An oligomeric protein has a molecular weight of 153000. A 960 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 12 mg of the compound shown below, and no other 2,4-dinitrophenyl derivatives of the alpha-amino groups of other amino acids could be found.

How many polypeptide chains are in this protein?