Amino acid analysis provided the following amino acid composition for a decapept

Question

Amino acid analysis provided the following amino acid composition for a decapeptide: alaninei, arginine, glutamic acid, lysine, methionine2, histidinei, phenylalaninei, isoleucine Treatment of the decapeptide with carboxypeptidase B yields free lysine. Reaction of the decapeptide with phenylisothiocyanate followed by TFA hydrolysis and HCl treatment of the released residue liberates the PTH derivative of alanine Reaction of the decapeptide with cyanogen bromide yields a dipeptide (A) and two tetrapeptides (B and C) When subjected to electrophoresis at pH -5.00, peptide C moves toward the negative pole and ends up closest to the negative pole, peptide B moves toward the negative pole, and peptide A hardly moves at all. Reaction of the decapeptide with trypsin yields two tripeptides (D and E) and one tetrapeptide (F). When each peptide is reacted with phenylisothiocyanate followed by TFA and acid hydrolysis, these results are obtained: peptide D yields the PTH derivative of alanine; peptide E yields the PTH derivative of methionine; and peptide F yields the PTH derivative of phenylalanine. Tetrapeptide B (from cyanogen bromide cleavage) and tripeptide E (from trypsin cleavage) contain the most Tetrapeptide B (from cyanogen bromide cleavage) and tetrapeptide F (from trypsin cleavage) are the only What is one possible sequence of the entire decapeptide? How many possible sequences are there? (6 pts) hydrophobic amino acid of these eight amino acids according to both the Kyte & Doolittle scale (used by our book) and the Eisenberg and Weiss scale two peptides that absorb UV light of 260 nm.

Explanation / Answer

Carboxypeptidase cleaves the C-terminal residue present in the peptide. In the given case the residue is lysine.

Hence, a C-terminal residue is Lysine.

Edman degradation reaction Phenylisothiocyanate(PTC) reacts with the N-terminal amino acids and yield PTC derivative of that amino acid Edman degradation yield a compound which is PTC derivative of alanine

Cyanogen bromide cleaves at the C-terminal of methionine residue. so the eight residues of octapeptide are methionine and tetrapeptide has two serine.

Peptide A-

Peptide B

Peptide C

Trypsin enzyme cleaves C-terminal side of Arginine and Lysine.

Peptide D- alanine

Peptide E- Methionine

Peptide F- Phenylalanine

Peptide D is the first fragment of the decapeptide.

The most hydrophobic residue is Isoleucine.

So peptide E and B have Isoleucine.

Amino acid Phenylalanine Absorbs the VU length of wavelength 280nm

So peptide F and B have phenylalanine.

Peptide B has Isoleucine, phenylalanine, methionine, arginine/lysine

Phenylalanine

At pH 5 peptide which has basic amino acid will move towards the negative pole.

So peptide C has two basic amino acid.

Peptide B has one basic amino acid

Peptide A has one basic and one acidic amino acid,

Peptide C- Histidine- arginine/lysine

Peptide A- Aspartic acid - Arginine/lysine

Answer is Alanine-Histidine-Lysine-Methionine-Isoleucine-Arginine-Phenylalanine-Methionine-Glutamic acid-lysine

More possible combinations are-

Alanine-Histidine-Arginine-Methionine-Isoleucine-Arginine-Phenylalanine-Methionine-Glutamic acid-lysine

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