Selective One-Electron Reduction of <i>Nitrosomonas europaea</i> Hydroxylamine Oxidoreductase with Nitric Oxide

Cabail, Maria Zulema; Pacheco, A. Andrew

doi:10.1021/ic025779n

Cited by 28 publications

(28 citation statements)

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“…The relative contributions of NorCB and the alternative N 2 O-producing pathway(s) cannot be deduced from the observations because of possible pleiotropic effects of the mutation of norB. NorCB did not play a vital role in the tolerance of N. europaea to NO 2 Ϫ or NO produced during growth on NH 3 . The relatively high NO tolerance was only compromised by the inactivation of norB in the presence of high concentrations of SNP, suggesting that an alternative NO-consuming mechanism might be present.…”

Section: Vol 186 2004 Notes 4419mentioning

confidence: 86%

“…The concentration of P. denitrificans cells that was used was approximately four times higher than that of N. europaea, OD 600 of 0.24 and 0.06, respectively. P. denitrificans was cultured under O 2 -limiting conditions in the presence of NO 3 Ϫ , to ensure the expression of both Nor and terminal oxidase (21). In contrast to N. europaea, the addition of 15 l of NO-saturated buffer resulted in a transient inhibition of the succinate-dependent O 2 uptake by both wild-type and NorB-deficient cells of P. denitrificans (data not shown).…”

Section: Vol 186 2004 Notes 4419mentioning

confidence: 99%

“…Denitrification is an anaerobic mode of respiration that involves the enzymes nitrate reductase, nitrite reductase (Nir), nitric oxide reductase, and nitrous oxide reductase, which catalyze the stepwise reduction of nitrate (NO 3 Ϫ ), via the intermediates nitrite (NO 2 Ϫ ), NO, and N 2 O, to dinitrogen (24). Accordingly, full expression of the denitrifying pathway in heterotrophic denitrifying bacteria occurs in response to a combination of oxygen (O 2 ) limitation and the presence of one, or more, of the denitrification substrates NO 3 Ϫ , NO 2 Ϫ , and NO (24). Recently, we reported the identification of a gene that encodes a copper-type nitrite reductase (NirK) in N. europaea (2).…”

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confidence: 99%

“…europaea acquires all its free energy from the oxidation of NH 3 to NO 2 Ϫ via the intermediate hydroxylamine (NH 2 OH), which is catalyzed by the enzymes ammonia monooxygenase and hydroxylamine oxidoreductase (HAO) (23). While this nitrification pathway is relatively well characterized, the structure, functioning, and physiological relevance of its putative denitrification pathway(s) still remain largely unknown (1,2,15,19,20).…”

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confidence: 99%

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Nitrosomonas europaea Expresses a Nitric Oxide Reductase during Nitrification

et al. 2004

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In this paper, we report the identification of a norCBQD gene cluster that encodes a functional nitric oxide reductase (Nor) in Nitrosomonas europaea. Disruption of the norB gene resulted in a strongly diminished nitric oxide (NO) consumption by cells and membrane protein fractions, which was restored by the introduction of an intact norCBQD gene cluster in trans. NorB-deficient cells produced amounts of nitrous oxide (N 2 O) equal to that of wild-type cells. NorCB-dependent activity was present during aerobic growth and was not affected by the inactivation of the putative fnr gene. The findings demonstrate the presence of an alternative site of N 2 O production in N. europaea.

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Section: Vol 186 2004 Notes 4419mentioning

confidence: 86%

Section: Vol 186 2004 Notes 4419mentioning

confidence: 99%

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confidence: 99%

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Nitrosomonas europaea Expresses a Nitric Oxide Reductase during Nitrification

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“…1B). Despite lacking homology to HAO (19,22), the presence of a P460 cofactor in cyt P460 has implicated this enzyme in NH 2 OH oxidation (23)(24)(25).…”

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Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission

Caranto

Vilbert

Lancaster

2016

Proc. Natl. Acad. Sci. U.S.A.

