Asp 102 His 57 -H-N [His] [His+] pH = pK₂ + log (AA [HA] = Ser 195 `N----H-O Identify the ways that His 57 enhances the nucleophilic power of Ser 195. Chymotrypsin is a digestive enzyme with a catalytic optimum between pH 7.8 and 8.0. However, due to the presence of gastri juice, chymotrypsin often functions in an environment of pH 5.5-7.0. The imidazole group of free histidine has a pK₂ of 6.0. Use the Henderson-Hasselbalch equation to determine the ratio of deprotonated to protonated His 57 imidazole moieties at pH 6.1. proton acceptor acid catalyst proton donor base catalyst O Aside from positioning, what do you think is the role of the Asp 102 residue? ○ It allows nucleophilic attack by His 57. [His] ratio. [Hist] It raises the pK₂ of His 57. It protonates His 57 prior to substrate binding. It decreases the
Asp 102 His 57 -H-N [His] [His+] pH = pK₂ + log (AA [HA] = Ser 195 `N----H-O Identify the ways that His 57 enhances the nucleophilic power of Ser 195. Chymotrypsin is a digestive enzyme with a catalytic optimum between pH 7.8 and 8.0. However, due to the presence of gastri juice, chymotrypsin often functions in an environment of pH 5.5-7.0. The imidazole group of free histidine has a pK₂ of 6.0. Use the Henderson-Hasselbalch equation to determine the ratio of deprotonated to protonated His 57 imidazole moieties at pH 6.1. proton acceptor acid catalyst proton donor base catalyst O Aside from positioning, what do you think is the role of the Asp 102 residue? ○ It allows nucleophilic attack by His 57. [His] ratio. [Hist] It raises the pK₂ of His 57. It protonates His 57 prior to substrate binding. It decreases the
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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Proteases are enzymes that cleave peptide bonds using general acid–base catalysis. General acid–base catalysis relies on a proton donor or acceptor other than water. Proteases rely on proton transfer to create strong nucleophiles from active-site amino acid residues.
In the protease chymotrypsin, an active-site serine is a potent nucleophile. A nearby residue, His 57, interacts with serine to increase its reactivity. A schematic of chymotrypsin’s active site illustrates the active site Ser 195 and His 57 R groups. The Asp 102 residue helps position the His 57 residue via hydrogen bonding.
![Asp 102
His 57
·H-N
pH = pka + log
[His]
[His+]
=
Ser 195
Chymotrypsin is a digestive enzyme with a catalytic optimum between pH 7.8 and 8.0. However, due to the presence of gastric
juice, chymotrypsin often functions in an environment of pH 5.5-7.0.
N----H
The imidazole group of free histidine has a pK₁ of 6.0. Use the Henderson-Hasselbalch equation to determine the ratio of
deprotonated to protonated His 57 imidazole moieties at pH 6.1.
[A]
[HA]
Identify the ways that His 57 enhances the nucleophilic
power of Ser 195.
proton acceptor
acid catalyst
proton donor
base catalyst
Aside from positioning, what do you think is the role of
the Asp 102 residue?
It allows nucleophilic attack by His 57.
[His]
It decreases the
[His+]
It raises the pK₁ of His 57.
It protonates His 57 prior to substrate binding.
ratio.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F76ee89b8-722d-4c27-b7b7-9a80c7775531%2F0d3d5c15-d3b8-49bc-8aa4-bfe0b296a287%2F8hpa4ic_processed.png&w=3840&q=75)
Transcribed Image Text:Asp 102
His 57
·H-N
pH = pka + log
[His]
[His+]
=
Ser 195
Chymotrypsin is a digestive enzyme with a catalytic optimum between pH 7.8 and 8.0. However, due to the presence of gastric
juice, chymotrypsin often functions in an environment of pH 5.5-7.0.
N----H
The imidazole group of free histidine has a pK₁ of 6.0. Use the Henderson-Hasselbalch equation to determine the ratio of
deprotonated to protonated His 57 imidazole moieties at pH 6.1.
[A]
[HA]
Identify the ways that His 57 enhances the nucleophilic
power of Ser 195.
proton acceptor
acid catalyst
proton donor
base catalyst
Aside from positioning, what do you think is the role of
the Asp 102 residue?
It allows nucleophilic attack by His 57.
[His]
It decreases the
[His+]
It raises the pK₁ of His 57.
It protonates His 57 prior to substrate binding.
ratio.
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