scholarly journals Nature's nitrite-to-ammonia expressway, with no stop at dinitrogen

2021 ◽  
Author(s):  
Peter M. H. Kroneck
Keyword(s):  
Electron Transfer ◽  
Nitrite Reductase ◽  
Cytoplasmic Membrane ◽  
Nitrogen Loss ◽  
Nitrogen Retention ◽  
Significant Loss ◽  
X Ray Crystallography ◽  
Major Interest ◽  
Functional Features ◽  
Extracellular Side

Abstract Since the characterization of cytochrome c552 as a multiheme nitrite reductase, research on this enzyme has gained major interest. Today, it is known as pentaheme cytochrome c nitrite reductase (NrfA). Part of the NH4+ produced from NO2− is released as NH3 leading to nitrogen loss, similar to denitrification which generates NO, N2O, and N2. NH4+ can also be used for assimilatory purposes, thus NrfA contributes to nitrogen retention. It catalyses the six-electron reduction of NO2− to NH4+, hosting four His/His ligated c-type hemes for electron transfer and one structurally differentiated active site heme. Catalysis occurs at the distal side of a Fe(III) heme c proximally coordinated by lysine of a unique CXXCK motif (Sulfurospirillum deleyianum, Wolinella succinogenes) or, presumably, by the canonical histidine in Campylobacter jejeuni. Replacement of Lys by His in NrfA of W. succinogenes led to a significant loss of enzyme activity. NrfA forms homodimers as shown by high resolution X-ray crystallography, and there exist at least two distinct electron transfer systems to the enzyme. In γ-proteobacteria (Escherichia coli) NrfA is linked to the menaquinol pool in the cytoplasmic membrane through a pentaheme electron carrier (NrfB), in δ- and ε-proteobacteria (S. deleyianum, W. succinogenes), the NrfA dimer interacts with a tetraheme cytochrome c (NrfH). Both form a membrane-associated respiratory complex on the extracellular side of the cytoplasmic membrane to optimize electron transfer efficiency. This minireview traces important steps in understanding the nature of pentaheme cytochrome c nitrite reductases, and discusses their structural and functional features. Graphical abstract

scholarly journals A three-domain copper-nitrite reductase with a unique sensing loop

IUCrJ ◽  
2019 ◽  
Vol 6 (2) ◽  
pp. 248-258 ◽  
Author(s):  
Diederik Johannes Opperman ◽  
Daniel Horacio Murgida ◽  
Sergio Daniel Dalosto ◽  
Carlos Dante Brondino ◽  
Felix Martín Ferroni
Keyword(s):  
Nitrite Reductase ◽  
Thermophilic Bacterium ◽  
Nitrite Reduction ◽  
Molecular Surface ◽  
Paramagnetic Resonance ◽  
X Ray Crystallography ◽  
Gaseous Products ◽  
C Terminus ◽  
Functional Features

Dissimilatory nitrite reductases are key enzymes in the denitrification pathway, reducing nitrite and leading to the production of gaseous products (NO, N2O and N2). The reaction is catalysed either by a Cu-containing nitrite reductase (NirK) or by a cytochromecd1nitrite reductase (NirS), as the simultaneous presence of the two enzymes has never been detected in the same microorganism. The thermophilic bacteriumThermus scotoductusSA-01 is an exception to this rule, harbouring both genes within a denitrification cluster, which encodes for an atypical NirK. The crystal structure ofTsNirK has been determined at 1.63 Å resolution.TsNirK is a homotrimer with subunits of 451 residues that contain three copper atoms each. The N-terminal region possesses a type 2 Cu (T2Cu) and a type 1 Cu (T1CuN) while the C-terminus contains an extra type 1 Cu (T1CuC) bound within a cupredoxin motif. T1CuNshows an unusual Cu atom coordination (His2–Cys–Gln) compared with T1Cu observed in NirKs reported so far (His2–Cys–Met). T1CuCis buried at ∼5 Å from the molecular surface and located ∼14.1 Å away from T1CuN; T1CuNand T2Cu are ∼12.6 Å apart. All these distances are compatible with an electron-transfer process T1CuC→ T1CuN→ T2Cu. T1CuNand T2Cu are connected by a typical Cys–His bridge and an unexpected sensing loop which harbours a SerCATresidue close to T2Cu, suggesting an alternative nitrite-reduction mechanism in these enzymes. Biophysicochemical and functional features ofTsNirK are discussed on the basis of X-ray crystallography, electron paramagnetic resonance, resonance Raman and kinetic experiments.

