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UNDER CONSTRUCTION

Aconitase (ACO) is an enzymatic domain that confers the ability to catalyse the equilibrium

citrate = aconitate + H₂O = L-isocitrate

This reaction is part of the citrate (TCA-, Krebs-)cycle.

In most organims, there is a cytosolic enzyme with an ACO domain (cAc), and in eukaryotes, a second copy of it was introduced with mitochondria (mAc). Plants developed even more copies in mitochondria.

Contents 1 Catalytic mechanism of mitochondrial ACO 2 Cytosolic aconitase and its other function 3 Literature 4 References 5 External links

Catalytic mechanism of mitochondrial ACO

spinqualitylabelsall models Mitochondrial aconitase from pig, PDB 7acn. Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Both mAc and cAc are quite similar in their ACO function. Studies, however, concentrated on . ACO is an excellent system for understanding the role of iron-sulfur-clusters in catalysis. The by three sulfur atoms belonging to the cysteins-385, -448, and -451 cluster iron atoms. On activation of the enzyme, . It can be four-, five-, or six-coordinate, but is constrained to bond to three sulfur atoms of the (4Fe-4S)-cluster with tetrahedral geometry. Thus, Fe4 is free to bind one, two, or three partners, in this reaction always oxygen atoms belonging to other molecules. As Fe4 is not bound very fast to the cluster, it moves quite a bit around in the process of bonding and debonding.^[1]

Cytosolic aconitase and its other function

spinqualitylabelsall models Cytosolic aconitase from rabbit (bound to RNA) and human (with Fe4S4 cluster), from PDB 2ipy and 2b3x. Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

A specialty of cAc is that in mammals it has developed a as inhibitor of that carry an . Therefore, the cytosolic cAc is named IREBP for IRE-binding protein when this function is talked about. Only one of the two functions is active, depending on whether is present in the molecule: it's essential for . You can see, by , how much the enzyme structure differs between those two functions.

Literature

• M. Claire Kennedy and Helmut Beinert: IX.4. Aconitase. in Ivano Bertini, Harry B. Gray, Edward I. Stiefel, Joan Selverstone Valentine (eds.): Biological Inorganic Chemistry: Structure and Reactivity. University Science Books, Herndon 2006. ISBN 1891389432 pp.209--

References

1. ↑ Lauble H, Kennedy MC, Beinert H, Stout CD. Crystal structures of aconitase with trans-aconitate and nitrocitrate bound. J Mol Biol. 1994 Apr 8;237(4):437-51. PMID:8151704 doi:http://dx.doi.org/10.1006/jmbi.1994.1246

External links

• Molecule of the Month: Aconitase and Iron Regulatory Protein 1
• Aconitase at Wikipedia