Mapdob Lehninger Principles of Biochemistry Nelson I Cax MHE/Freeman by Sepling
ID: 187416 • Letter: M
Question
Mapdob Lehninger Principles of Biochemistry Nelson I Cax MHE/Freeman by Sepling Learning DNP-Val (a sample (6.10 x102 mg) of an oligomeric protein of M 121,000 was NOz COOH 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 HCI. The hydrolysate was found to contain 5.71 mg of DNP-Val (shown at the right). 2,4- Dinitrophenyl derivatives of the -amino groups of other amino acids could not be found O2N H3C Calculate the number of polypeptide chains in this protein. Give the answer as a whole number Number A second oligomeric protein of Mr 230,000 was shown by a similar endgroup analysis to consist of five polypeptide chains. SDS polyacrylamide gel electrophoresis in the presence of a reducing agent shows three bands: (M 30,000), (M 40,000) and (M 60,000, indicating three distinct polypeptides. SDS electrophoresis without reducing agent also yields three bands, with Mr of 30,000, 40,000, and 120,000 Which of the following oligomeric structures is consistent with this data?Explanation / Answer
a) By comparing the number of moles of the derivative to the number of moles of protein gives the number of polypeptide chains. This is due to fact that only one kind of 2,4-dinitrophenyl (DNP) amino acid derivative is found (signify that all the polypeptide chains have the same amino-terminal residue).
The amount of protein = (0.610 g)/(121,000 g/mol) = 5 x 10-6mol.
The amount of derivatives =(0.00571 g)/(283 g/mol) = 2 x 10-5 mol.
Therefore, no of polypeptide chain = (2 x 10-5 ) /(5 x 10-6) = 4polypeptide chain
b) Molecular weight of oligomeric protein is given 230,000. the end group analysis is showing that protein is made of 5 polypeptide chain.
Now, SDS electrophoresis in reducing state is showing three bands "a" (MW 30,000) "b" (MW 40,000) and "y" (MW 60,000)
the sum of MW of all three chain is 130,000 which is 100,000 Da less than the protein size suggest chain should be "ab2y2 ".
Non reducing SDS gel is also supporting the structure ab2y2, as the sum of MW of all three chain, in this case, is 190,000Da which is 40,000Da less than the molecular weight of Protein.
Hence, option 1 is the correct answer