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10. Chymotrypsin is a serine protease enzyme. The Km for the reaction of chymotrypsin with N-acetylvaline ethyl ester is 8.8*102, and the Km for the reaction of chymotrypsin with N- acetyltyrosine ethyl ester is 6.6*10“ M. catalytic triad Ser 195 His 57 Gly 193 N-H HO R-N- Ca N-H O-C Asp 102 N-acetyl valine N-acetyl tyrosine Chymotrypsin Active Site a. What is the nucleophile here and how is it activated? b. Which substrate has an apparent higher affinity for the enzyme. c. Propose a reason for the difference in affinity based on the shape of each of the substrates (see active site figure, cleaves on the C-side of aromatic residues).

10. Chymotrypsin is a serine protease enzyme. The Km for the reaction of chymotrypsin with N-acetylvaline ethyl ester is 8.8*102, and the Km for the reaction of chymotrypsin with N- acetyltyrosine ethyl ester is 6.6*10“ M. catalytic triad Ser 195 His 57 Gly 193 N-H HO R-N- Ca N-H O-C Asp 102 N-acetyl valine N-acetyl tyrosine Chymotrypsin Active Site a. What is the nucleophile here and how is it activated? b. Which substrate has an apparent higher affinity for the enzyme. c. Propose a reason for the difference in affinity based on the shape of each of the substrates (see active site figure, cleaves on the C-side of aromatic residues).

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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**Chymotrypsin and Substrate Affinity** **10. Chymotrypsin is a serine protease enzyme.** The \(K_m\) for the reaction of chymotrypsin with N-acetylvaline ethyl ester is \(8.8*10^{-2}\), and the \(K_m\) for the reaction of chymotrypsin with N-acetyltyrosine ethyl ester is \(6.6*10^{-4}\) M. **Chemical Structures:** - **N-acetyl valine:** Displays a chemical structure involving an acetyl group with valine. - **N-acetyl tyrosine:** Contains an aromatic ring in the acetyl tyrosine structure. **Diagram Explanation:** The **Chymotrypsin Active Site** diagram illustrates the catalytic triad consisting of Ser 195, His 57, and Asp 102. The substrate fits into the enzyme's active site, where the nucleophilic attack occurs, facilitating the proteolytic cleavage. **Questions:** a. **What is the nucleophile here and how is it activated?** b. **Which substrate has an apparent higher affinity for the enzyme?** c. **Propose a reason for the difference in affinity based on the shape of each of the substrates (see active site figure, cleaves on the C-side of aromatic residues).** **Answer Guide:** a. **Nucleophile and Activation:** The nucleophile in chymotrypsin is the serine residue (Ser 195) in the active site. It is activated through a charge relay system involving the catalytic triad, where His 57 and Asp 102 facilitate the deprotonation of the serine hydroxyl group to enhance its nucleophilicity. b. **Higher Affinity Substrate:** N-acetyltyrosine ethyl ester has a higher affinity for the enzyme, indicated by its lower \(K_m\) value (\(6.6*10^{-4}\) M compared to \(8.8*10^{-2}\)). c. **Reason for Affinity Difference:** The higher affinity of N-acetyltyrosine is likely due to the presence of an aromatic ring, which better fits the chymotrypsin active site that cleaves on the C-side of aromatic residues, enhancing interaction and specificity. The shape and structure of this substrate allow for
Transcribed Image Text:**Chymotrypsin and Substrate Affinity** **10. Chymotrypsin is a serine protease enzyme.** The \(K_m\) for the reaction of chymotrypsin with N-acetylvaline ethyl ester is \(8.8*10^{-2}\), and the \(K_m\) for the reaction of chymotrypsin with N-acetyltyrosine ethyl ester is \(6.6*10^{-4}\) M. **Chemical Structures:** - **N-acetyl valine:** Displays a chemical structure involving an acetyl group with valine. - **N-acetyl tyrosine:** Contains an aromatic ring in the acetyl tyrosine structure. **Diagram Explanation:** The **Chymotrypsin Active Site** diagram illustrates the catalytic triad consisting of Ser 195, His 57, and Asp 102. The substrate fits into the enzyme's active site, where the nucleophilic attack occurs, facilitating the proteolytic cleavage. **Questions:** a. **What is the nucleophile here and how is it activated?** b. **Which substrate has an apparent higher affinity for the enzyme?** c. **Propose a reason for the difference in affinity based on the shape of each of the substrates (see active site figure, cleaves on the C-side of aromatic residues).** **Answer Guide:** a. **Nucleophile and Activation:** The nucleophile in chymotrypsin is the serine residue (Ser 195) in the active site. It is activated through a charge relay system involving the catalytic triad, where His 57 and Asp 102 facilitate the deprotonation of the serine hydroxyl group to enhance its nucleophilicity. b. **Higher Affinity Substrate:** N-acetyltyrosine ethyl ester has a higher affinity for the enzyme, indicated by its lower \(K_m\) value (\(6.6*10^{-4}\) M compared to \(8.8*10^{-2}\)). c. **Reason for Affinity Difference:** The higher affinity of N-acetyltyrosine is likely due to the presence of an aromatic ring, which better fits the chymotrypsin active site that cleaves on the C-side of aromatic residues, enhancing interaction and specificity. The shape and structure of this substrate allow for
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