Hydroxylamine oxidoreductase

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Hydroxylamine Oxidoreductase
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EC no. 1.7.3.4
CAS no. 9075-43-8
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Hydroxylamine oxidoreductase (HAO) is an enzyme found in the prokaryotic genus Nitrosomonas. It plays a critically important role in the biogeochemical nitrogen cycle as part of the metabolism of ammonia-oxidizing bacteria.

Contents

The substrate is hydroxylamine (), a chemical produced biologically by the enzyme Ammonia monooxygenase. The products of the catalyzed reaction are debated, but recent work shows compelling evidence for the production of nitric oxide. [1]

Structural studies

Crystallographic methods show that HAO (PDB code: 1FGJ) is a cross-linked trimer of polypeptides containing 24 heme cofactors. [2] [3]

Reactivity

For many decades the enzyme was thought to catalyze the following reaction: [4]

Recent work in the field, however, reveals that this enzyme catalyzes an entirely different reaction: [1]

Subsequent oxidation of the nitric oxide to nitrite caused by reaction with oxygen accounts for the reactivity previous described by Hooper et al.

Environmental Impact

Nitric oxide, the product of HAO catalysis, is a potent greenhouse gas. [5] Additionally, the oxidized product of nitric oxide in the presence of oxygen is nitrite - a common pollutant in agricultural run-off.

Related Research Articles

<span class="mw-page-title-main">Hemoprotein</span> Protein containing a heme prosthetic group

A hemeprotein, or heme protein, is a protein that contains a heme prosthetic group. They are a very large class of metalloproteins. The heme group confers functionality, which can include oxygen carrying, oxygen reduction, electron transfer, and other processes. Heme is bound to the protein either covalently or noncovalently or both.

<span class="mw-page-title-main">Hydroxylamine</span> Inorganic compound

Hydroxylamine is an inorganic compound with the formula NH2OH. The material is a white crystalline, hygroscopic compound. Hydroxylamine is almost always provided and used as an aqueous solution. It is consumed almost exclusively to produce Nylon-6. The oxidation of NH3 to hydroxylamine is a step in biological nitrification.

<span class="mw-page-title-main">Nitrification</span> Biological oxidation of ammonia/ammonium to nitrate

Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil. Nitrification is an aerobic process performed by small groups of autotrophic bacteria and archaea.

Nitrosomonas europaea is a Gram-negative obligate chemolithoautotroph that can derive all its energy and reductant for growth from the oxidation of ammonia to nitrite and lives in several places such as soil, sewage, freshwater, the walls of buildings and on the surface of monuments especially in polluted areas where the air contains high levels of nitrogen compounds.

<i>Nitrosomonas</i> Genus of bacteria

Nitrosomonas is a genus of Gram-negative bacteria, belonging to the Betaproteobacteria. It is one of the five genera of ammonia-oxidizing bacteria and, as an obligate chemolithoautotroph, uses ammonia as an energy source and carbon dioxide as a carbon source in presence of oxygen. Nitrosomonas are important in the global biogeochemical nitrogen cycle, since they increase the bioavailability of nitrogen to plants and in the denitrification, which is important for the release of nitrous oxide, a powerful greenhouse gas. This microbe is photophobic, and usually generate a biofilm matrix, or form clumps with other microbes, to avoid light. Nitrosomonas can be divided into six lineages: the first one includes the species Nitrosomonas europea, Nitrosomonas eutropha, Nitrosomonas halophila, and Nitrosomonas mobilis. The second lineage presents the species Nitrosomonas communis, N. sp. I and N. sp. II, meanwhile the third lineage includes only Nitrosomonas nitrosa. The fourth lineage includes the species Nitrosomonas ureae and Nitrosomonas oligotropha and the fifth and sixth lineages include the species Nitrosomonas marina, N. sp. III, Nitrosomonas estuarii and Nitrosomonas cryotolerans.

<span class="mw-page-title-main">Nitroso</span> Class of functional groups with a –N=O group attached

In organic chemistry, nitroso refers to a functional group in which the nitric oxide group is attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds, S-nitroso compounds, N-nitroso compounds, and O-nitroso compounds.

Nitrite reductase refers to any of several classes of enzymes that catalyze the reduction of nitrite. There are two classes of NIR's. A multi haem enzyme reduces NO2 to a variety of products. Copper containing enzymes carry out a single electron transfer to produce nitric oxide.

