Succinate is first oxidized in a dehydrogenation reaction (catalyzed by succinate dehydrogenase), converting succinate into an alkene, fumarate. This oxidiation reduces FAD into FADH2.

Fumarate is then hydrated to form the alcohol malate, which is then oxidized to form the aldehyde, oxaloacetate, converting NAD+ to NADH. Oxaloacetate is the form which initial combined with acetyl CoA, so the cycle is complete.