Biology Practice Problems Proteins Practice Problems Solution: Amino acid analysis of an oligopeptide seven resid...

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Solution: Amino acid analysis of an oligopeptide seven residures long gave the following amino acids:Asp  Leu  Lys  Met  Phe  TyrThe 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.

Problem

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.

Solution

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.

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