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4. A hexapeptide has the amino acid composition (Arg, Gly, Met, Trp) The following observations are made: 1) Cyanogen bromide does not cleave the hexapeptide. 2) Trypsin cleaves the hexapeptide into a free Met and a pentapeptide (composed of Arg, Gly, and Trp). 3) Chymotrypsin cleaves the hexapeptide into a free Trp and a pentapeptide (composed of Arg, Gly, and Met). Answer the following questions: a) What is the sequence of the hexapeptide? b) What is the charge of the hexapeptide at pH = 7? c) Suggest a method for separating the products produced by chymotrypsin treatment.

4. A hexapeptide has the amino acid composition (Arg, Gly, Met, Trp) The following observations are made: 1) Cyanogen bromide does not cleave the hexapeptide. 2) Trypsin cleaves the hexapeptide into a free Met and a pentapeptide (composed of Arg, Gly, and Trp). 3) Chymotrypsin cleaves the hexapeptide into a free Trp and a pentapeptide (composed of Arg, Gly, and Met). Answer the following questions: a) What is the sequence of the hexapeptide? b) What is the charge of the hexapeptide at pH = 7? c) Suggest a method for separating the products produced by chymotrypsin treatment.

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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### Problem 4: Hexapeptide Analysis A hexapeptide has the amino acid composition: - Arg (Arginine) - Gly (Glycine) - Met (Methionine) - Trp (Tryptophan) #### The following observations are made: 1. Cyanogen bromide does not cleave the hexapeptide. 2. Trypsin cleaves the hexapeptide into a free Met and a pentapeptide (composed of Arg, Gly, and Trp). 3. Chymotrypsin cleaves the hexapeptide into a free Trp and a pentapeptide (composed of Arg, Gly, and Met). #### Answer the following questions: a) **What is the sequence of the hexapeptide?** b) **What is the charge of the hexapeptide at pH = 7?** c) **Suggest a method for separating the products produced by chymotrypsin treatment.** #### Detailed Explanation: **1. Cyanogen Bromide:** - Cyanogen bromide is a reagent that specifically cleaves at methionine residues. The observation that it does not cleave the hexapeptide suggests that there are no methionine residues internally placed in positions where cleavage would result in measurable fragments. **2. Trypsin:** - Trypsin cleaves at the carboxyl side of lysine and arginine residues unless they are modified. If trypsin cleaves the hexapeptide into a free methionine and a pentapeptide composed of Arg, Gly, and Trp, methionine must be at the terminal position of the hexapeptide. **3. Chymotrypsin:** - Chymotrypsin cleaves at the carboxyl side of aromatic amino acids (such as tryptophan, phenylalanine, and tyrosine). The observation indicates that tryptophan is at a terminal position. **Conclusions for the hexapeptide sequence:** - From the observations, combining the cleavage patterns of trypsin and chymotrypsin, we infer: - Trypsin cleavage indicates Met is at one terminal. - Chymotrypsin cleavage implies Trp is at another terminal. - The presence of Arg, Gly, and one more amino acid in the central sequence suggests: The hexapeptide can be arranged as Met-Arg-Gly-Trp-M
Transcribed Image Text:### Problem 4: Hexapeptide Analysis A hexapeptide has the amino acid composition: - Arg (Arginine) - Gly (Glycine) - Met (Methionine) - Trp (Tryptophan) #### The following observations are made: 1. Cyanogen bromide does not cleave the hexapeptide. 2. Trypsin cleaves the hexapeptide into a free Met and a pentapeptide (composed of Arg, Gly, and Trp). 3. Chymotrypsin cleaves the hexapeptide into a free Trp and a pentapeptide (composed of Arg, Gly, and Met). #### Answer the following questions: a) **What is the sequence of the hexapeptide?** b) **What is the charge of the hexapeptide at pH = 7?** c) **Suggest a method for separating the products produced by chymotrypsin treatment.** #### Detailed Explanation: **1. Cyanogen Bromide:** - Cyanogen bromide is a reagent that specifically cleaves at methionine residues. The observation that it does not cleave the hexapeptide suggests that there are no methionine residues internally placed in positions where cleavage would result in measurable fragments. **2. Trypsin:** - Trypsin cleaves at the carboxyl side of lysine and arginine residues unless they are modified. If trypsin cleaves the hexapeptide into a free methionine and a pentapeptide composed of Arg, Gly, and Trp, methionine must be at the terminal position of the hexapeptide. **3. Chymotrypsin:** - Chymotrypsin cleaves at the carboxyl side of aromatic amino acids (such as tryptophan, phenylalanine, and tyrosine). The observation indicates that tryptophan is at a terminal position. **Conclusions for the hexapeptide sequence:** - From the observations, combining the cleavage patterns of trypsin and chymotrypsin, we infer: - Trypsin cleavage indicates Met is at one terminal. - Chymotrypsin cleavage implies Trp is at another terminal. - The presence of Arg, Gly, and one more amino acid in the central sequence suggests: The hexapeptide can be arranged as Met-Arg-Gly-Trp-M
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