Which of the following is an inhibitor of citrate synthase?

Citrate synthase is an important enzyme in the citric acid cycle, responsible for catalyzing the first step of the pathway by condensing acetyl-CoA with oxaloacetate to form citrate. The regulation of citrate synthase is influenced by several metabolites, which indicates the energy status of the cell.

High NADH levels indicate a high availability of reducing equivalents and energy, which suggests that the cell might not need to process more substrates through the citric acid cycle for energy production. In this situation, the presence of high NADH acts as an inhibitory signal, slowing down the activity of citrate synthase to prevent excessive citrate production when aerobic respiration is already sufficiently generating ATP. This feedback mechanism helps maintain energy balance within the cell by regulating the flow of metabolites based on current energy needs.

While ATP and other factors like ADP and GDP can influence the activity of various enzymes in the citric acid cycle, in this specific context, the high levels of NADH effectively signal that the pathway should be downregulated, making it a key inhibitor of citrate synthase.