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

Abstract

Ammonia oxidizing bacteria (AOB) are major contributors to the emission of nitrous oxide (N2O). It has been proposed that N2O is produced by reduction of NO. Here, we report that the enzyme cytochrome (cyt) P460 from the AOB Nitrosomonas europaea converts hydroxylamine (NH2OH) quantitatively to N2O under anaerobic conditions. Previous literature reported that this enzyme oxidizes NH2OH to nitrite (NO2) under aerobic conditions. Although we observe NO2 formation under aerobic conditions, its concentration is not stoichiometric with the NH2OH concentration. By contrast, under anaerobic conditions, the enzyme uses 4 oxidizing equivalents (eq) to convert 2 eq of NH2OH to N2O. Enzyme kinetics coupled to UV/visible absorption and electron paramagnetic resonance (EPR) spectroscopies support a mechanism in which an FeIII–NH2OH adduct of cyt P460 is oxidized to an {FeNO}6 unit. This species subsequently undergoes nucleophilic attack by a second equivalent of NH2OH, forming the N–N bond of N2O during a bimolecular, rate-determining step. We propose that NO2 results when nitric oxide (NO) dissociates from the {FeNO}6 intermediate and reacts with dioxygen. Furthermore, NO2 is not a direct product of cyt P460 activity. We hypothesize that the cyt P460 oxidation of NH2OH contributes to NO and N2O emissions from nitrifying microorganisms.

Authors:
 [1];  [1];  [1]
  1. Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853
Publication Date:
Research Org.:
Cornell Univ., Ithaca, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1332766
Alternate Identifier(s):
OSTI ID: 1464941
Grant/Contract Number:  
SC0013997
Resource Type:
Journal Article: Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 113 Journal Issue: 51; Journal ID: ISSN 0027-8424
Publisher:
Proceedings of the National Academy of Sciences
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; nitric oxide; nitrification; nitrous oxide; enzymology; bioinorganic chemistry

Citation Formats

Caranto, Jonathan D., Vilbert, Avery C., and Lancaster, Kyle M. Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission. United States: N. p., 2016. Web. doi:10.1073/pnas.1611051113.
Caranto, Jonathan D., Vilbert, Avery C., & Lancaster, Kyle M. Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission. United States. https://doi.org/10.1073/pnas.1611051113
Caranto, Jonathan D., Vilbert, Avery C., and Lancaster, Kyle M. 2016. "Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission". United States. https://doi.org/10.1073/pnas.1611051113.
@article{osti_1332766,
title = {Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission},
author = {Caranto, Jonathan D. and Vilbert, Avery C. and Lancaster, Kyle M.},
abstractNote = {Ammonia oxidizing bacteria (AOB) are major contributors to the emission of nitrous oxide (N2O). It has been proposed that N2O is produced by reduction of NO. Here, we report that the enzyme cytochrome (cyt) P460 from the AOB Nitrosomonas europaea converts hydroxylamine (NH2OH) quantitatively to N2O under anaerobic conditions. Previous literature reported that this enzyme oxidizes NH2OH to nitrite (NO–2) under aerobic conditions. Although we observe NO–2 formation under aerobic conditions, its concentration is not stoichiometric with the NH2OH concentration. By contrast, under anaerobic conditions, the enzyme uses 4 oxidizing equivalents (eq) to convert 2 eq of NH2OH to N2O. Enzyme kinetics coupled to UV/visible absorption and electron paramagnetic resonance (EPR) spectroscopies support a mechanism in which an FeIII–NH2OH adduct of cyt P460 is oxidized to an {FeNO}6 unit. This species subsequently undergoes nucleophilic attack by a second equivalent of NH2OH, forming the N–N bond of N2O 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. Furthermore, NO–2 is not a direct product of cyt P460 activity. We hypothesize that the cyt P460 oxidation of NH2OH contributes to NO and N2O emissions from nitrifying microorganisms.},
doi = {10.1073/pnas.1611051113},
url = {https://www.osti.gov/biblio/1332766}, journal = {Proceedings of the National Academy of Sciences of the United States of America},
issn = {0027-8424},
number = 51,
volume = 113,
place = {United States},
year = {Wed Nov 16 00:00:00 EST 2016},
month = {Wed Nov 16 00:00:00 EST 2016}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at https://doi.org/10.1073/pnas.1611051113

Citation Metrics:
Cited by: 125 works
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