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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

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

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