Which compound is an intermediary substrate formed from succinate during the cycle?

The compound that is formed as an intermediary substrate from succinate during the citric acid cycle is fumarate. This reaction occurs when succinate is oxidized by the enzyme succinate dehydrogenase, leading to the conversion of succinate into fumarate. During this process, FAD (flavin adenine dinucleotide) is reduced to FADH2, which subsequently plays a role in the electron transport chain to contribute to ATP production.

Fumarate is an important cyclic intermediate that eventually gets converted to malate through the addition of a water molecule, catalyzed by the enzyme fumarase. Understanding this transformation is key to grasping how the cycle progresses and the series of chemical reactions that contribute to the overall metabolic pathway.

The other compounds listed do have roles within the citric acid cycle, but they are not directly formed from succinate. Citrate is formed from acetyl-CoA and oxaloacetate, oxaloacetate is regenerated at the end of the cycle, and malate is formed from fumarate in the subsequent step. This emphasizes the specific role of fumarate as an intermediary formed directly from succinate.