Environmental Engineering Reference
In-Depth Information
intact [4Cu:2S] Cu
Z
site, and why this doubly-sulfurated form I of N
2
OR can
readily be isolated from bacteria that have actively turned over N
2
O during
denitrificatory growth, using the exact protein that was isolated after harvesting
of the biomass. It therefore is imminent to address the issue of assembly and
maturation of the Cu
Z
center and generate structural pictures - ideally verified by
single-crystal spectroscopy - that align the different states of the enzyme with the
spectroscopy data at the highest resolution possible.
Moreover, it will also be essential to determine whether a full-reduced, all-Cu(I)
state of Cu
Z
can be generated
in vivo
and which mechanisms might be in place to
deliver the required low-potential electrons to a periplasmic enzyme. No such
process was observed to date and it seems quite difficult to envision indeed, but
one of the great aspects of science surely is that very few things, really, seem to be
impossible in nature. Astounding progress has been made in recent years, and the
field seems all set to eventually provide some of those famed 'final answers'
regarding the biological reduction of nitrous oxide.
Abbreviations and Definitions
aa
amino acid
anammox
anaerobic ammonia oxidation
adenosine 5
0
-triphosphate
ATP
CFC
chlorofluorocarbon
DNRA
dissimilatory nitrate reduction to ammonia
en
ethylenediamine (
¼
1,2-diaminoethane)
EPR
electron paramagnetic resonance
ENDOR
electron nuclear double resonance
EXAFS
extended X-ray absorption fine structure
LMCT
ligand-to-metal charge transfer
LUMO
lowest unoccupied molecular orbital
NADPH
nicotinamide adenine dinucleotide phosphate (reduced)
NMR
nuclear magnetic resonance
N
2
OR
nitrous oxide reductase
NO
x
atmospheric nitrogen oxides (NO
x
¼
NO+ NO
2
)
orf
open reading frame
ppbv
parts per billion by volume
Tat
twin-arginine translocation
mol (substrate) · min
-1
·mg
-1
(protein))
U
unit of enzymatic activity (
ʼ
Acknowledgment The authors thank Peter Kroneck, Walter Zumft, J¨ rg Simon, Sofia Pauleta,
and Isabel Moura for stimulating discussions. This work was supported by Deutsche Forschungs-
gemeinschaft, Deutscher Akademischer Austauschdienst,
the BIOSS Centre for Biological
Signalling Studies, and the European Research Council.
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