Environmental Engineering Reference
In-Depth Information
Table 1 Selected enzymes and enzyme complexes involved in respiratory ammonia production or consumption. Modified from [
24
].
Enzyme designation
a
Selected model organism(s)
b
Physiological function
Redox partner
AMMONIA-PRODUCING ENZYMES
1. NITROGENASE
1.1 (NifDK)
2
complex, the heterotetra-
meric MoFe protein (containing the
FeMo cofactor, a [Mo:7Fe:9S:C]:
homocitrate moiety)
Cytoplasmic nitrogen reduction to
ammonia
ATP-hydrolyzing NifH
homodimer (Fe protein)
Azotobacter vinelandii
(
ʳ
),
Klebsiella
pneumoniae
(
ʳ
)
2. NITRITE REDUCTASES
2.1 NrfHA complex (NrfA: 5 heme
c
; one
CX
2
CK motif; NrfH: four heme
c
;
Dimers of NrfHA
2
assembly in
crystal structure)
Periplasmic nitrite ammonification as
well as reduction of NO and NH
2
OH to
ammonia
Quinol (oxidized
by NrfH)
Wolinella succinogenes
(
ʵ
),
Desulfovibrio vulgaris
(
),
Desulfovibrio desulfuricans
(
ʴ
ʴ
),
Bacillus
vireti
(Firmicutes)
2.2 NrfA (5 heme
c
; five CH
2
CH motifs)
ditto
ditto
Campylobacter jejuni
(
ʵ
)
2.3 NrfA (5 heme
c
; one CX
2
CK motif)
ditto
Tetraheme cytochrome
c
quinol dehydrogenase
CymA
Shewanella oneidensis
(
ʳ
)
2.4 NrfA (5 heme
c
; one CX
2
CK motif;
dimeric)
ditto
Pentaheme cytochrome
c
NrfB
Escherichia coli
(
ʳ
);
Neisseria
gonorrhoeae
2.5 Otr (8 heme
c
)
Not known. Otr reduces nitrite and
hydroxylamine to ammonia. It also
interconverts tetrathionate and
thiosulfate.
Not known
Shewanella oneidensis
(
ʳ
),
Geobacter
species (
ʴ
)
2.6 Onr (8 heme
c
; hexameric)
Not known. Onr reduces nitrite and
hydroxylamine to ammonia. It also
reduces sulfite and hydrogen peroxide.
Not known
Thioalkalivibrio nitratireducens
(
ʳ
),
Thioalkalivibrio paradoxus
(
ʳ
),
Geobacter
species (
ʴ
)
2.7
ʵ
Hao (8 heme
c
)
Most likely nitrite reduction.
The reaction product has not been
reported.
Presumably a cyto-
chrome
c
of the
NapC/NrfH family
Campylobacter concisus
,
Campylobacter
curvus
,
Campylobacter fetus
,
Nautilia
profundicola
(all
ʵ
)
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