173

212

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Ammonia oxidizing bacteria (AOB) are major contributors to the emission of nitrous oxide (N 2 O). It has been proposed that N 2 O is produced by reduction of NO. Here, we report that the enzyme cytochrome (cyt) P460 from the AOB Nitrosomonas europaea converts hydroxylamine (NH 2 OH) quantitatively to N 2 O under anaerobic conditions. Previous literature reported that this enzyme oxidizes NH 2 OH to nitrite (NO − 2 ) under aerobic conditions. Although we observe NO − 2 formation under aerobic conditions, its concentration is not stoichiometric with the NH 2 OH concentration. By contrast, under anaerobic conditions, the enzyme uses 4 oxidizing equivalents (eq) to convert 2 eq of NH 2 OH to N 2 O. Enzyme kinetics coupled to UV/visible absorption and electron paramagnetic resonance (EPR) spectroscopies support a mechanism in which an Fe III -NH 2 OH adduct of cyt P460 is oxidized to an {FeNO} 6 unit. This species subsequently undergoes nucleophilic attack by a second equivalent of NH 2 OH, forming the N-N bond of N 2 O during a bimolecular, rate-determining step. We propose that NO − 2 results when nitric oxide (NO) dissociates from the {FeNO} 6 intermediate and reacts with dioxygen. Thus, NO − 2 is not a direct product of cyt P460 activity. We hypothesize that the cyt P460 oxidation of NH 2 OH contributes to NO and N 2 O emissions from nitrifying microorganisms. possesses a global warming potential nearly 300-fold greater than carbon dioxide (1). Atmospheric N 2 O concentrations have increased ∼120% since the preindustrial era, largely due to the widespread use of fertilizers required to produce sustenance for humans and livestock. N 2 O is a byproduct of the microbial metabolism of fertilizer components, including ammonia (NH 3 ) and nitrate (NO − 3 ); consequently, agricultural soils account for an estimated 60-75% of global N 2 O emissions. The metabolic pathway by which microorganisms oxidize NH 3 , nitrification, occurs in two phases, both of which are mediated by autotrophic microorganisms. In the first, NH 3 -oxidizing bacteria (AOB) or archaea (AOA) oxidize NH 3 to nitrite (NO − 2 ). In the second, NO − 2 is subsequently oxidized to NO − 3 by NO − 2 -oxidizing bacteria. NH 3 -oxidizing microbes contribute substantially to global N 2 O emissions, whereas NO − 2 -oxidizing bacteria produce negligible N 2 O (2, 3). AOB are proposed to emit N 2 O either as a byproduct of the nitrification pathway or as a product of the nitrifier denitrification pathway (i.e., the reduction of NO − 2 ) (4-6). Nitrification of NH 3 to NO − 2 occurs in two steps (7,8). The first step is catalyzed by NH 3 monooxygenase, which uses copper (Cu) and dioxygen (O 2 ) to hydroxylate NH 3 to hydroxylamine (NH 2 OH) (9). In AOB, the second step is thought to be the four-electron oxidation of NH 2 OH to NO − 2 by NH 2 OH oxidoreductase (HAO). HAO is a multiheme enzyme with eight c-type hemes per subunit: seven are electron transfer cofactors, and the eighth is the so-called P460 active site that contains a unique tyrosine cross-link to the ...

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Iron Porphyrin Chemistry

Walker¹,

Simonis²

2005

Encyclopedia of Inorganic Chemistry

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This article reviews most aspects of the chemistry of iron porphyrins, from Fe(0) to Fe(V), including occurrence and roles of natural iron porphyrins (hemes) and their synthetic analogs, structures and electron configurations of iron porphyrins of all oxidation and spin states, π electron configuration of the porphyrin ring, synthesis of metal‐free porphyrins and other related macrocycles, insertion of iron into free‐base porphyrins and related macrocycles, the properties, reactions, uses and biological relevance of iron(0), ‐(I), ‐(II) porphyrins (the latter with S = 0, 1, and 2 spin state possibilities), of iron(II) porphyrin π‐cation radicals, of iron(III) porphyrins (with S = 1/2, 3/2, and 5/2 spin state possibilities), of iron(III) porphyrin and corrole π‐cation radicals, of iron(IV) porphyrins (including five‐ and six‐coordinate ferryl (FeO) 2+ , iron(IV) phenyl, carbene and hydrazine complexes, and the bis‐methoxide complex) and a comparison of iron(IV) porphyrins to iron(III) porphyrin π‐cation radicals, of iron(IV) porphyrin π‐cation radicals, and of the possible existence of iron(V) porphyrins. Included in the Fe(II) part are sections on addition of ligands to four‐coordinate iron(II) porphyrins, including equilibrium binding constants, photodissociation of ligands from PFeL 2 complexes, binding of small molecules (O 2 , CO, NO, HNO) to 5‐coordinate iron(II) porphyrins and design of porphyrin ligands that will mimic the active sites of heme proteins such as myoglobin and hemoglobin, the cytochromes P450 and nitric oxide synthases, and the nitrophorins and guanylyl cyclases. Included in the iron(III) part are sections on both 5‐ and 6‐coordinate high‐spin complexes and their similarities and differences, bridged or through‐space magnetically coupled complexes of high‐spin iron(III) porphyrins with other metal complexes as possible models for cytochrome oxidase and the assimilatory sulfite reductases, coupled oxidation of hemes by hydrogen peroxide or its equivalent, and the relationship of this reactivity to the reactions of heme oxygenase, iron(III) porphyrins as reduction catalysts, and photochemistry of iron(III) porphyrins, possible electron configurations of low‐spin iron(III) porphyrins, the phenomenon and possible electronic consequences of ruffling of the porphinato core in iron(III) porphyrins, the preferred orientation of planar axial ligands bound to low‐spin iron(III) porphyrins, NO complexes of iron(III) porphyrins, reduction potentials, equilibrium constants and rates of axial‐ligand addition and exchange, kinetics of axial‐ligand rotation and porphyrin ring inversion, kinetics of reduction and autoreduction of iron(III) porphyrins, electron self‐exchange between low‐spin iron(III) and iron(II) porphyrins, synthetic ferriheme proteins, and synthesis of five‐coordinate low‐spin iron(III) porphyrins having σ‐alkyl or σ‐aryl groups as axial ligands. The iron(IV) and iron(IV) cation radical sections discuss the high‐valent states of cytochromes P450 and related enzymes.

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Selective One-Electron Reduction of Nitrosomonas europaea Hydroxylamine Oxidoreductase with Nitric Oxide

Cited by 28 publications

References 25 publications

Nitrosomonas europaea Expresses a Nitric Oxide Reductase during Nitrification

Nitrosomonas europaea Expresses a Nitric Oxide Reductase during Nitrification

Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission

Iron Porphyrin Chemistry

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