Nitrite oxidoreductase (NOR or NXR) is an enzyme involved in
nitrification
''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 am ...
. It is the last step in the process of aerobic ammonia oxidation, which is carried out by two groups of
nitrifying bacteria 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 oxidat ...
: ammonia oxidizers such as ''
Nitrosospira'', ''
Nitrosomonas
''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 (NH3) as an energy source and carbon di ...
'' and ''
Nitrosococcus'' convert ammonia to nitrite, while nitrite oxidizers such as ''
Nitrobacter
''Nitrobacter'' is a genus comprising rod-shaped, gram-negative, and chemoautotrophic bacteria. The name ''Nitrobacter'' derives from the Latin neuter gender noun ''nitrum, nitri'', alkalis; the Ancient Greek noun βακτηρία'','' βακτ ...
'' and ''
Nitrospira
''Nitrospira'' (from Latin: nitro, meaning "nitrate" and Greek: spira, meaning "spiral") translate into “a nitrate spiral” is a genus of bacteria within the monophyletic clade of the Nitrospirota phylum. The first member of this genus was d ...
'' oxidize nitrite to nitrate.
The enzyme is bound to the inner cytoplasmic surface of the bacterial membrane and contains multiple subunits, iron-sulfur centers and a
molybdenum cofactor. The enzyme is relatively abundant, making up 10-30% of the total protein in these bacteria and forms densely packed structures on the membrane surface.
;Reaction
:
+ acceptor <=> + reduced\ acceptor
See also
*
Microbial metabolism
Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon) it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other ...
*
Ferredoxin—nitrite reductase involved in the
assimilation of nitrates by plants
References
External links
MetaCyc Pathway: nitrite oxidation
Oxidoreductases
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