An octapeptide with the amino acids < Ile, Arg, Met, Phe, Pro, Thr, Tyr, Val > w
ID: 61050 • Letter: A
Question
An octapeptide with the amino acids < Ile, Arg, Met, Phe, Pro, Thr, Tyr, Val > was subjected to digestion reactions A, B and C in order to deduce its amino acid sequence. The following results were obtained. The exact position occupied by each of the amino acids (positions 1-8 in the sequence) will be known when the results are analyzed
A. Digestion with Trypsin yielded a [Thr-Arg] dipeptide and a [hexapeptide] with the remaining amino acids.
Question (A1): Explain the reasoning for the fragmentation pattern
Question (A2): What can you deduce regarding the exact positions occupied by Thr and Arg in the sequence?
B. Cyanogen bromide treatment of the octapeptide also yielded a dipeptide [Phe-Pro] and a hexapeptide.
Question (B1): Explain the reasoning for the above fragmentation pattern (3 points) Question (B2): What can you deduce regarding the exact positions occupied by Phe and Pro in the sequence?
C. Chymotrypsin cleaved the octapeptide into two tetrapeptides, one with and the other
Question (C1): Explain the reasoning for the above pattern Question (C2): What can you deduce regarding the exact positions occupied by Val and Ile in the sequence?
Question (D): What is the sequence of the peptide?
Explanation / Answer
A1. Trypsin enzyme cleaves at the C-termini of Arg residue.
A2. Thy and Arg would be present at the N- terminus of the peptide.
B1. Cyanogen bromide cleaves the peptide at the C- termini of Met residue.
B2. Phe and Pro might be present at the C- terminus of the peptide.
C1. Chymotrypsin cleaves the peptide at the C-termini of Phe, Tyr or Trp, but will not cleave if the next residue is Pro.
C2. Val and Ile residues are present in the middle of the polypeptide.
D. The peptide sequence might be:
Thr-Arg-Val-Tyr-Ile-Met-Phe-Pro