A new role for nitric oxide in greenhouse gas formation | August 28, 2017 Issue - Vol. 95 Issue 34 | Chemical & Engineering News
Volume 95 Issue 34 | p. 10 | Concentrates
Issue Date: August 28, 2017

A new role for nitric oxide in greenhouse gas formation

Better understanding of nitrogen cycling from fertilizer runoff could help control emissions
Department: Science & Technology
News Channels: Environmental SCENE
Keywords: Greenhouse gases, Environment, Water, Agriculture, Nitrification, Ammonia, Nitrous oxide, Nitric oxide, Hydroxylamine, Oxidoreductase, Nitrosocyanin
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Cornell scientists have identified nitric oxide (NO) as an intermediate in nitrification; side reactions form nitrous oxide (N2O).
Reaction scheme showing conversion of ammonia to hydroxylamine, nitric oxide, and nitrite, with side reactions to nitrous oxide.
 
Cornell scientists have identified nitric oxide (NO) as an intermediate in nitrification; side reactions form nitrous oxide (N2O).

Fertilizer runoff from farmlands can create algae blooms that cause hypoxic dead zones in rivers, lakes, and oceans. But the runoff can also lead to the release of nitrous oxide (N2O), a greenhouse gas that can also destroy the ozone layer. In soils and during wastewater treatment, microbial enzymes convert fertilizer ammonia (NH3) into other nitrogen compounds through a process called nitrification. Nitric oxide (NO) is a key intermediate in the nitrification pathway rather than a by-product, as previously thought, reported Cornell University researchers at the ACS national meeting. Postdoc Jonathan D. Caranto and his adviser, Kyle Lancaster, studied nitrification in Nitrosomonas europaea, which is the dominant ammonia-oxidizing bacteria species in wastewater treatment plants. One enzyme converts NH3 to hydroxylamine (NH2OH). Previously, researchers thought that a second enzyme, hydroxylamine oxidoreductase (HAO), then oxidized NH2OH to NO2. Under anaerobic conditions, NO2 gets reduced to N2O, yielding some NO from incomplete catalysis. Instead, Caranto and Lancaster found that HAO converts NH2OH to NO (Proc. Natl. Acad. Sci.USA2017, DOI: 10.1073/pnas.1704504114). A third enzyme would then take NO to NO2. Depending on conditions, some NO could escape and undergo side reactions to form N2O. Meanwhile, the race is on to identify the enzyme that oxidizes NO to NO2.

 
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