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Questions and Answers
What is the effect of inhibiting isocitrate dehydrogenase?
What is the effect of inhibiting isocitrate dehydrogenase?
The Aconitase reaction is reversible.
The Aconitase reaction is reversible.
True
What regulates the flow of α-ketoglutarate at the branch point?
What regulates the flow of α-ketoglutarate at the branch point?
Succinyl-CoA
Citrate synthase is also inhibited by ____________________.
Citrate synthase is also inhibited by ____________________.
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Match the enzymes with their regulatory mechanisms:
Match the enzymes with their regulatory mechanisms:
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What is the result of accumulated citrate leaving the mitochondria?
What is the result of accumulated citrate leaving the mitochondria?
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α-ketoglutarate dehydrogenase is an important branch point for amino acid metabolism.
α-ketoglutarate dehydrogenase is an important branch point for amino acid metabolism.
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What is the type of inhibition exhibited by other intermediates on rate-controlling enzymes?
What is the type of inhibition exhibited by other intermediates on rate-controlling enzymes?
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What type of bond is conserved in the oxidation process?
What type of bond is conserved in the oxidation process?
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The carbons in CO2 are originated from pyruvate.
The carbons in CO2 are originated from pyruvate.
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What is the product of the phosphoryl transfer reaction in Succinyl-CoA Synthetase?
What is the product of the phosphoryl transfer reaction in Succinyl-CoA Synthetase?
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The enzyme _______________ is responsible for the phosphorylysis of the thioester bond in Succinyl-CoA Synthetase.
The enzyme _______________ is responsible for the phosphorylysis of the thioester bond in Succinyl-CoA Synthetase.
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What is the role of the His residue in the active site of Succinyl-CoA Synthetase?
What is the role of the His residue in the active site of Succinyl-CoA Synthetase?
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GTP is a less energy-rich molecule than ATP.
GTP is a less energy-rich molecule than ATP.
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Match the following steps with their corresponding products:
Match the following steps with their corresponding products:
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What is the net result of the citric acid cycle after two pyruvates go through it?
What is the net result of the citric acid cycle after two pyruvates go through it?
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What is the function of the iron-sulfur center in aconitase?
What is the function of the iron-sulfur center in aconitase?
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Isocitrate dehydrogenase uses a Mn2+ ion cofactor.
Isocitrate dehydrogenase uses a Mn2+ ion cofactor.
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What is the product of the oxidative decarboxylation reaction in the α-ketoglutarate dehydrogenase complex?
What is the product of the oxidative decarboxylation reaction in the α-ketoglutarate dehydrogenase complex?
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The iron-sulfur center in aconitase regulates _________ in the cell.
The iron-sulfur center in aconitase regulates _________ in the cell.
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What is similar between the α-ketoglutarate dehydrogenase complex and the PDH complex?
What is similar between the α-ketoglutarate dehydrogenase complex and the PDH complex?
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The carbon lost as CO2 in the isocitrate dehydrogenase reaction originates from acetyl-CoA.
The carbon lost as CO2 in the isocitrate dehydrogenase reaction originates from acetyl-CoA.
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Match the enzyme with its function:
Match the enzyme with its function:
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What is the function of the manganese ion cofactor in isocitrate dehydrogenase?
What is the function of the manganese ion cofactor in isocitrate dehydrogenase?
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Study Notes
Iron-Sulfur Center in Aconitase
- Iron-sulfur center acts in both substrate binding and catalysis (dehydration and hydration)
- Aconitase regulates iron uptake and metabolism in the cell
Isocitrate Dehydrogenase
- Isocitrate dehydrogenase is an oxidation coupled to a hydride transfer to NAD+
- The enzyme uses a Mn2+ ion cofactor, enhancing the electron withdrawing power of the carbonyl and facilitating decarboxylation
- Carbon lost as CO2 is not originally from carbons in acetyl-CoA
α-KG Dehydrogenase Complex
- α-ketoglutarate dehydrogenase complex performs oxidative decarboxylation, splits the carbon-carbon bond, releases CO2, and reduces NAD+ to NADH
- Has a structure similar to PDH complex and also works similarly
- Has E1, E2, E3 and coenzymes TPP, lipoyllysine, CoA, FAD, and NAD+
- The energy of the oxidation is conserved in the form of a thioester bond
Similar Reactions
- Thioester bond is a high-energy bond with very negative free-energy of hydrolysis
- α-KG dehydrogenase complex and PDH complex share similarities
Origin of Carbon Atoms in CO2
- The carbons in CO2 originate from oxaloacetate, not from pyruvate
- Net complete oxidation of glucose occurs after two pyruvates go through the citric acid cycle
Succinyl-CoA Synthetase
- Succinyl-CoA synthetase performs phosphorylysis of the thioester bond, followed by phosphoryl transfer to GDP, producing succinate plus GTP
- Transfer of phosphate is mediated by His residue in the active site
- GTP is as good as ATP, with free conversion of NTPs in the cell
Succinate Dehydrogenase
- Succinate dehydrogenase converts succinate to fumarate, with reducing power transferred to FAD
- FADH2 yields 1.5 ATP
- Rate controlling enzymes: citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase
Regulation of Activity
- Regulation of activity: activated by substrate availability, inhibited by product accumulation
- Allosteric inhibition or activation by other intermediates
Other Regulation Mechanisms
- Citrate synthase is also inhibited by succinyl-CoA
- α-ketoglutarate is an important branch point for amino acid metabolism
- Succinyl-CoA communicates the flow at this branch point to the start of the cycle
- Inhibition of isocitrate dehydrogenase leads to accumulation of isocitrate, pushing the equilibrium towards citrate
- Accumulated citrate leaves mitochondria and inhibits phosphofructokinase-1 in glycolysis
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Description
This quiz covers the role of iron-sulfur centers in aconitase and isocitrate dehydrogenase enzymes in the citric acid cycle, including their functions in substrate binding, catalysis, and iron uptake regulation.