Utilization of grass-silage nitrogen by growing sheep

1983 ◽  
Vol 100 (1) ◽  
pp. 43-62 ◽  
Author(s):  
Elisabeth Grenet
Keyword(s):  
Organic Matter ◽  
Formic Acid ◽  
Nitrogen Balance ◽  
Crude Protein ◽  
Nitrogen Loss ◽  
Nitrogen Retention ◽  
Protein Digestibility ◽  
Water Soluble ◽  
Nitrogen Intake ◽  
Green Fodder

SUMMARYThe digestibility, the voluntary intake and the nitrogen balance of 108 diets corresponding to 94 silages prepared from 20 fresh crops were measured in growing sheep. Series of silages were made from the same fresh forage. Each series included two controls: a direct-cut silage without additive and a direct-cut silage with formic acid, with a variable number of experimental silages with different additives.Rumen ammonia concentration, measured on rumen-fistulated sheep, decreased when an additive was used. It increased with nitrogen intake and was inversely related to the organic-matter digestibility and the crude-fibre digestibility. It varied with the silage composition.The crude-protein digestibility of direct-cut silages without additives was similar to or slightly higher than the crude-protein digestibility of the fresh crops. The addition of formic acid depressed the digestibility, but the addition of formaldehyde decreased it even more. The urinary nitrogen loss was higher for silages without additive than for the fresh crops and was decreased by the addition of formic acid. The addition of formaldehyde to formic acid had an additive effect.Retained nitrogen was lower in silages without additives (12% of nitrogen intake) than in parent crops (15·7%). It increased when formic acid (15·8%) was added. The addition of formaldehyde at a low rate (1·5 l/t green fodder) to the formic acid did not increase the nitrogen retention whether expressed in g/day or as percentage of nitrogen intake, but the addition of formaldehyde at a high rate (3·5 l/t green fodder) to formic acid decreased nitrogen retention. The other additives based on cereals or whey did not improve the nitrogen balance compared with formic acid. Nitrogen retention differed according to plant species.Retained nitrogen increased with digestible organic-matter intake and nitrogen intake. It increased with the silage water-soluble carbohydrate content. The higher the silage fermentation product content (ammonia, lactic acid, propionic acid), the lower the retained nitrogen. It appears that the nitrogen value of silages can be high provided that the silages are well preserved and that excessive protein breakdown is avoided.

New development of photoinduced electron-transfer catalytic systems

2007 ◽  
Vol 79 (6) ◽  
pp. 981-991 ◽  
Author(s):  
Shunichi Fukuzumi
Keyword(s):  
Electron Transfer ◽  
Organic Solar Cells ◽  
Charge Separation ◽  
Energy Charge ◽  
High Energy ◽  
Significant Loss ◽  
Catalytic Systems ◽  
Molecular Electron ◽  
New Development ◽  
Donor Acceptor

As an alternative to conventional charge-separation functional molecular models based on multi-step long-range electron transfer (ET) within redox cascades, simple donor-acceptor dyads have been developed to attain a long-lived and high-energy charge-separated (CS) state without significant loss of excitation energy. In particular, a simple molecular electron donor-acceptor dyad, 9-mesityl-10-methylacridinium ion (Acr+-Mes), is capable of fast charge separation but extremely slow charge recombination. Such a simple molecular dyad has significant advantages with regard to synthetic feasibility, providing a variety of applications for photoinduced ET catalytic systems, including efficient photocatalytic systems for the solar energy conversion and construction of organic solar cells.

QM/MM MD simulations reveal an asynchronous PCET mechanism for nitrite reduction by copper nitrite reductase

2020 ◽  
Vol 22 (36) ◽  
pp. 20922-20928
Author(s):  
Ronny Cheng ◽  
Chun Wu ◽  
Zexing Cao ◽  
Binju Wang
Keyword(s):  
Electron Transfer ◽  
Proton Transfer ◽  
Nitrite Reductase ◽  
Md Simulations ◽  
Nitrite Reduction ◽  
Proton Coupled Electron Transfer

The nitrite reduction in copper nitrite reductase is found to proceed through an asynchronous proton-coupled electron transfer (PCET) mechanism, with electron transfer from T1-Cu to T2-Cu preceding the proton transfer from Asp98 to nitrite.

Conformation of Pseudoazurin in the 152 kDa Electron Transfer Complex with Nitrite Reductase Determined by Paramagnetic NMR

2008 ◽  
Vol 375 (5) ◽  
pp. 1405-1415 ◽  
Author(s):  
Monica D. Vlasie ◽  
Rubén Fernández-Busnadiego ◽  
Miguel Prudêncio ◽  
Marcellus Ubbink
Keyword(s):  
Electron Transfer ◽  
Nitrite Reductase ◽  
Paramagnetic Nmr ◽  
Electron Transfer Complex
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