Time-Resolved Resonance Raman and Time-Resolved Step-Scan FTIR Studies of Nitric Oxide Reductase from Paracoccus denitrificans: Comparison of the Heme b3-FeB Site to That of the Heme-CuB in Oxidases

Pinakoulaki, Eftychia; Varotsis, Constantinos

doi:10.1021/bi035289m

Cited by 33 publications

(36 citation statements)

References 24 publications

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“…cNOR. 11,105,108 The ν(CO) at 2068 cm −1 (Δ 13 CO = −47 cm −1 ) is consistent with a non-heme iron-CO where the back-bonding donation from the iron d π orbitals to the carbonyl π* orbitals is weakened compared to its heme-CO counterparts. The comparable integrated area of these two bands suggests that these two species are present in equivalent concentrations.…”

Section: The Diiron Site Can Accommodate Two Co Moleculesmentioning

confidence: 70%

Spectroscopic characterization of heme iron–nitrosyl species and their role in NO reductase mechanisms in diiron proteins

Moënne‐Loccoz

2007

Nat. Prod. Rep.

121

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Nitric oxide (NO) plays an important role in cell signalling and in the mammalian immune response to infection. On its own, NO is a relatively inert radical, and when it is used as a signalling molecule, its concentration remains within the picomolar range. However, at infection sites, the NO concentration can reach the micromolar range, and reactions with other radical species and transition metals lead to a broad toxicity. Under aerobic conditions, microorganisms cope with this nitrosative stress by oxidizing NO to nitrate (NO 3 − ). Microbial hemoglobins play an essential role in this NO-detoxifying process. Under anaerobic conditions, detoxification occurs via a 2-electron reduction of two NO molecules to N 2 O. In many bacteria and archaea, this NOreductase reaction is catalyzed by diiron proteins. Despite the importance of this reaction in providing microorganisms with a resistance to the mammalian immune response, its mechanism remains ill-defined. Because NO is an obligatory intermediate of the denitrification pathway, respiratory NO reductases also provide resistance to toxic concentrations of NO. This family of enzymes is the focus of this review. Respiratory NO reductases are integral membrane protein complexes that contain a norB subunit evolutionarily related to subunit I of cytochrome c oxidase (CcO). NorB anchors one high-spin heme b 3 and one non-heme iron known as Fe B , i.e., analogous to Cu B in CcO. A second group of diiron proteins with NO-reductase activity is comprised of the large family of soluble flavoprotein A found in strict and facultative anaerobic bacteria and archaea. These soluble detoxifying NO reductases contain a non-heme diiron cluster with a Fe-Fe distance of 3.4 Å and are only briefly mentioned here as a promising field of research. This article describes possible mechanisms of NO reduction to N 2 O in denitrifying NO-reductase (NOR) proteins and critically reviews recent experimental results. Relevant theoretical model calculations and spectroscopic studies of the NO-reductase reaction in heme/copper terminal oxidases are also overviewed.

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Section: The Diiron Site Can Accommodate Two Co Moleculesmentioning

confidence: 70%

Spectroscopic characterization of heme iron–nitrosyl species and their role in NO reductase mechanisms in diiron proteins

Moënne‐Loccoz

2007

Nat. Prod. Rep.

121

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“…The sequence of NorB contains all six histidines which are the ligands of heme a, heme a 3 and Cu B in cytochrome c oxidase [1][2][3][4][5]. Resonance Raman (RR) and time-resolved RR have revealed the properties of the dinuclear center of oxidized, reduced, CO-and NO-bound Nor from Paracoccus denitrificans [11,17,18]. The spectra of the oxidized enzyme showed two distinct m as (Fe-O-Fe) modes at 813 and 833 cm À1 that have been attributed to two different conformations (open and closed) of the catalytic site of the enzyme [11].…”

Section: Introductionmentioning

confidence: 99%

Nitric oxide activation and reduction by heme–copper oxidoreductases and nitric oxide reductase

Pinakoulaki

Varotsis

2008

Journal of Inorganic Biochemistry

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“…Despite extensive studies using spectroscopic (18 -26), kinetic (27)(28)(29)(30), and mutagenetic methods (31), the molecular mechanism of the NO reduction reaction catalyzed by NOR has not yet been established. Thus far, two mechanisms have been proposed, each assuming a different structure of the binuclear center (heme b 3 and Fe B ) in the intermediate state of the NO reduction (Scheme 1).…”

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confidence: 99%

NO Reduction by Nitric-oxide Reductase from Denitrifying Bacterium Pseudomonas aeruginosa

Kumita

Matsuura

Hino

et al. 2004

Journal of Biological Chemistry

100

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Nitric-oxide reductase (NOR) of a denitrifying bacterium catalyzes NO reduction to N 2 O at the binuclear catalytic center consisting of high spin heme b 3 and non-heme Fe B . The structures of the reaction intermediates in the single turnover of the NO reduction by NOR from Pseudomonas aeruginosa were investigated using optical absorption and EPR spectroscopies combined with an originally designed freeze-quench device. In the EPR spectrum of the sample, in which the fully reduced NOR was mixed with an NO solution and quenched at 0.5 ms after the mixing, two characteristic signals for the ferrous Fe B -NO and the penta-coordinated ferrous heme b 3 -NO species were observed. The CO inhibition of its formation indicated that two NO molecules were simultaneously distributed into the two irons of the same binuclear center of the enzyme in this state. The time-and temperature-dependent EPR spectral changes indicated that the species that appeared at 0.5 ms is a transient reaction intermediate prior to the N 2 O formation, in good agreement with the so-called "trans" mechanism. It was also found that the final state of the enzyme in the single turnover cycle is the fully oxidized state, in which the -oxo-bridged ligand is absent between the two irons of its binuclear center, unlike the resting form of NOR as isolated. On the basis of these present findings, we propose a newly developed mechanism for the NO reduction reaction conducted by NOR. Nitric-oxide reductase (NOR)1 is a metal-containing enzyme involved in biological denitrification processes. The enzyme catalyzes the two-electron reduction of nitric oxide (NO) to nitrous oxide (N 2 O) according to Equation 1 (1-4). Since the NO reduction reaction involves the N-O bond cleavage and the N-N bond formation, it is chemically interesting to elucidate the molecular mechanism of the NO reduction catalyzed by the metal enzymes.

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Time-Resolved Resonance Raman and Time-Resolved Step-Scan FTIR Studies of Nitric Oxide Reductase from Paracoccus denitrificans: Comparison of the Heme b₃-Fe_B Site to That of the Heme-Cu_B in Oxidases

Cited by 33 publications

References 24 publications

Spectroscopic characterization of heme iron–nitrosyl species and their role in NO reductase mechanisms in diiron proteins

Spectroscopic characterization of heme iron–nitrosyl species and their role in NO reductase mechanisms in diiron proteins

Nitric oxide activation and reduction by heme–copper oxidoreductases and nitric oxide reductase

NO Reduction by Nitric-oxide Reductase from Denitrifying Bacterium Pseudomonas aeruginosa

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