Aconitase (aconitate hydratase) contains an Fe-S cluster within the active site. This can be in the form 4Fe-4S in which case the enzyme functions as an aconitate hydratase, performing the dehydration-rehydration of citrate to isocitrate via cis-aconitate in the second and third steps of the Krebs cycle. When the Fe-S cluster is in the form 3Fe-4S (cytosolic aconitase) the enzyme functions as an Iron Regulatory Protein (IRP) which binds to a conserved sequence (Iron Responsive Element; IRE) in mRNAs encoding proteins that function in the maintenance of iron homeostasis thus regulating the translation of that mRNA. Aconitase occurs in bacteria, plants, animals and fungi in mitochondrial and cytosolic forms.
Defined by 6 residues: ASP:A-100HIS:A-101ASP:A-165ARG:A-447SER:A-642ARG:A-644