Which enzyme catalyzes the conversion of acetyl-CoA and oxaloacetate to citrate?

The conversion of acetyl-CoA and oxaloacetate to citrate is catalyzed by citrate synthase. This enzyme plays a crucial role in initiating the citric acid cycle, also known as the Krebs cycle. During this reaction, acetyl-CoA, derived from carbohydrates, fats, and proteins, combines with oxaloacetate to form citrate. This step is significant because it marks the entry point of the acetyl group into the cycle, facilitating the subsequent reactions that lead to the production of energy in the form of ATP, NADH, and FADH2.

Citrate synthase operates through a mechanism that not only brings these two substrates together but also undergoes conformational changes to stabilize the transition state, ensuring an efficient reaction. The formation of citrate from acetyl-CoA and oxaloacetate highlights the importance of this enzyme in the overall metabolic pathway, thus making it a key regulator of the citric acid cycle.