Question

Question 13 of 19 > Suppose Kara has isolated a peptide and must determine the amino acid sequence. After one cycle of Edman degradation on a sample of the peptide, she produces a phenylthiohydantoin (PTH) derivative, OH Treatment with cyanogen bromide on another sample of her peptide gives her the fragments • Lys-Pro-Ala-Met, • Pro-Asp. • Leu-Ile-Cys-Trp-Met, and • Thr-Arg.Met. She also digested a sample of her peptide with the enzyme chymotrpsin. One of the fragments produced after treatment with chymotrypsin is Met-Pro-Asp. Determine the amino acid sequence using the results of the various peptide treatments. Place the fragments in order

Answer 1

Cyanogen bromide cleaves at C- terminal of methionine residues. Thus the second peptide must be in the last of the sequence because it does not have any methionine residue. Chymotrypsin cleaves C- terminal of aromatic amino acid that are W, Y, and F. So the correct order of amino acids/ peptides in this protein will be-

TRM-KPAM-LICTM-PE

Where all single letter codes are taken for the peptide here. Chymotrypsin will cleave at carboxy-terminus of tryptophan and a fragment of MPE leaves behind.