Tetrapeptide A is completely hydrolysed under acidic conditions to yield alanine, aspartic acid, isoleucine and valine. On neutralisation of the hydrolysate, an odour of ammonia is detected. The reaction of the tetrapeptide with phenylisothiocyanate, followed by mild hydrolysis yields no phenylthiohydantoin derivative. Incubation of A with carboxypeptidase A has no effect either. Explain

Tetrapeptide A is completely hydrolysed under acidic conditions to yield alanine, aspartic acid, isoleucine and valine. On neutralisation of the hydrolysate, an odour of ammonia is detected. The reaction of the tetrapeptide with phenylisothiocyanate, followed by mild hydrolysis yields no phenylthiohydantoin derivative. Incubation of A with carboxypeptidase A has no effect either. Explain

Organic Chemistry

8th Edition

ISBN:9781305580350

Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Publisher:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote

Chapter27: Amino Acids And Proteins

Section: Chapter Questions

Problem 27.19P

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Aspartame (Nutrasweet®) is a remarkably sweet-tasting dipeptide ester. Complete hydrolysis of aspartame gives phenylalanine, aspartic acid, and methanol. Mild incubation with carboxypeptidase has no effect on aspartame. Treatment ofaspartame with phenyl isothiocyanate, followed by mild hydrolysis, gives the phenylthiohydantoin of aspartic acid.Propose a structure for aspartame.
An octapeptide contains the following amino acids: Arg, Glu, His, Ile, Leu, Phe, Tyr, and Val. Carboxypeptidase treatment of the octapeptide forms Phe and a heptapeptide. Treatment of the octapeptide with chymotrypsin forms two tetrapeptides, A and B. Treatment of A with trypsin yields two dipeptides, C and D. Edman degradation cleaves the following amino acids from each peptide: Glu (octapeptide), Glu (A), Ile (B), Glu (C), and Val (D). Partial hydrolysis of tetrapeptide B forms Ile–Leu in addition to other products. Deduce the structure of the octapeptide and fragments A–D.
The peptide Proline-Serine-Alanine-Phenylalanine-Glutamine is present at pH 7. Draw the peptide and include stereochemistry.
Although tryptophan contains a heterocyclic amine, it is considered a neutral aminoacid. Explain why the indole nitrogen of tryptophan is more weakly basic than one ofthe imidazole nitrogens of histidine.
A tripeptide on hydrolysis produced glycine, alanine and leucine. The structures of these amino acids are shown below. On reaction with Edman’s reagent, leucine was released as the phenylhydantoin. Treatment of the tripeptide with carboxypeptidase gave glycine. Draw the structure of the tripeptide.
Deduce the sequence of a heptapeptide that contains the amino acids Ala, Arg, Glu, Gly, Leu, Phe, and Ser, from the following experimental data. Edman degradation cleaves Leu from the heptapeptide, and carboxypeptidase forms Glu and a hexapeptide. Treatment of the heptapeptide with chymotrypsin forms a hexapeptide and a single amino acid. Treatment of the heptapeptide with trypsin forms a pentapeptide and a dipeptide. Partial hydrolysis forms Glu, Leu, Phe, and the tripeptides Gly-Ala-Ser and Ala-Ser-Arg.
Deduce the sequence of a heptapeptide that contains the amino acids Ala, Arg, Glu, Gly, Leu, Phe, and Ser, from the following experimental data. Edman degradation cleaves Leu from the heptapeptide, and carboxypeptidase forms Glu and a hexapeptide. Treatment of the heptapeptide with chymotrypsin forms a hexapeptide and a single amino acid. Treatment of the heptapeptide with trypsin forms a pentapeptide and a dipeptide. Partial hydrolysis forms Glu, Leu, Phe, and the tripeptides Gly–Ala–Ser and Ala–Ser–Arg.
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The anti-obesity drug orlistat works by irreversibly inhibiting pancreatic lipase, an enzyme responsible for the hydrolysis of triacylglycerols in the intestines, so they are excreted without metabolism. Inhibition occurs by reaction of orlistat with a serine residue of the enzyme, forming a covalently bound, inactive enzyme product. Draw the structure of the product formed during inhibition.
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