An octapeptide was hydrolyzed and the amino acids separated. It was found to hav
ID: 886700 • Letter: A
Question
An octapeptide was hydrolyzed and the amino acids separated. It was found to have the following amino acid composition: Gly (1); Ala (2); Val (1); Lys (2); Met (1); Asp (1). After incubation with FDNB and hydrolysis, 2,4-dinitrophenylalanine was detected. Treatment with cyanogen bromide, which cleaves at M, resulted in two fragments: a pentapeptide containing two K residues and a tripeptide containing V, G, and A. (The residues are not listed in any particular order.) After treatment with trypsin, which cleaves at R and K, there were 3 fragments: two dipeptides and MGAV. What is the sequence of the peptide? Use the one-letter abbreviations for the amino acids, and do not use dashes.
Explanation / Answer
Given about peptide that
Octapeptid = 8 amino acids total
From acid hydrolysis we get
Gly (G) =1 molecule
Ala (A) = 2 molecule
Val (V) = 1 molecule
Lys (K) = 2 molecule
Met (M) =1 molecule
Asp (D) = 1 molecule
After incubation with FDNB and hydrolysis, 2,4-dinitrophenylalanine was detected. 1-Fluoro-2,4-dinitrobenzene reacts with the amino terminal of peptide (Sanger reaction). That means Alanine (A) is terminal amino acid. Positioned 1st from amino terminal.
Treatment with CNBr results in two fragments. Cyanogen bromide (CNBr) hydrolyzes the peptide bond of methionine (M) at carboxyl terminal. That results in
Pentapeptide and tripeptide.
That means Metheonine is at 5th position from amino end of octapeptide.
After the treatment with trypsin:
Trypsin hydrolyzes peptide chains at the carboxyl side of lysine (K) or Arginine (R) results in formation of Two dipeptides and one tetrapeptide MGAV
That shows the position of Lysine (K ) at 2nd and 4th
The overall octapeptide from N to C terminal is
AKDKMGAV
Ala-lys-Asp-lys-met-gly-ala-val