Which step directly follows the formation of citrate in the citric acid cycle?

• A. Aconitase reaction
• B. Isocitrate formation
• C. Pyrvate decarboxylation
• D. Fumarate formation

Answer: (A)

The step that directly follows the formation of citrate in the citric acid cycle is the aconitase reaction. After citrate is formed from acetyl-CoA and oxaloacetate, it undergoes a rearrangement catalyzed by the enzyme aconitase. This reaction converts citrate into isocitrate through an intermediate known as cis-aconitate. The aconitase reaction is crucial as it prepares the substrate for subsequent transformations in the cycle, leading eventually to the production of energy-dense molecules like NADH and FADH2. This role of aconitase emphasizes the importance of specific enzyme-catalyzed conversions in metabolic pathways and showcases the cyclic nature of the citric acid cycle, wherein each compound is systematically transformed to harvest energy efficiently.