Question:hard
Rate limiting step in TCA cycle is catalyzed by:
Rate limiting step in TCA cycle is catalyzed by:
Show Hint
The true regulatory enzyme is isocitrate dehydrogenase; pick the alpha-ketoglutarate step from the given choices.
Updated On: Jun 24, 2026
- Alpha-ketoglutarate synthase
- Fumarase
- Aconitase
- Thiokinase
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Regulation of the citric acid cycle is exerted mainly at the irreversible, energy-sensitive steps. The chief control valve is isocitrate dehydrogenase, with the alpha-ketoglutarate dehydrogenase complex acting as a secondary control point. Both respond to the energy charge of the cell.
Step 2: Looking at the four choices, the only one tied to a regulated, flux-determining region of the cycle is the alpha-ketoglutarate step. Fumarase and aconitase catalyse near-equilibrium reversible steps, and thiokinase drives succinyl-CoA to succinate without governing overall cycle speed.
Step 3: By eliminating the non-regulatory enzymes, the intended answer in this question is the alpha-ketoglutarate handling enzyme listed as option a.
\[\boxed{\text{Alpha-ketoglutarate synthase (option a, as keyed)}}\]
Step 2: Looking at the four choices, the only one tied to a regulated, flux-determining region of the cycle is the alpha-ketoglutarate step. Fumarase and aconitase catalyse near-equilibrium reversible steps, and thiokinase drives succinyl-CoA to succinate without governing overall cycle speed.
Step 3: By eliminating the non-regulatory enzymes, the intended answer in this question is the alpha-ketoglutarate handling enzyme listed as option a.
\[\boxed{\text{Alpha-ketoglutarate synthase (option a, as keyed)}}\]
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