Nitrifying bacteria are chemolithotrophic organisms that include species of genera such as Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina, Nitrospira and Nitrococcus. These bacteria get their energy from the oxidation of inorganic nitrogen compounds. Types include ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). Many species of nitrifying bacteria have complex internal membrane systems that are the location for key enzymes in nitrification: ammonia monooxygenase, hydroxylamine oxidoreductase, and nitrite oxidoreductase.

<span class="mw-page-title-main">Camphor 5-monooxygenase</span>

In enzymology, a camphor 5-monooxygenase (EC 1.14.15.1) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Nitric oxide dioxygenase</span>

Nitric oxide dioxygenase (EC 1.14.12.17) is an enzyme that catalyzes the conversion of nitric oxide (NO) to nitrate (NO
3
) . The net reaction for the reaction catalyzed by nitric oxide dioxygenase is shown below:

In enzymology, an ethylbenzene hydroxylase (EC 1.17.99.2) is an enzyme that catalyzes the chemical reaction

In enzymology, a lignin peroxidase (EC 1.11.1.14) is an enzyme that catalyzes the chemical reaction

In enzymology, a manganese peroxidase (EC 1.11.1.13) is an enzyme that catalyzes the chemical reaction

In enzymology, a ferredoxin—nitrate reductase (EC 1.7.7.2) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Nitrite reductase (NO-forming)</span> Class of enzymes

In enzymology, a nitrite reductase (NO-forming) (EC 1.7.2.1) is an enzyme that catalyzes the chemical reaction

Nitric oxide reductase (cytochrome c) (EC 1.7.2.5) is an enzyme with systematic name nitrous oxide:ferricytochrome-c oxidoreductase. This enzyme catalyses the following chemical reaction

Hydroxylamine dehydrogenase (EC 1.7.2.6, HAO (ambiguous)) is an enzyme with systematic name hydroxylamine:ferricytochrome-c oxidoreductase. This enzyme catalyses the following chemical reaction

Nitrite dismutase (EC 1.7.6.1, Prolixin S, Nitrophorin 7) is an enzyme with systematic name nitrite:nitrite oxidoreductase. This enzyme catalyses the following chemical reaction

Ammonia monooxygenase (EC 1.14.99.39, AMO) is an enzyme, which catalyses the following chemical reaction

<span class="mw-page-title-main">Transition metal nitrite complex</span> Chemical complexes containing one or more –NO₂ ligands

In organometallic chemistry, transition metal complexes of nitrite describes families of coordination complexes containing one or more nitrite ligands. Although the synthetic derivatives are only of scholarly interest, metal-nitrite complexes occur in several enzymes that participate in the nitrogen cycle.

References

  1. 1 2 Caranto, Jonathan D.; Lancaster, Kyle M. (2017-07-17). "Nitric oxide is an obligate bacterial nitrification intermediate produced by hydroxylamine oxidoreductase". Proceedings of the National Academy of Sciences. 114 (31): 8217–8222. doi: 10.1073/pnas.1704504114 . ISSN   0027-8424. PMC   5547625 . PMID   28716929.
  2. Cedervall, Peder; Hooper, Alan B.; Wilmot, Carrie M. (2013-09-10). "Structural Studies of Hydroxylamine Oxidoreductase Reveal a Unique Heme Cofactor and a Previously Unidentified Interaction Partner". Biochemistry. 52 (36): 6211–6218. doi:10.1021/bi400960w. ISSN   0006-2960. PMID   23952581.
  3. Igarashi, N.; Moriyama, H.; Fujiwara, T.; Fukumori, Y.; Tanaka, N. (April 1997). "The 2.8 A structure of hydroxylamine oxidoreductase from a nitrifying chemoautotrophic bacterium, Nitrosomonas europaea". Nature Structural Biology. 4 (4): 276–284. doi:10.1038/nsb0497-276. ISSN   1072-8368. PMID   9095195. S2CID   1028628.
  4. Hendrich, Michael P.; Logan, Michael; Andersson, Kristoffer K.; Arciero, Dave M.; Lipscomb, John D.; Hooper, Alan B. (1994-12-01). "The Active Site of Hydroxylamine Oxidoreductase from Nitrosomonas: Evidence for a New Metal Cluster in Enzymes". Journal of the American Chemical Society. 116 (26): 11961–11968. doi:10.1021/ja00105a041. ISSN   0002-7863.
  5. Montzka, S. A.; Dlugokencky, E. J.; Butler, J. H. (2011). "Non-CO2 greenhouse gases and climate change". Nature. 476 (7358): 43–50. doi:10.1038/nature10322. PMID   21814274. S2CID   205225911.