Nitric oxide is an obligate bacterial nitrification intermediate produced by hydroxylamine oxidoreductase.
basic_science · Level V
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- Record sourced from PubMed, PMID 28716929.
- Also identified by DOI 10.1073/pnas.1704504114 and PMC identifier 5547625.
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Abstract
Ammonia (NH<sub>3</sub>)-oxidizing bacteria (AOB) emit substantial amounts of nitric oxide (NO) and nitrous oxide (N<sub>2</sub>O), both of which contribute to the harmful environmental side effects of large-scale agriculture. The currently accepted model for AOB metabolism involves NH<sub>3</sub> oxidation to nitrite (NO<sub>2</sub><sup>-</sup>) via a single obligate intermediate, hydroxylamine (NH<sub>2</sub>OH). Within this model, the multiheme enzyme hydroxylamine oxidoreductase (HAO) catalyzes the four-electron oxidation of NH<sub>2</sub>OH to NO<sub>2</sub><sup>-</sup> We provide evidence that HAO oxidizes NH<sub>2</sub>OH by only three electrons to NO under both anaerobic and aerobic conditions. NO<sub>2</sub><sup>-</sup> observed in HAO activity assays is a nonenzymatic product resulting from the oxidation of NO by O<sub>2</sub> under aerobic conditions. Our present study implies that aerobic NH<sub>3</sub> oxidation by AOB occurs via two obligate intermediates, NH<sub>2</sub>OH and NO, necessitating a mediator of the third enzymatic step.
Medical subject headings
- Bacterial Proteins
- Nitric Oxide
- Nitrosomonas europaea
- Oxidoreductases