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52 2. Glutathione is called γ-glutamylcysteylglycine. Write a formula for glutathione. What is the role of glutathione in the human body? 3. Write formulas of carnosine dipeptides (β-alanylhistidine) and anserine (β-alanyl-N‑methyl-histidine) contained in the muscles of animals and humans. 4. Write formulas for opioid pentapeptides of leu-enkephalin (Tir-Gly-Gly- Phe-Nyle) and met-enkephalin (Tir-Gly-Gly-Phen-Meth). 5. Write the hydrolysis equation for tripeptides: a) Ala-Pro-Gly; b) Ser-Gl- Argh. 6. Write the equation of reaction for determining the amino acid sequence for the tripeptides Tyr-Glu-Ala and Gis-Ser-Cis by the Edman method. Write the formulas of phenylthiohydantoin (FTH)-derivatives of α-amino acids obtained by degradation by the Edman method from these tripeptides. 7. Will the peptides glutathione, vasopressin, oxytocin, carnosine, anserine give a positive reaction with Pb  2+ ions? Explain these processes. 8. Will the peptides Glu-Tir-Ala-Val, Gly-Pro-Fen-Gis, Pro-Liz-Gly-Leigh give a positive reaction with concentrated nitric acid? Explain these processes. 9. What is the result of the pentapeptide Ala-Serg-Gly-Gis-Asp during the ninhydrin and biuret reaction? Why? 10. Why are ninhydrin and biuret reactions universal for all peptides and proteins? Explainthese processes. 11. What electrode do tripeptides Glu-Val-Asp, Asp-Gla-Ala, Lys-Arg-Gis, Ley-Liz-Argh move to at pH = 7.6 in the electric field? Laboratory work. Experiment 1. Biuret reaction to peptide bond. Place 5–6 drops of egg white’s solution in a test tube, add an equal volume of 10% NaOH solution and add 1–2 drops of CuSO 4  solution along the wall. What are you observing? Write a scheme of biuret formation. Experiment 2. Xantoprotein reaction of proteins. Place 10 drops of egg white’s solution into the tube and 2 drops of concentrated nitric acid. Carefully heat the contents of the tube under constant stirring. What color have the solution and sediment? After cooling the tube, carefully add 1–3 drops of a 10% solution of NaOH. How does the color change? Write the reaction’s scheme. Experiment 3. Reaction to the presence of sulfur-containing amino acids (Fole’s reaction). Place 10 drops of egg white solution into the tube and double the volume of 10% NaOH solution. Mix the contents of the tube and