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1. Requirements of Active Sites in Enzymes The active site of an enzyme usually consists of a pocket on the enzyme surface lined with amino acid side chains necessary to bind the substrate and catalyze its chemical transformation. Carboxypeptidase, which sequentially removes the carboxyl-terminal amino acid residues from its peptide substrates, consists of a single chain of 307 amino acids. The two essential catalytic groups in the active site are furnished by Arg145 and Glu²7º. (a) If the carboxpeptidase chain were a perfect a-helix, how far apart (in nanometers) would Arg145 and Glu²7º be? Hint: In an a-helix, there is 1.5 Å translation of the backbone per residue (Chapter 3). (b) Explain how it is that these two amino acids, so distantly separated in the sequence, can catalyze a reaction occurring in the space of a few tenths of a nanometer. (c) If only these two catalytic groups are involved in the mechanism of hydrolysis, why is it necessary for the enzyme to contain such a large number of amino acid residues? 270

1. Requirements of Active Sites in Enzymes The active site of an enzyme usually consists of a pocket on the enzyme surface lined with amino acid side chains necessary to bind the substrate and catalyze its chemical transformation. Carboxypeptidase, which sequentially removes the carboxyl-terminal amino acid residues from its peptide substrates, consists of a single chain of 307 amino acids. The two essential catalytic groups in the active site are furnished by Arg145 and Glu²7º. (a) If the carboxpeptidase chain were a perfect a-helix, how far apart (in nanometers) would Arg145 and Glu²7º be? Hint: In an a-helix, there is 1.5 Å translation of the backbone per residue (Chapter 3). (b) Explain how it is that these two amino acids, so distantly separated in the sequence, can catalyze a reaction occurring in the space of a few tenths of a nanometer. (c) If only these two catalytic groups are involved in the mechanism of hydrolysis, why is it necessary for the enzyme to contain such a large number of amino acid residues? 270

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
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**1. Requirements of Active Sites in Enzymes** The active site of an enzyme usually consists of a pocket on the enzyme surface lined with amino acid side chains necessary to bind the substrate and catalyze its chemical transformation. Carboxypeptidase, which sequentially removes the carboxyl-terminal amino acid residues from its peptide substrates, consists of a single chain of 307 amino acids. The two essential catalytic groups in the active site are furnished by Arg¹⁴⁵ and Glu²⁷⁰. (a) If the carboxypeptidase chain were a perfect α-helix, how far apart (in nanometers) would Arg¹⁴⁵ and Glu²⁷⁰ be? *Hint: In an α-helix, there is 1.5 Å translation of the backbone per residue (Chapter 3).* (b) Explain how it is that these two amino acids, so distantly separated in the sequence, can catalyze a reaction occurring in the space of a few tenths of a nanometer. (c) If only these two catalytic groups are involved in the mechanism of hydrolysis, why is it necessary for the enzyme to contain such a large number of amino acid residues?
Transcribed Image Text:**1. Requirements of Active Sites in Enzymes** The active site of an enzyme usually consists of a pocket on the enzyme surface lined with amino acid side chains necessary to bind the substrate and catalyze its chemical transformation. Carboxypeptidase, which sequentially removes the carboxyl-terminal amino acid residues from its peptide substrates, consists of a single chain of 307 amino acids. The two essential catalytic groups in the active site are furnished by Arg¹⁴⁵ and Glu²⁷⁰. (a) If the carboxypeptidase chain were a perfect α-helix, how far apart (in nanometers) would Arg¹⁴⁵ and Glu²⁷⁰ be? *Hint: In an α-helix, there is 1.5 Å translation of the backbone per residue (Chapter 3).* (b) Explain how it is that these two amino acids, so distantly separated in the sequence, can catalyze a reaction occurring in the space of a few tenths of a nanometer. (c) If only these two catalytic groups are involved in the mechanism of hydrolysis, why is it necessary for the enzyme to contain such a large number of amino acid residues?
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