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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 (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 ( N O 2 ) under aerobic conditions. Although we observe N O 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 N O 2 results when nitric oxide (NO) dissociates from the {FeNO} 6 intermediate and reacts with dioxygen. Thus, N O 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.

Authors:
 [1];  [1];  [2]
  1. Cornell Univ., Ithaca, NY (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. Cornell Univ., Ithaca, NY (United States)
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 Volume: 113; Journal Issue: 51; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
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. doi:10.1073/pnas.1611051113.
Caranto, Jonathan D., Vilbert, Avery C., and Lancaster, Kyle M. Wed . "Nitrosomonas europaea cytochrome P460 is a direct link between nitrification and nitrous oxide emission". United States. doi: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 (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 ( N O 2 − ) under aerobic conditions. Although we observe N O 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 N O 2 − results when nitric oxide (NO) dissociates from the {FeNO} 6 intermediate and reacts with dioxygen. Thus, N O 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.},
doi = {10.1073/pnas.1611051113},
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 = {2016},
month = {11}
}

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

Citation Metrics:
Cited by: 12 works
Citation information provided by
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