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Chapter 27: Problem 8
What amino acid does each abbreviation stand for? (a) Phe (b) Ser (c) Asp (d) Gln (e) His (f) Gly (g) Tyr
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As discussed in Chemical Connections: "Vitamin \(\mathrm{K}\), Blood Clotting, and Basicity" in Section \(26.6 \mathrm{D}\), vitamin \(\mathrm{K}\) participates in carboxylation of glutamic acid residues of the blood-clotting protein prothrombin. (a) Write a structural formula for \(\gamma\)-carboxyglutamic acid. (b) Account for the fact that the presence of \(\gamma\)-carboxyglutamic acid escaped detection for many years; on routine amino acid analyses, only glutamic acid was detected.
A decapeptide has the following amino acid composition. $$ \mathrm{Ala}_{2} \text {, Arg, Cys, Glu, Gly, Leu, Lys, Phe, Val } $$ Partial hydrolysis yields the following tripeptides. $$ \text { Cys-Glu-Leu + Gly-Arg-Cys + Leu-Ala-Ala + Lys-Val-Phe + Val-Phe-Gly } $$ One round of Edman degradation yields a lysine phenylthiohydantoin. From this information, deduce the primary structure of this decapeptide.
A chemically modified guanidino group is present in cimetidine (Tagamet), a widely prescribed drug for the control of gastric acidity and peptic ulcers. Cimetidine reduces gastric acid secretion by inhibiting the interaction of histamine with gastric \(\mathrm{H}_{2}\) receptors. In the development of this drug, a cyano group was added to the substituted guanidino group to alter its basicity. Do you expect this modified guanidino group to be more basic or less basic than the guanidino group of arginine? Explain.
Distinguish between intermolecular and intramolecular hydrogen bonding between the backbone groups on polypeptide chains. In what type of secondary structure do you find intermolecular hydrogen bonds? In what type do you find intramolecular hydrogen bonding?
2,4-Dinitrofluorobenzene, very often known as Sanger's reagent after the English chemist Frederick Sanger who popularized its use, reacts selectively with the \(N\)-terminal amino group of a polypeptide chain. Sanger was awarded the 1958 Nobel Prize for chemistry for his work in determining the primary structure of bovine insulin. One of the few persons to be awarded two Nobel Prizes, he also shared the 1980 award in chemistry with American chemists, Paul Berg and Walter Gilbert, for the development of chemical and biological analyses of DNA. Following reaction with 2,4-dinitrofluorobenzene, all amide bonds of the polypeptide chain are hydrolyzed, and the amino acid labeled with a 2,4-dinitrophenyl group is separated by either paper or column chromatography and identified. (a) Write a structural formula for the product formed by treatment of the \(N\)-terminal amino group with Sanger's reagent and propose a mechanism for its formation. (b) When bovine insulin is treated with Sanger's reagent followed by hydrolysis of all peptide bonds, two labeled amino acids are detected: glycine and phenylalanine. What conclusions can be drawn from this information about the primary structure of bovine insulin? (c) Compare and contrast the structural information that can be obtained from use of Sanger's reagent with that from use of the Edman degradation.
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