Calcium ions serve as a key signal linking energy demand to TCA cycle activation in muscle. Which enzymes of the TCA cycle are directly activated by increased mitochondrial Ca2+ concentration?

• A Isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and pyruvate dehydrogenase phosphatase ✓
• B Citrate synthase, aconitase, and succinate dehydrogenase
• C Malate dehydrogenase, fumarase, and succinyl-CoA synthetase
• D Citrate synthase, isocitrate dehydrogenase, and succinate dehydrogenase

Explanation

Mitochondrial Ca2+ directly activates isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase (by decreasing their Km for substrates) and activates pyruvate dehydrogenase phosphatase (which dephosphorylates and activates pyruvate dehydrogenase). This trio increases flux through the TCA cycle during increased workload. Distractor B is wrong because citrate synthase and aconitase are not Ca2+-activated.

Reference: Lehninger Principles of Biochemistry, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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