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Chapter 24: Q22P (page 1283)

Show where trypsin and chymotrypsin would cleave the following peptide.

Tyr-Ile-Gln-Arg-Leu-Gly-Phe-Lys-Asn-Trp-Phe-Gly-Ala-Lys-Gly-Gln-Gln.NH2

Short Answer

Expert verified

Trypsin is an enzyme and it breaks down protein into amino acids. It cleaves at the carboxyl side or C-terminal side of the amino acids lysine and arginine.

Cleavage sites of Trypsin

Step by step solution

01

Step-1. Action of trypsin on peptide chain:

Trypsin is an enzyme and it breaks down protein into amino acids. It cleaves at the carboxyl side or C-terminal side of the amino acids lysine and arginine.

Cleavage sites of Trypsin

02

Step-2. Action of chymotrypsin on peptide chain:

Chymotrypsin helps in breaking down protein into smaller units known as amino acids and cleaves at the carboxyl side of aromatic amino acids such as tyrosine, tryptophan, phenylalanine etc.

Cleavage sites of chymotrypsin

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Most popular questions from this chapter

Write the complete structures for the following peptides. Tell whether each peptide is acidic, basic, or neutral.

  1. Methionylthreonine
  2. Threonylmethionine
  3. Arginylaspartyllysine
  4. Glu-Cys-Gln

Show how the following amino acids might be formed in the laboratory by reductive amination of the appropriate α-ketoacid.

Phenylalanine (b) Cysteine (c) Serine (d) Alanine

The Sanger method for N-terminus determination is a less common alternative to the Edman degradation. In the Sanger method, the peptide is treated with the Sanger reagent, 2,4-dinitrofluorobenzene, and then hydrolyzed by reaction with 6 M aqueous HCl. The N-terminal amino acid is recovered as its 2,4-dinitrophenyl derivative and identified.

(a)Propose a mechanism for the reaction of the N terminus of the peptide with 2,4-dinitrofluorobenzene.

(b) Explain why the Edman degradation is usually preferred over the Sanger method.

Complete hydrolysis of an unknown basic decapeptide gives Gly, Ala, Leu, Ile, Phe, Tyr, Glu, Arg, Lys, and Ser. Terminal residue analysis shows that the N terminus is Ala, and the C terminus is Ile. Incubation of the decapeptide with chymotrypsin gives two tripeptides, A and B, and a tetrapeptide, C. Amino acid analysis shows that peptide A contains Gly, Glu, Tyr, and; peptide B contains Ala, Phe, and Lys; and peptide C contains Leu, Ile, Ser, and Arg.Terminal residue analysis gives the following results.

Incubation of the decapeptide with trypsin gives a dipeptide D, a pentapeptide E, and a tripeptide F. Terminal residue analysis of F shows that the N terminus is Ser and the C terminus is Ile. Propose a structure for the decapeptide and for fragments A through F.

Lipoic acid is often found near the active sites of enzymes, usually bound to the peptide by a long, flexible amide linkage with a lysine residue.

(a) Is lipoic acid a mild oxidizing agent or a mild reducing agent? Draw it in both its oxidized and reduced forms.

(b) Show how lipoic acid might react with two Cys residues to form a disulfide bridge.

(c) Give a balanced equation for the hypothetical oxidation or reduction, as you predicted in part (a), of an aldehyde by lipoic acid.

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