(d) A heptapeptide was found to have an amino acid composition of Asp, Leu, Lys, Met, Phe and Tyr. Trypsin has no effect on the heptapeptide. One cycle of Edman degradation renders: CH2 NH Chymotrypsin treatment yields a dipeptide and a tetrapeptide, as well as a free amino acid. The tetrapeptide is known to contain Leu, Lys, and Met. Cyanogen bromide treatment generates a dipeptide, a tetrapeptide, and free Lys. Determine the amino acid sequence of the heptapeptide. Show how you obtain your answer.

(d) A heptapeptide was found to have an amino acid composition of Asp, Leu, Lys, Met, Phe and Tyr. Trypsin has no effect on the heptapeptide. One cycle of Edman degradation renders: CH2 NH Chymotrypsin treatment yields a dipeptide and a tetrapeptide, as well as a free amino acid. The tetrapeptide is known to contain Leu, Lys, and Met. Cyanogen bromide treatment generates a dipeptide, a tetrapeptide, and free Lys. Determine the amino acid sequence of the heptapeptide. Show how you obtain your answer.

Organic And Biological Chemistry

7th Edition

ISBN:9781305081079

Author:STOKER, H. Stephen (howard Stephen)

Publisher:STOKER, H. Stephen (howard Stephen)

Chapter9: Proteins

Section: Chapter Questions

Problem 9.58EP

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Oxytocin, a nonapeptide hormone secreted by the pituitary gland, functions by stimulating uterine contraction and lactation during childbirth. Its sequence was determined from the following evidence: 1. Oxytocin is a cyclic compound containing a disulfide bridge between two cysteine residues. 2. When the disulfide bridge is reduced, oxytocin has the constitution Asn, Cys2, Gln, Gly, Ile, Leu, Pro, Tyr. 3. Partial hydrolysis of reduced oxytocin yields seven fragments: Asp-Cys, Ile-Glu, Cys-Tyr, Leu-Gly, Tyr-Ile-Glu, Glu-Asp-Cys, and Cys-Pro-Leu. 4. Gly is the C-terminal group. 5. Both Glu and Asp are present as their side-chain amides (Gln and Asn) rather than as free side-chain acids. What is the amino acid sequence of reduced oxytocin? What is the structure of oxytocin itself?
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.
Draw the structure of the N-phenylthiohydantoin formed by initial Edman degradation of each peptide: (a) Ala–Gly–Phe–Phe; (b) Val–Ile–Tyr.
A peptide has the following amino acid composition: 2 Met, 2 Phe, 2 Glu, 1 Arg, 1 Lys, 1 Val, 1 Leu, 1 Gly, 1 Ser Reaction of the intact peptide with dansyl chloride followed by acid hydrolysis creates a derivative of Met. A specific cleavage of the intact peptide produces fragments with the following sequences: Fragment A: Glu-Gly-Lys-Phe Fragment B: Met-Ser-Leu-Arg Fragment C: Met-Val-Glu-Phe What information do this result give about the sequence of the peptide? Explain how you arrived on your answer. a) The sequence is: Met-Val-Glu-Phe-Glu-Gly-Lys-Phe-Met-Ser-Leu-Arg b) The sequence is: Met-Ser-Leu-Arg-Met-Val-Glu-Phe-Glu-Gly-Lys-Phe c) The sequence is: Met-Val-Glu-Phe-Met-Ser-Leu-Arg-Glu-Gly-Lys-Phe d) The sequence is: Met-Ser-Leu-Arg-Glu-Gly-Lys-Phe-Met Val-Glu-Phe
Deduce the sequence of a pentapeptide that contains the amino acids Ala, Glu, Gly, Ser, and Tyr, from the following experimental data. Edman degradation cleaves Gly from the pentapeptide, and carboxypeptidase forms Ala and a tetrapeptide. Treatment of the pentapeptide with chymotrypsin forms a dipeptide and a tripeptide. Partial hydrolysis forms Gly, Ser, and the tripeptide Tyr–Glu–Ala.
There is a hexapeptide, and its primary structure is written down according to the following experimental results, and the analysis process is briefly written down: (1) DNP-Ala was obtained by DNFB reaction; (2) DNP-Ile was obtained by reaction with DNFB after hydrazine hydrolysis; (3) Two tripeptides were obtained by reaction with cyanogen bromide, then DNP-Leu and DNP-Ala were obtained by reaction with DNFB; (4) Fragments containing 1, 2 and 3 amino acids were obtained by trypsin hydrolysis, and the Sakakuchi reaction of the last two fragments was positive.
2. (a) Describe any two of the secondary structure elements found in peptides. (b) Why do Glycine and Proline destabilise an a-helix secondary structure element? (c) Provide a definition of the term isoelectric point? (d) Using the information given below, calculate the pl of the amino acid citrulline. H₂N pK₂ = 9.23 H₂N. NH COOH pK₂ = 2.27
Cyanogen bromide fragments: SDKARPM, DSKLAM, DEM, DQ Trypsin fragments: LAMSDK, ARPMDQ, DEMDSK What is the sequence of the original peptide? ARPMDQDEMDSKLAMSDK ODEMDSKLAMSDKARPMDQ OLAMSDKDEMDSKARPMDQ DEMDSKARPMDQLAMSDK
19. Where do the following enzymes cleave peptides at? (i.e. what residue) carboxypeptidase trypsin chymotrypsin
(a) Draw a structural formula for the products formed when alanine is treated with the following reagents. (i) (Boc)20, NaOH (ii) CbzCI, NazCO3 (iii) 2-Methylpropene, p-TSOH (b) Enfuvirtide, a 36-amino-acid peptide drug, was manufactured at a multi-tonne per year scale. The manufacture relied on solid phase synthesis with Barlos resin as the solid support. Part of the solid phase synthesis is shown below. Write the structure of the product A and discuss the cleavage mechaniśm of the peptide from the resin. 1. Fmoc-Leu-OH, DIPEA 2. 20% piperidine in DMF 3. Fmoc-Glu('Bu)-OH, HBTU, HOBt 4. 20% piperidine in DMF 5. Fmoc-Leu-OH, HBTU, HOBT 6. 20% piperidine in DMF 7. Fmoc-Leu-OH, HBTU, HOBE 8. 20% piperidine in DMF 9. 10% HOAC in CH2CI2 Barlos resin
What peptides are expected to be produced when a-melanotropin (Problem 2) is cleaved by (a) trypsin, (b) cyanogen bromide, and (c) thermolysin?