A sample (885 mg) of an oligomeric protein of M r 155,000 was treated with an excess of 1‑fluoro‑2,4‑dinitrobenzene (Sanger's reagent) under slightly alkaline conditions until the chemical reaction was complete. The peptide bonds of the protein were then completely hydrolyzed by heating it with concentrated HCl. The hydrolysate was found to contain 4.85 mg of DNP‑Val. 2,4‑Dinitrophenyl derivatives of the α‑amino groups of other amino acids could not be found. Calculate the number of polypeptide chains in this protein. Give the answer as a whole number.

In 1945, Frederick Sanger described its use for determining the N-terminal amino acid in polypeptide chains, in particular insulin.[4] Sanger's initial results suggested that insulin was a smaller molecule than previously estimated (molecular weight 12,000), and that it consisted of four chains (two ending in glycine and two ending in phenylalanine), with the chains cross-linked by disulfide bonds. Sanger continued work on insulin, using dinitrofluorobenzene in combination with other techniques, eventually resulted in the complete sequence of insulin (consisting of only two chains, with a molecular weight of 6,000).[5]

Following Sanger's initial report of the reagent, the dinitrofluorobenzene method was widely adopted for studying proteins, until it was superseded by other reagents for terminal analysis (e. g., dansyl chloride and later aminopeptidases and carboxypeptidases) and other general methods for sequence determination (e. g., Edman degradation).[5]

Dinitrofluorobenzene reacts with the amine group in amino acids to produce dinitrophenyl-amino acids. These DNP-amino acids are moderately stable under acid hydrolysis conditions that break peptide bonds. The DNP-amino acids can then be recovered, and the identity of those amino acids can be discovered through chromatography. More recently, Sanger's reagent has also been used for the rather difficult analysis of distinguishing between the reduced and oxidized forms of glutathione and cysteine in biological systems in conjunction with HPLC. This method is so rugged that it can be performed in such complex matrices as blood or cell lysate.[6][7]

Explanation:

Example: A sample (525 mg) of an oligomeric protein of Mr 117,000 was treated COOH with an excess of1-fluoro-2,4-dinitrobenzene (Sanger's reagent) under slightly alkaline conditions until thechemical reaction was complete. The peptide bonds of the protein were then completelyhydrolyzed by heating it with concentrated HCI. The hydrolysate was found to contain 3.37 mgof DNP-Val (shown at the right), 2,4-Dinitrophenyl derivatives of the α - amino groups of otheramino acids could not be found H3C Calculate the number of polypeptide chains in this protein. Give the answer as a whole number Number A second oligomeric protein of M 230,000 wasshown by a similar endgroup analysis to consist of five polypeptide chains. SDS polyacrylamidegel electrophoresis in the presence of a reducing agent shows three bands: α (M, 30,000), β (M40,000) and γ (M-60,000), indicating three distinct polypeptides. SDS electrophoresis withoutreducing agent also yields three bands, with Mr of 30,000, 40,000, and 120,000 Which of the