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Using CNBr a polypeptide is cleaved into 4 smaller peptides: 1. Asp-Ile-Lys-Gln-

ID: 6809 • Letter: U

Question

Using CNBr a polypeptide is cleaved into 4 smaller peptides:
1. Asp-Ile-Lys-Gln-Met
2. Lys
3. Lys-Phe-Ala-Met
4. Tyr-Arg-Gly-Met

Using a fresh (different) sample of the SAME polypeptide, a different test is performed using Trypsin. Trypsin is known to cleave at the "C" side of basic residues [where Rm-1 = Lys and Arg (Rm does not= Pro)]. After using Trypsin the polypeptide is cleaved into these 4 smaller peptides:
a. Gln-Met-Lys
b. Gly-Met-Asp-Ile-Lys
c. Phe-Ala-Met-Lys
d. Tyr-Arg

What was the original polypeptide and why?

Explanation / Answer

From the data given the original polypeptide sequence is Tyr- Agr- Gly- Met - Asp- Ile- Lys- Gln- Met- Lys- phe- Ala- Met- Lys