Question

Determine the sequence of the following pentapeptide using the following laboratory results

Asp, Arg, Gln, Ala, Tyr

Edman Degradation gives Gln

Carboxypeptidase gives Ala

Trypsin gives Ala by itself

Chymotrypsin gives a dipeptide with Gln

Answer 1

Edman reagent reacts with the amino acid present at the N-terminal and gives its derivate.

Carboxypeptidase cleaves the amino acid present that C-terminal.

Trypsin cleaves the C-terminal of arginine and lysine.

Chymotrypsin cleaves the C-terminal of aromatic amino acids.

From the given data Gln is the amino acid present at the N-terminal and Ala at the C-terminal.

Given that digestion by trypsin gives Ala by itself. It means that Arginine is present adjacent to alanine so that alanine is found after digestion by trypsin.

So last two amino acids are Arg-Ala.

Given that digestion by Chymotrypsin gives a dipeptide that has Gln. It means that tyrosine is present adjacent to Gln.

So the sequence of the first two amino acids are Gln- Tye

From the first two and last amino acid, we can find that the third amino acid is Asp.

So the sequence of the peptide is Gln- Tyr - Asp -Arg- Ala.

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