5500 M-1cm-1. A protein has been isolated that is known to contain one tyrosine residue and an unknown number of tryptophans. A 1.0 micromolar solution of this protein is placed in a 1.0 cm cuvette and the absorbance at 280 nm is measured as 0.024. How many tryptophans are in the protein

Answer 1

Answer:

There are 4 tryptophans in the protein.

Explanation:

According to question,  protein contains one tyrosine residue and say x number of tryptophans.

Concentration of protein solution = 1.0 micromolar = $1.0\times 10^{-6} Molar$

Molar absorptivity of a protein solution : $\epsilon$

$\epsilon = \epsilon _{tyro}+\epsilon _{tryp}$

$=1\times 2000 M^{-1}cm^{-1}+x\times 5500 M^{-1}cm^{-1}$

Length of the cuvette = l = 1.0 cm

Absorbance of protein solution at 280 nm = A = 0.024

$A=\epsilon \times l\times c$ ( Beer-Lambert's law)

$0.024=(1\times 2000 M^{-1}cm^{-1}+x\times 5500 M^{-1}cm^{-1})\times 1 cm\times 1.0\times 10^{-6} M$

Solving for x :

x = 4

There are 4 tryptophans in the protein.