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Aconitase



 

aconitase 1, soluble
Identifiers
Symbol ACO1
Alt. Symbols IREB1
Entrez 48
HUGO 117
OMIM 100880
RefSeq NM_002197
UniProt P21399
Other data
EC number 4.2.1.3
Locus Chr. 9 p21.1
aconitase 2, mitochondrial
Identifiers
Symbol ACO2
Entrez 50
HUGO 118
OMIM 100850
RefSeq NM_001098
UniProt Q99798
Other data
EC number 4.2.1.3
Locus Chr. 22 q13.2

Additional recommended knowledge

Aconitase (aconitate hydratase; EC 4.2.1.3) is an enzyme that catalyses the stereo-specific isomerization of citrate to isocitrate via cis-aconitate in the tricarboxylic acid cycle, a non-redox-active process.

Function

By contrast with the majority of iron-sulfur proteins that function as electron carriers, the iron-sulfur cluster of aconitase reacts directly with an enzyme substrate. Aconitase has an active [Fe4S4]2+ cluster, which may convert to an inactive [Fe3S4]+ form. Three cysteine (Cys) residues have been shown to be ligands of the [Fe4S4] centre. In the active state, the labile iron ion of the [Fe4S4] cluster is not coordinated by Cys but by water molecules.

The iron-responsive element binding protein (IRE-BP) and 3-isopropylmalate dehydratase (α-isopropylmalate isomerase; EC 4.2.1.33), an enzyme catalysing the second step in the biosynthesis of leucine, are known aconitase homologues. Iron regulatory elements (IREs) constitute a family of 28-nucleotide, non-coding, stem-loop structures that regulate iron storage, heme synthesis and iron uptake. They also participate in ribosome binding and control the mRNA turnover (degradation). The specific regulator protein, the IRE-BP, binds to IREs in both 5' and 3' regions, but only to RNA in the apo form, without the Fe-S cluster. Expression of IRE-BP in cultured cells has revealed that the protein functions either as an active aconitase, when cells are iron-replete, or as an active RNA-binding protein, when cells are iron-depleted. Mutant IRE-BPs, in which any or all of the three Cys residues involved in Fe-S formation are replaced by serine, have no aconitase activity, but retain RNA-binding properties.

Aconitase is inhibited by fluoroacetate, therefore fluoroacetate is poisonous.

References

  • Beinert, H., Kennedy, M.C. and Stout, C.D. (1996). "Aconitase as iron-sulfur protein, enzyme, and iron-regulatory protein". Chem. Rev. 96: 2335–2373.
  • Flint, D.H. and Allen, R.M. (1996). "Iron-sulfur proteins with nonredox functions". Chem. Rev. 96: 2315–2334.
  • Frishman, D. and Hentze, M.W. (1996). "Conservation of aconitase residues revealed by multiple sequence analysis". Eur. J. Biochem. 239: 197–200.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Aconitase". A list of authors is available in Wikipedia.
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