Analysis of a nonapeptide, Compound N, gave the following amino acid composition

Question

Analysis of a nonapeptide, Compound N, gave the following amino acid composition: Ala, Arg, Asp, Gly_2, Gin, Leu, Val_2 Treatment of Compound N with the Edman reagent led to an octapeptide, Compound O, with the following amino acid composition: Ala, Arg, Asp, Gly_2, Gin, Val_2 Treatment of both Compound N and Compound O with the enzyme DPAP gave the following mixtures of peptides: N Arg middot Gly, Gin middot Ala, Leu middot Val, Val middot Asp, Gly O Ala middot Gly, Gly middot Val, Asp middot Gin, Val middot Arg DPAP cleaves a peptide after every second residue from the amino terminus. Determine the amino acid sequence of Compound N.

Explanation / Answer

In Edman degradation the N-terminal amino acid is labelled and cleaved without disturbing the adjacent peptide bond.When compound N (nonapeptide) is treated with Edman reagent it leads to the formation of an octapepetide (componud O) in which Leucine amino acid is absent. So, which means Leu present at N-terminal of compond N.

DPAP cuts second residue from N-terminal. So the amino acid sequence of compound N is;

N- Leu-Val-Asp-Gln-Ala-GlyVal-Arg-Gly- C Terminal.

Leu present at N- terminal ans Gly at C- terminal

When N compound (9 amono acid long) is digested with DPAP which cuts at two amono acid from N- terminal only Gly is the only single amino acid left in nonapepite that mens Gly is present at C-terminal of compound N

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