The domain structure and iron coordination of the Rieske domain is very similar to that of the cytochrome bc1 domain. The active-site iron center of one of the alpha subunits is directly connected by hydrogen bonds through a single amino acid, Asp205, to the Rieske [2Fe-2S] center in a neighboring alpha subunit. This is likely to be the main route for electron transfer.

Binding of oxygen to iron is exploited in several biological and chemical processes. Although computational and spectroscopic results have suggested side-on binding, only end-on binding of oxygen to iron has been observed in crystal structures. We have determined structures of naphthalene dioxygenase that show a molecular oxygen species bound to the mononuclear iron in a side-on fashion. In a complex with substrate and dioxygen, the dioxygen molecule is lined up for an attack on the double bond of the aromatic substrate. The structures reported here provide the basis for a reaction mechanism and for the high stereospecificity of the reaction catalyzed by naphthalene dioxygenase.

No abstract

A fragment of plasmid NAH7 from Pseudomonas putida PpG7 has been cloned and expressed in Escherichia coli HB101. Growth of the recombinant Escherichia coli in nutrient medium results in the formation of indigo. The production of this dye is increased in the presence of tryptophan or indole. Several bacteria that oxidize aromatic hydrocarbons to cis-dihydrodiols also oxidize indole to indigo. The results suggest that indigo formation is due to the combined activities of tryptophanase and naphthalene dioxygenase.

Naphthalene 1,2-dioxygenase (NDOS) is a three-component enzyme that catalyzes cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene formation from naphthalene, O 2 , and NADH. We have determined the conditions for a single turnover of NDOS for the first time and studied the regulation of catalysis. As isolated, the ␣ 3 ␤ 3 oxygenase component (NDO) has up to three catalytic pairs of metal centers (one mononuclear Fe 2؉ and one diferric Rieske iron-sulfur cluster). This form of NDO is unreactive with O 2 . However, upon reduction of the Rieske cluster and exposure to naphthalene and O 2 , ϳ0.85 cisdiol product per occupied mononuclear iron site rapidly forms. Substrate binding is required for oxygen reactivity. Stopped-flow and chemical quench analyses indicate that the rate constant of the single turnover product-forming reaction significantly exceeds the NDOS turnover number. UV-visible and electron paramagnetic resonance spectroscopies show that during catalysis, one mononuclear iron and one Rieske cluster are oxidized per product formed, satisfying the two-electron reaction stoichiometry. The addition of oxidized or reduced NDOS ferredoxin component (NDF) increases both the product yield and rate of oxidation of formerly unreactive Rieske clusters. The results show that NDO alone catalyzes dioxygenase chemistry, whereas NDF appears to serve only an electron transport role, in this case redistributing electrons to competent active sites.Rieske nonheme iron dioxygenases catalyze a remarkable reaction in which dioxygen is cleaved and both atoms are inserted across a double bond of an unactivated aromatic nucleus to yield a cis-dihydrodiol (1-4). These enzymes initiate the biodegradation of some of the most recalcitrant aromatic compounds that enter the environment from both natural and industrial sources, making their study of great importance for progress in bioremediation practices (5, 6). In addition, the inherent enantio-and regiospecificity of these enzymes make them useful for synthetic applications (7,8). Several of these multicomponent dioxygenases are known that differ in the number of components and the number and type of subunits in the oxygenase component that contains the active site. However, all of the enzyme systems share the common features of a reductase component that can accept and pass on two electrons from reduced pyridine nucleotide, an electron transport system that may be encompassed into the reductase, and an oxygenase that has both Rieske [2Fe-2S] clusters and mononuclear iron centers.One of the most thoroughly studied of the Rieske nonheme iron dioxygenases is naphthalene 1,2-dioxygenase (NDOS) 1 isolated from Pseudomonas sp. NCIB 9816-4, which catalyzes the reaction shown in Scheme 1 to yield (ϩ)-cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene (9).The complete NDOS consists of three protein components: the 36-kDa reductase protein (NDR) that contains a FAD molecule and a plant-type [2Fe-2S] cluster, the 14-kDa ferredoxin electron transfer protein (NDF) that contains a [2Fe-2S] Rieske cluster, an...

No abstract

Washed cell suspensions of Pseudomonas putida, grown with toluene as sole source of carbon, oxidized benzene, toluene, and ethylbenzene, at equal rates. Cell extracts were used to study benzene degradation and were shown to require nicotinamide-adenine dinucleotide, ethanol, ferrous ions, and L-cysteine for maximal activity. The benzene oxygenase system

No abstract