An oligomeric protein has a molecular weight of 4.80 × 105. A 540 mg sample was

Question

An oligomeric protein has a molecular weight of 4.80 × 105. A 540 mg sample was treated with an excess of 1-fluoro-2,4-dinitrobenzene (Sanger's reagent) until the reaction was complete. Next the peptide bonds were hydrolyzed by heating with concentrated HCl. The product of the complete hydrolysis contained 1.1 mg of the compound shown below, and no other 2,4-dinitrophenyl derivatives of the ?-amino groups of other amino acids could be found.

An oligomeric protein has a molecular weight of 4.80 x105. A 540 mg sample was treated with an excess of 1-fluoro-2,4-dinitrobenzene (Sanger's reagent) until the reaction was complete. Next the peptide bonds were hydrolyzed by heating with concentrated HCI. The product of the complete hydrolysis contained 1.1 mg of the compound shown below, and no other 2,4-dinitrophenyl derivatives of the a- amino groups of other amino acids could be found. NO2 How many polypeptide chains are in this protein? (Enter your answer as a whole number) NH-C-COOH CH2 CH2 Number 2 CH3

Explanation / Answer

molar mass of protein = 480000 gm/mol.

sample taken = 540 mg = 0.54 gm

molar mass = 0.54/480000 = 1.12 x 10-6

and Sanger’s reagent reacts with the N-terminal residue

1.1 mg obtain = 0.0011 gm

molar mass of derivative = 0.0011/317 = 3.47 x 10-6

molar mass of derivative / molar mass of protein = 3.47 x 10-6 / 1.12 x 10-6 = 3 (approx)

so the protein is made up of 3 peptide chain.

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