Rieske oxygenases

Naphthalene dioxygenase consists of three components, which form an electron transfer chain an NADH-dependent flavoprotein reductase, a ferredoxin containing two [2Fe2S] Rieske iron-sulfur clusters, and a Rieske oxygenase containing both a [2Fe2S] Rieske iron-sulfiir cluster and a mononuclear iron(II) center in the enzyme active site. ° ... 

In the past 15-20 years, several studies have been performed on mononuclear non-heme iron(II) enzymes. Among them, Rieske oxygenases constitute a relevant and paradigmatic example of mononuclear non-heme iron(II) proteins involved in O2 activation reactions. Their efficiency and versatility are even greater than those of the related heme-containing Cyt P450, being able to catalyze stereoselective... 

Scheme 2 Benzylic hydroxylation and aromatic cw-dihydroxylation reactions catalyzed by Rieske oxygenases (toluene monooxygenase and naphthalene-1,2-dioxygenase, respectively)...

Rieske oxygenases are part of a superfamily of enzymes that share a characteristic structure consisting of an oxygenase component (a mononuclear non-heme iron(II) high spin center containing a 2-His-l-carboxylate facial triad motif in the active site) [31-33]. Besides, the active site contains a reductase component (an Fe2-S2 Rieske center) that delivers electrons from NAD(P)H to the oxygenase center [34]. 

A different approach was proposed by Hooley and coworkers [72], In this study resorcinarene-based cavitands were used as catalysts, which allow for binding of iron(II) by bidentate ligands, leaving empty sites for further reactivity at the metal sites. The iron-coordinated cavitands 7bFe2 and 12bFe (Scheme 30) bore free coordination sites, and thus they were envisioned to perform C-H oxidation reactions under mild conditions, inspired by the mode of action of the Rieske oxygenases. However, these catalysts proved inactive towards cyclohexane and methylcyclohexane oxidations. In contrast, they were able to convert fluorene smoothly to fluorenone using TBHP as oxidant. 

Sequences of proteins containing Rieske-type clusters have been deduced from the complete operons of several dioxygenases these dioxygenases require electrons from NAD(P)H to convert aromatic compounds to cis-arene diols. The water-soluble dioxygenase systems consist of a reductase and a terminal dioxygenase many dioxygenases also contain a [2Fe-2S] ferredoxin (20). The terminal oxygenases contain a Rieske-type cluster and the ferredoxins may contain either a Rieske-type or a 4-cysteine coordinated [2Fe-2S] cluster. 

Proteins from Eukaryotes that Show Homology to Bacterial Rieske-Type Oxygenases... 

Lee J, M Simurdiak, H Zhao (2005) Reconstitution and characterization of aminopyrrolnitrin oxygenase, a Rieske iV-oxygenase that catalyzes unusual arylamine oxidation. J Biol Chem 280 36719-36727. 

Limitations of Stmctural Studies. EXAFS is not well suited for identifying weak scatterers, (e.g. oxygen in the presence of sulfur) as illustrated by recent data for the Rieske-like site in P. cepacia phthalate oxygenase (26). This site is believed to contain... 

D. J. Ferraro, L. Gakhar, S. Ramaswamy, Rieske business Structure-function of Rieske non-heme oxygenases, Biochem. Biophys. Res. Commun. 338 (2005) 175. 

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