A heptapeptide Ala₂,Glu,Phe,Pro,Tyr,Val gives labeled alanine when heated with DNFB followed by hydrolysis.On partial hydrolysis the unlabeled heptapeptide gives the following: Ala·Glu,Pro·Tyr,Ala·Val,Tyr·Ala,Val·Phe·Pro.
What is the amino acid sequence of the heptapeptide?

Question

Quizplus · Accepted Answer

The presence of labeled alanine indicates that the peptide must have an alanine residue present. Looking at the partial hydrolysis products, we can see that there are Ala·Glu and Tyr·Ala fragments, indicating that the alanine residue is at either end of the peptide. Also, there is a Val·Phe·Pro fragment, indicating that Val and Pro must be consecutive residues in the sequence. From there, we can see that Tyr must be followed by either Ala or Val, and Glu must be either at the beginning or end of the sequence. Putting all of these observations together, we get the sequence: Ala·Val·Phe·Pro·Tyr·Ala·Glu, which matches choice B.

A Heptapeptide Ala2,Glu,Phe,Pro,Tyr,Val Gives Labeled Alanine When Heated with DNFB

A Heptapeptide Ala₂,Glu,Phe,Pro,Tyr,Val Gives Labeled Alanine When Heated with DNFB