Fumarase (or fumarate hydratase) is an enzyme that catalyzes the reversible hydration/dehydration of Fumarate to S-malate. Fumarase comes in two forms: mitochondrial and cytosolic. The mitochondrial isoenzyme is involved in the Krebs Cycle (also known as the Citric Acid Cycle), and the cytosolic isoenzyme is involved in the metabolism of amino acids and fumarate. Subcellular localization is established by the presence of a signal sequence on the amino terminus in the mitochondrial form, while subcellular localization in the cytosolic form is established by the abence of the signal sequence found in the mitochondrial variety. This enzyme participates in 3 metabolic pathways: citric acid cycle, reductive carboxylation cycle (CO₂ fixation), and in renal cell carcinoma.