5. Protein Techniques

A 660 mg sample of a protein with quaternary structure (MW=132,000 g/mol) was treated with excess 1-fluoro-2,4-dinitrobenzene (FDNB) under slightly alkaline conditions until the reaction was complete. After FDNB treatment, the peptide bonds of the protein were then completely hydrolyzed by heating it with concentrated 6M HCl. The resulting solution was found to contain 5.5 mg of DNP-Val (shown in the figure below):

2,4-Dinitrophenyl derivatives of the α-amino groups of the other amino acids were not detected. Assuming 100% yield for the reaction of FDNB with the protein, determine the number of subunits in this protein.

The peptide Lys-Leu-Leu-Arg-Phe is incubated with FDNB. After exposure to 6M HCl, the solution contains:

After purifying a protein, you react the protein with 1-fluoro-2,4-dinitrobenzene (FDNB or Sanger's reagent) then with 6M HCl. You obtain DNP-Arg and DNP-Asp. Which of the following is an appropriate conclusion of the results?