Two peptide samples of the same sequence were degraded using two different metho

Question

Two peptide samples of the same sequence were degraded using two different methods. In first method, the peptide sample was completely degraded after four cycles of Edman degradation. In the second method, three floresecent dansylamino acids were generated after treating the sample with dansyl-chloride followerd by treatment with an acid.

a. Explain what does Edman degradation does

b. Explain what the three floresecent dansylamino acids means

c. predict one possible sequence for the peptide using its 3-letter abbreviation

Explanation / Answer

a.

edman degradation method is used for determining the sequences of peptides and proteins from their N-terminus , it was developed by Pehr Edman. this chemical method uses phenylisothiocyanate for sequential removal of amino acid residues from the N terminus of a polypeptide chain.

phenylisothiocyanate reacts with N terminal amino group of polypeptide under mildly alkaline conditions, to form the phenylthiocarbamyl-peptide derivative(PTC- peptide) , the under acidic condition in the presence of anhydrous trifluoroacetic acid, this derivative of the terminal amino acid is cleaved as a thiazolinone derivative. the thiazolinone amino acid is then selectively extracted into an organic solvent and treated with aqueous acid to form the more stable phenylthiohydantoin amino acid derivative that can be identified by using chromatography or electrophoresis.

b.

fluorescent dansyl amino acid means- when dansyl chloride reacts with a free amino group of the N terminal amino acid residue of a peptide in alkaline solution to form a strongly fluorescent derivatives of free amino acids and N terminal amino acid residue of peptides.

this analysis is done by using Sanger's sequencing of protein.

here, reagents 1 fluoro-2,4-dinitrobenzene(FDNB) and dansyl chloride are used for determination of N terminal amino acid residue. FDNB reacts in alkaline solution with the free amino group of N terminal amino acid residue of a peptide to form a characteristic yellow dinitrophenyl derivative. it can be released from the peptide by either acid or enzymatic hydrolysis of the peptide bond and subsequently identified.

c.

Tyr-Phe-Ala

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