What are the key enzymes involved in the citric acid cycle?

The key enzymes involved in the citric acid cycle are citrate synthase, aconitase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase.

The citric acid cycle, also known as the Krebs cycle or the tricarboxylic acid cycle, is a series of chemical reactions used by all aerobic organisms to generate energy. This cycle involves several key enzymes that catalyse specific reactions.

Citrate synthase is the first enzyme in the citric acid cycle. It catalyses the condensation of acetyl CoA and oxaloacetate to form citrate. This reaction is highly exergonic, meaning it releases a large amount of energy, which drives the reaction forward.

Aconitase is the next enzyme in the cycle. It catalyses the isomerisation of citrate to isocitrate. This is a reversible reaction, meaning it can proceed in both directions. However, in the citric acid cycle, it usually proceeds in the direction of isocitrate formation.

Isocitrate dehydrogenase is another key enzyme in the citric acid cycle. It catalyses the oxidative decarboxylation of isocitrate, producing α-ketoglutarate and CO2. This reaction is also highly exergonic and is one of the key regulatory steps in the cycle.

Finally, α-ketoglutarate dehydrogenase catalyses the second oxidative decarboxylation in the cycle, converting α-ketoglutarate to succinyl CoA and CO2. This reaction is similar to the one catalysed by isocitrate dehydrogenase and is another key regulatory step in the cycle.

These enzymes are crucial for the functioning of the citric acid cycle. They catalyse specific reactions that allow the cycle to proceed, generating energy for the cell. Without these enzymes, the cycle would not be able to function, and aerobic organisms would not be able to generate energy efficiently.