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Chapter 25: Problem 40

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

Expert verified
The original nonapeptide sequence is Gly-Ala-Phe-Glu-His-Gly-Ala-Leu-Val.

Step by step solution

01

Identify overlapping sequences

To reconstruct the nonapeptide, we first note the overlapping sequences in the given peptides. We have: \[Gly-Ala-Phe, Ala-Leu-Val, Gly-Ala-Leu, Phe-Glu-His, His-Gly-Ala\] Looking at the list, we can observe some overlaps. They are: \[Ala-Phe\] with \[Phe-Glu-His\] and \[His-Gly-Ala\] with \[Gly-Ala-Leu\] and \[Gly-Ala-Phe\]. Overlaps will help to connect the sequences.
02

Combine the peptides

With the identified overlapping sequences, we can start combining the peptides. Start with \[Ala-Phe\] which only appears at the end of \[Gly-Ala-Phe\] and at the beginning of \[Phe-Glu-His\], we get the sequence \[Gly-Ala-Phe-Glu-His\]. Further, to this \[His-Gly-Ala\] can be connected and we get \[Gly-Ala-Phe-Glu-His-Gly-Ala\]. Lastly, \[Gly-Ala-Leu-Val\] is attached at the \[Gly-Ala\] end yielding \[Gly-Ala-Phe-Glu-His-Gly-Ala-Leu-Val\] This sequence has nine residues and does not contradict with any evidence and thus, is the best assembled peptide.
03

Confirm the sequence

Now look back at all the smaller peptides. They all can be found within the assembled nonapeptide body. So this reconstructed sequence fits all the given information. Therefore, the sequence of the original nonapeptide is confirmed to be \[Gly-Ala-Phe-Glu-His-Gly-Ala-Leu-Val\] Remember that the sequence is written from the N-terminus to the C-terminus.

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