Question

Protein X has two tryptophans and one tyrosine, and its molecular weight is

20,000 Da. One molar tryptophan and one molar tyrosine solutions give you Abs280 of

5500 and 1490, respectively (using a one cm path length cuvette). What Abs280 would

you expect for 0.2 mg/ml of protein X solution?​

Answer 1

The absorbance peak will be 0.312

We do this by using the Beer - lambert's law :- A = εCL

• Molar Extinction Coefficient of protein, ε = (Number of Tryptophan residues X 5500) + (Number of Tyrosine residues X 1490)  = 2 x 5500 + 1 x 1490  = 12490
• concentration of protein, C = 0.2 / 20000 M = 0.25 * 10^( -4 )
• path length of cuvette, L = 1 cm

• A = εCL = 12490 * 0.25 * 10^(-4) * 1 = 0.31225 ≈ 0.312