Which molecule acts as a key allosteric inhibitor of citrate synthase?

The correct answer is NADH, which acts as a key allosteric inhibitor of citrate synthase. Citrate synthase is the enzyme responsible for catalyzing the condensation of acetyl-CoA and oxaloacetate to form citrate, marking the first step in the citric acid cycle. NADH serves as an important indicator of the cellular energy state; high levels of NADH suggest that the cell has ample energy and the citric acid cycle does not need to produce more energy at that moment.

By inhibiting citrate synthase, NADH helps to regulate the flow of metabolites through the citric acid cycle, ensuring that energy production is matched to the cell’s needs. This feedback mechanism helps to prevent the over-accumulation of intermediates and balances metabolic pathways based on energy demand.

While the other molecules listed can play various roles in metabolic pathways, they do not serve as key allosteric inhibitors of citrate synthase. FADH2 is primarily involved in the electron transport chain, ATP is generally known for being a product of energy metabolism rather than an inhibitor in this context, and CoA is mainly a carrier of acyl groups and plays a vital role in the formation of acetyl-CoA but does not inhibit citrate