What allosteric regulators activate the isocitrate dehydrogenase enzyme?

The activation of the isocitrate dehydrogenase enzyme is crucial for the regulation of the citric acid cycle, and it is notably influenced by specific allosteric regulators. ADP and calcium ions serve as important signals indicating the energy status of the cell. When ADP levels rise, it signifies that the cell is in need of more ATP, thus stimulating the activity of isocitrate dehydrogenase to enhance the flux through the citric acid cycle and increase the production of ATP.

Similarly, calcium ions are an important signaling molecule, especially in muscle cells and other tissues where energy demand rises. Elevated calcium levels can indicate increased cellular activity and also promote the activation of isocitrate dehydrogenase, again contributing to enhanced ATP production.

In this context, ADP and calcium ions not only act as indicators of energy deficiency but also play direct roles in enhancing the enzymatic activity of isocitrate dehydrogenase, thereby facilitating the continuation of the citric acid cycle under conditions where energy is required.

The other choices involve regulators that do not play a significant role in the activation of isocitrate dehydrogenase or function differently in the metabolic pathways.