🤓 Based on our data, we think this question is relevant for Professor Barshay's class at UCONN.
Amino acid analysis of an oligopeptide seven residures long gave the following amino acids:
Asp Leu Lys Met Phe Tyr
The following facts were observed:
a. Trypsin treatment had no apparent effect.
b. The phenylthiohydantoin (PTH) derivative by Edman degradation was: (See th figure below)
c. Chymotrypsin treatment resulted in 3 fragments, including a dipeptide and tetrapeptide. The tetrapeptide contained the amino acids Asp, Leu, Met, and Lys (in that order).
d. Cyanogen bromide treatment yielded a dipeptide, tetrapeptide, and free Lys.
What is the amino acid peptide sequence for this heptapeptide? Label N and C termini.
a. Trypsin treatment cleaves the C-side of basic amino acids (AAs). Lys is a basic AA. The apparent lack of effect of Trypsin simply means that there are no AAs to be cleaved in the C-side of lys. Thus, lys is at the C-terminal.
b. The structure of the PTH derivative determines that Phe is the N terminal of the peptide.