Which step of the Citric Acid Cycle involves the transformation of isocitrate to α-ketoglutarate?

The transformation of isocitrate to α-ketoglutarate occurs specifically in Step 3 of the Citric Acid Cycle, also known as the Krebs cycle. This step is catalyzed by the enzyme isocitrate dehydrogenase.

During this reaction, isocitrate undergoes oxidative decarboxylation, where it loses a carbon atom in the form of carbon dioxide (CO₂) and is oxidized to form α-ketoglutarate. Additionally, this process involves the reduction of NAD⁺ to NADH, a key energy-carrying molecule. The generation of NADH during this step contributes to the overall energy yield of the cycle, as NADH can later participate in oxidative phosphorylation to produce ATP.

The correct identification of this step is crucial for understanding the overall functioning of the Citric Acid Cycle and its role in cellular respiration.