<p>Aconitase (aconitate hydratase) [<cite idref="PUB00005471"/>] is the enzyme from the tricarboxylic acid cycle that catalyzes the reversible isomerization of citrate and isocitrate. Cis-aconitate is formed as an intermediary product during the course of the reaction. In eukaryotes two isozymes of aconitase are known to exist: one found in the mitochondrial matrix and the other found in the cytoplasm. Aconitase, in its active form, contains a 4Fe-4S iron-sulphur cluster; three cysteine residues have been shown to be ligands of the 4Fe-4S cluster. It has been shown that the aconitase family also contains the following proteins: </p><ul><li>Iron-responsive element binding protein (IRE-BP). IRE-BP is a cytosolic protein that binds to iron-responsive elements (IREs). IREs are stem-loop structures found in the 5'UTR of ferritin, and delta aminolevulinic acid synthase mRNAs, and in the 3'UTR of transferrin receptor mRNA. </li><li>3-isopropylmalate dehydratase (<db_xref db="EC" dbkey="4.2.1.33"/>) (isopropylmalate isomerase), the enzyme that catalyzes the second step in the biosynthesis of leucine. </li><li>Homoaconitase (<db_xref db="EC" dbkey="4.2.1.36"/>) (homoaconitate hydratase), an enzyme that participates in the alpha-aminoadipate pathway of lysine biosynthesis and that converts cis-homoaconitate into homoisocitric acid. </li><li>Esherichia coli protein YbhJ. </li></ul><p>The signatures in this entry, identify the cysteine residues involved in the binding of the 4Fe-4S iron-sulphur cluster. </p> Aconitase family, 4Fe-4S cluster binding site