Question

When a nonapeptide (containing nine amino acid residues) isolated from rat brains was hydrolyzed, it gave the following smaller peptides as identifiable products: Gly-Ala-Phe, Ala-Leu-Val, Gly-Ala-Leu, Phe-Glu-His, and His-Gly-Ala. Reconstruct the amino acid sequence in the nonapeptide, giving your reasons. (Remember the convention for writing peptides.)

Short answer

The amino acid sequence in the nonapeptide is Gly-Ala-Phe-Ala-Leu-Val-Phe-Glu-His-Gly-Ala.

Step-by-step solution

Identify Overlapping Peptides

Look at the given sequences and find the ones that overlap. Here, Ala and Gly-Ala are two repeating patterns found in Gly-Ala-Phe, Gly-Ala-Leu and His-Gly-Ala.

Arrange Peptides according to Overlapping Pattern

Based on the repeating patterns, assemble the smaller peptides to determine the sequence, keeping the convention of writing peptides in mind (from left N-Terminus to right C-Terminus). The peptides Gly-Ala, Phe and Ala-Leu-Val overlap to form Gly-Ala-Phe-Ala-Leu-Val.

Identify Remaining Peptides

Following the same method, the peptides Phe-Glu-His and His-Gly-Ala can overlap to form Phe-Glu-His-Gly-Ala.

Finalize Peptide Sequence

Combine the two constructed peptides by identifying the overlapping sequence in both - they both end in Phe and His respectively. Keep in mind the convention of peptide sequence writing. Thus, the final sequence is Gly-Ala-Phe-Ala-Leu-Val-Phe-Glu-His-Gly-Ala.