Concept

Fumarase

Summary
Fumarase (or fumarate hydratase) is an enzyme () that catalyzes the reversible hydration/dehydration of fumarate to malate. Fumarase comes in two forms: mitochondrial and cytosolic. The mitochondrial isoenzyme is involved in the Krebs 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 absence of the signal sequence found in the mitochondrial variety. This enzyme participates in 2 metabolic pathways: citric acid cycle and reductive citric acid cycle (CO2 fixation), and is also important in renal cell carcinoma. Mutations in this gene have been associated with the development of leiomyomas in the skin and uterus in combination with renal cell carcinoma (HLRCC syndrome). This enzyme belongs to the family of lyases, specifically the hydro-lyases, which cleave carbon-oxygen bonds. The systematic name of this enzyme class is (S)-malate hydro-lyase (fumarate-forming). Other names in common use include: fumarase L-malate hydro-lyase (S)-malate hydro-lyase In humans, the FH gene is localized to the chromosomal position 1q42.3-q43. The FH gene contains 10 exons. Crystal structures of fumarase C from Escherichia coli have been observed to have two dicarboxylate binding sites close to one another. These are known as the active site and the B site. These sites are connected by a series of hydrogen bonds and the access to either site is only through an opening near the enzyme surface near the B site. Active site is made up of three domains. Even when no ligand is bound to the active site, the binding pocket created by surrounding residues is sufficient to bind water in its place. Crystallographic research on the B site of the enzyme has observed that there is a shift on His129 between free and occupied states. It also suggests that the use of an imidazole-imidazolium conversion controls access to the allosteric B site.
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