scholarly journals Diversity and evolution of nitric oxide reduction

2021 ◽  
Author(s):  
James Hemp ◽  
Ranjani Murali ◽  
Laura A Pace ◽  
Robert A Sanford ◽  
Roland Hatzenpichler ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Active Site ◽  
Phylogenetic Analyses ◽  
Essential Element ◽  
Nitric Oxide Reductase ◽  
Oxide Reduction ◽  
Rhodothermus Marinus ◽  
Fixed Nitrogen ◽  
Proton Channels ◽  
Nitric Oxide Reduction

Nitrogen is an essential element for life, with the availability of fixed nitrogen limiting productivity in many ecosystems. The return of oxidized nitrogen species to the atmospheric N2 pool is predominately catalyzed by microbial denitrification (NO3- → NO2- → NO → N2O → N2). Incomplete denitrification can produce N2O as a terminal product, leading to an increase in atmospheric N2O, a potent greenhouse and ozone depleting gas2. The production of N2O is catalyzed by nitric oxide reductase (NOR) members of the heme-copper oxidoreductase (HCO) superfamily3. Here we propose that a number of uncharacterized HCO families perform nitric oxide reduction and demonstrate that an enzyme from Rhodothermus marinus, belonging to one of these families does perform nitric oxide reduction. These families have novel active-site structures and several have conserved proton channels, suggesting that they might be able to couple nitric oxide reduction to energy conservation. They also exhibit broad phylogenetic and environmental distributions, expanding the diversity of microbes that can perform denitrification. Phylogenetic analyses of the HCO superfamily demonstrate that nitric oxide reductases evolved multiple times independently from oxygen reductases, suggesting that complete denitrification evolved after aerobic respiration.

Kinetic and thermodynamic resolution of the interactions between sulfite and the pentahaem cytochrome NrfA from Escherichia coli

2010 ◽  
Vol 431 (1) ◽  
pp. 73-80 ◽  
Author(s):  
Gemma L. Kemp ◽  
Thomas A. Clarke ◽  
Sophie J. Marritt ◽  
Colin Lockwood ◽  
Susannah R. Poock ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Escherichia Coli ◽  
Active Site ◽  
Dissociation Constants ◽  
Cellular Activity ◽  
Nitric Oxide Reductase ◽  
Wide Range ◽  
Nitric Oxide Reduction ◽  
Nitric Oxide Detoxification ◽  
Kinetic And Thermodynamic Studies

NrfA is a pentahaem cytochrome present in a wide-range of γ-, δ- and ε-proteobacteria. Its nitrite and nitric oxide reductase activities have been studied extensively and contribute to respiratory nitrite ammonification and nitric oxide detoxification respectively. Sulfite is a third substrate for NrfA that may be encountered in the micro-oxic environments where nrfA is expressed. Consequently, we have performed quantitative kinetic and thermodynamic studies of the interactions between sulfite and Escherichia coli NrfA to provide a biochemical framework from which to consider their possible cellular consequences. A combination of voltammetric, spectroscopic and crystallographic analyses define dissociation constants for sulfite binding to NrfA in oxidized (~54 μM), semi-reduced (~145 μM) and reduced (~180 μM) states that are comparable with each other, and the Km (~70 μM) for sulfite reduction at pH 7. Under comparable conditions Km values of ~22 and ~300 μM describe nitrite and nitric oxide reduction respectively, whereas the affinities of nitrate and thiocyanate for NrfA fall more than 50-fold on enzyme reduction. These results are discussed in terms of the nature of sulfite co-ordination within the active site of NrfA and their implications for the cellular activity of NrfA.

Molecular mechanism of nitric oxide reduction catalyzed by fungal nitric oxide reductase

2002 ◽  
Vol 1233 ◽  
pp. 59-62 ◽  
Author(s):  
Eiji Obayashi ◽  
Hideaki Shimizu ◽  
Sam-Yong Park ◽  
Hiro Nakamura ◽  
Satoshi Takahashi ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Molecular Mechanism ◽  
Nitric Oxide Reductase ◽  
Oxide Reduction ◽  
Nitric Oxide Reduction

Ultra-Low Amounts of Palladium (0.005-0.05 Wt% Pd) Supported on Titania: Remarkable Low-Temperature Activity for NO Reduction with CO and Structure-Function Property Relationships in Methane Oxidation

2020 ◽  
Author(s):  
Konstantin Khivantsev ◽  
Libor Kovarik ◽  
Nicholas R. Jaegers ◽  
János Szanyi ◽  
Yong Wang
Keyword(s):  
Nitric Oxide ◽  
Carbon Monoxide ◽  
Methane Oxidation ◽  
Steam Reforming ◽  
Methane Steam Reforming ◽  
Oxide Reduction ◽  
Water Steam ◽  
Methane Steam ◽  
Anatase Titania ◽  
Nitric Oxide Reduction

<p>Atomically dispersed Pd +2 cations with ultra-dilute loading of palladium (0.005-0.05 wt%) were anchored on anatase titania and characterized with FTIR, microscopy and catalytic tests. CO infrared adsorption produces a sharp, narrow mono-carbonyl Pd(II)-CO band at ~2,130 cm<sup>-1</sup> indicating formation of highly uniform and stable Pd+2 ions on anatase titania. The 0.05 wt% Pd/TiO<sub>2</sub> sample was evaluated for methane combustion under dry and wet (industrially relevant) conditions in the presence and absence of carbon monoxide. Notably, we find the isolated palladium atoms respond dynamically upon oxygen concentration modulation (switching-on and switching off). When oxygen is removed from the wet methane stream, palladium ions are reduced to metallic state by methane and catalyze methane steam reforming instead of complete methane oxidation. Re-admission of oxygen restores Pd<sup>+2</sup> cations and switches off methane steam reforming activity. Moreover, 0.05 wt% Pd/TiO<sub>2</sub> is a competent CO oxidation catalyst in the presence of water steam with 90% CO conversion and TOF ~ 4,000 hr<sup>-1</sup> at 260 ⁰C. </p><p>More importantly, we find that diluting 0.05 wt% Pd/titania sample with titania to ultra-low 0.005 wt% palladium loading produces a remarkably active material for nitric oxide reduction with carbon monoxide under industrially relevant conditions with >90% conversion of nitric oxide at 180 ⁰C (~460 ppm NO and 150 L/g*hr flow rate in the presence of >2% water steam) and TOF ~6,000 hr<sup>-1</sup>. Pd thus outperforms state-of-the-art rhodium containing catalysts with (15-20 times higher rhodium loading; rhodium is ~ 3 times more expensive than palladium). Furthermore, palladium catalysts are more selective towards nitrogen and produce significantly less ammonia relative to the more traditional rhodium catalysts due to lower Pd amount nd lower water-gas-shift activity. Our study is the first example of utilizing ultra-low (0.05 wt% and less) noble metal (Pd) amounts to produce heterogeneous catalysts with extraordinary activity for nitric oxide reduction. This opens up a pathway to study other Pd, Pt and Rh containing materials with ultra-low loadings of expensive noble metals dispersed on titania or titania-coated oxides for industrially relevant nitric oxide abatement.</p>

Reaction of Carbon Monoxide with the Reduced Active Site of Bacterial Nitric Oxide Reductase†

Biochemistry ◽  
2001 ◽  
Vol 40 (44) ◽  
pp. 13361-13369 ◽  
Author(s):  
Janneke H. M. Hendriks ◽  
Louise Prior ◽  
Adam R. Baker ◽  
Andrew J. Thomson ◽  
Matti Saraste ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Carbon Monoxide ◽  
Active Site ◽  
Nitric Oxide Reductase
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