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

There are 4 tryptophans in the protein.

Step-by-step explanation:

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

Concentration of protein solution = 1.0 micromolar =
`1.0* 10^(-6) Molar`

Molar absorptivity of a protein solution :
`\epsilon`

`\epsilon = \epsilon _(tyro)+\epsilon _(tryp)`

`=1* 2000 M^(-1)cm^(-1)+x* 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 * l* c` ( Beer-Lambert's law)

`0.024=(1* 2000 M^(-1)cm^(-1)+x* 5500 M^(-1)cm^(-1))* 1 cm* 1.0* 10^(-6) M`

Solving for x :

x = 4

There are 4 tryptophans in the protein.