As you know, the enolase enzyme of glycolysis utilizes an E1CB mechanism to expel hydroxide as a leaving group, converting 2-PG to PEP. Like other transformations we have studied in this course, enolase has strict stereoelectronic requirements for its substrate. Two possible conformations of the intermediate within the enolase active site are shown below. (Some bond lengths are exaggerated for clarity.) HO H H =0 H OH HO Conformation 1 HO Conformation 2 a) State which of these two conformations is correct, and briefly explain. For full credit, your explanation must cite a specific donor-acceptor orbital interaction and alignment. You do not need to draw any "cartoon" orbitals. b) As shown above, the phosphate group of 2-PG is maintained in an unusual state within the enzyme active site. Briefly explain what is unusual about this phosphate group under physiologic conditions, and what strategic advantage this provides for the reaction. c) PEP, the product of the enolase reaction, is considered a high-energy glycolytic intermediate, and its formation is endergonic (AG>0). In the box below, draw the structure of PEP. (Hint: you do not need to have memorized its structure from lecture! Simply work through the arrows from the appropriate intermediate given above to finish the E1CB reaction.) Do not use any structural abbreviations. PEP Structure d) State two reasons why the formation of this high-energy intermediate is overall advantageous for energy metabolism despite being thermodynamically "uphill."
As you know, the enolase enzyme of glycolysis utilizes an E1CB mechanism to expel hydroxide as a leaving group, converting 2-PG to PEP. Like other transformations we have studied in this course, enolase has strict stereoelectronic requirements for its substrate. Two possible conformations of the intermediate within the enolase active site are shown below. (Some bond lengths are exaggerated for clarity.) HO H H =0 H OH HO Conformation 1 HO Conformation 2 a) State which of these two conformations is correct, and briefly explain. For full credit, your explanation must cite a specific donor-acceptor orbital interaction and alignment. You do not need to draw any "cartoon" orbitals. b) As shown above, the phosphate group of 2-PG is maintained in an unusual state within the enzyme active site. Briefly explain what is unusual about this phosphate group under physiologic conditions, and what strategic advantage this provides for the reaction. c) PEP, the product of the enolase reaction, is considered a high-energy glycolytic intermediate, and its formation is endergonic (AG>0). In the box below, draw the structure of PEP. (Hint: you do not need to have memorized its structure from lecture! Simply work through the arrows from the appropriate intermediate given above to finish the E1CB reaction.) Do not use any structural abbreviations. PEP Structure d) State two reasons why the formation of this high-energy intermediate is overall advantageous for energy metabolism despite being thermodynamically "uphill."
Chapter11: Reactions Of Alkyl Halides: Nucleophilic Substitutions And Eliminations
Section11.SE: Something Extra
Problem 79AP
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Transcribed Image Text:As you know, the enolase enzyme of glycolysis utilizes an E1CB mechanism to expel hydroxide
as a leaving group, converting 2-PG to PEP. Like other transformations we have studied in this course,
enolase has strict stereoelectronic requirements for its substrate. Two possible conformations of the
intermediate within the enolase active site are shown below. (Some bond lengths are exaggerated for
clarity.)
HO
H
H
=0
H
OH
HO
Conformation 1
HO
Conformation 2
a) State which of these two conformations is correct, and briefly explain. For full credit, your explanation
must cite a specific donor-acceptor orbital interaction and alignment. You do not need to draw any
"cartoon" orbitals.
b) As shown above, the phosphate group of 2-PG is maintained in an unusual state within the enzyme
active site. Briefly explain what is unusual about this phosphate group under physiologic conditions,
and what strategic advantage this provides for the reaction.
c) PEP, the product of the enolase reaction, is considered a high-energy glycolytic intermediate, and
its formation is endergonic (AG>0). In the box below, draw the structure of PEP. (Hint: you do not need
to have memorized its structure from lecture! Simply work through the arrows from the appropriate
intermediate given above to finish the E1CB reaction.) Do not use any structural abbreviations.
PEP Structure
d) State two reasons why the formation of this high-energy intermediate is overall advantageous for
energy metabolism despite being thermodynamically "uphill."
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