NO Reduction (no + reduction)

Distribution by Scientific Domains

Selected Abstracts

Kinetics of electron transfer from NADH to the Escherichia coli nitric oxide reductase flavorubredoxin

FEBS JOURNAL, Issue 3 2007
Joo B. Vicente
Escherichia coli flavorubredoxin (FlRd) belongs to the family of flavodiiron proteins (FDPs), microbial enzymes that are expressed to scavenge nitric oxide (NO) under anaerobic conditions. To degrade NO, FlRd has to be reduced by NADH via the FAD-binding protein flavorubredoxin reductase, thus the kinetics of electron transfer along this pathway was investigated by stopped-flow absorption spectroscopy. We found that NADH, but not NADPH, quickly reduces the FlRd-reductase (k = 5.5 2.2 106 m,1s,1 at 5 C), with a limiting rate of 255 17 s,1. The reductase in turn quickly reduces the rubredoxin (Rd) center of FlRd, as assessed at 5 C working with the native FlRd enzyme (k = 2.4 0.1 106 m,1s,1) and with its isolated Rd-domain (k , 1 107 m,1s,1); in both cases the reaction was found to be dependent on pH and ionic strength. In FlRd the fast reduction of the Rd center occurs synchronously with the formation of flavin mononucleotide semiquinone. Our data provide evidence that (a) FlRd-reductase rapidly shuttles electrons between NADH and FlRd, a prerequisite for NO reduction in this detoxification pathway, and (b) the electron accepting site in FlRd, the Rd center, is in very fast redox equilibrium with the flavin mononucleotide. [source]

Effect of CaO on NH3 + NO + O2 reaction system in the absence and presence of high concentration CO2

Tianjin Li
Abstract The effect of CaO on the NH3 + NO + O2 reaction system at 650,850 C was investigated. High CO2 concentration was added to investigate the effect of CaCO3 on this reaction system also. Experimental results showed that CaO had a strong catalytic effect on NH3 decomposition, NH3 oxidation by O2 to NO, and NO reduction by NH3 in the absence of O2. The overall effect of CaO on the NO + NH3 + O2 reaction was to enhance NH3 oxidation by O2 to produce more NO. A small amount of NO2 and no N2O was detected in the outlet gas stream over CaO in the NH3 + NO + O2 reaction. NO2 formation decreased with temperature increase. NO2 formation in the NH3 + NO + O2 reaction over CaO was attributed to the oxidization of NH3 and NO by O2. The performance of CaCO3 was different from CaO. NH3 decomposition was promoted, but NH3 oxidation to NO was inhibited after CaO was converted to CaCO3. No catalytic activity for NO reduction was detected in NO + NH3 reaction over CaCO3, but strong activity for NH3 decomposition was observed. NO and NH3 outlet concentration over CaCO3 in the NH3 + NO + O2 reaction was lower and higher, respectively, than that of CaO, which was mainly due to the difference of CaO and CaCO3 for NH3 oxidation. NO2 formation was inhibited, but N2O was observed over CaCO3. N2O formation increased with temperature increase at 650,750 C, and then decreased at 750,850 C. Copyright 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Design of a Functional Nitric Oxide Reductase within a Myoglobin Scaffold

CHEMBIOCHEM, Issue 8 2010
Valentin Khler Dr.
One site fits all: Yi Lu and co-workers have reported the conversion of sperm-whale myoglobin into a functional nitric oxide reductase. For this purpose, they designed a second metal binding site in the wild-type holo-protein and demonstrated NO reduction with the structurally characterized model, making thereby a significant contribution to the rapidly developing field of artificial metalloenzymes. [source]

Nanostructured Praseodymium Oxide: Correlation Between Phase Transitions and Catalytic Activity

CHEMCATCHEM, Issue 6 2010
Patrick Sonstrm
Abstract Praseodymia gives rise to a rich phase diagram with a large number of phases between the limiting stoichiometries Pr2O3 and PrO2 that differ only slightly in oxygen content (PrnO2n,2). This chemical and crystallographic variability allows the system to release or incorporate lattice oxygen easily at sufficiently high temperatures and thus renders the material interesting as a catalyst for redox reactions according to a Mars,van,Krevelen mechanism. Nanostructured praseodymia samples are investigated in this study with respect to their catalytic properties, focusing on methane oxidation and selective NO reduction by CO and CH4. To correlate catalytic activity and crystallographic changes, complementary high-temperature X-ray diffraction measurements have been carried out. The determined temperatures of transitions between different oxide phases agree well with peaks in the temperature-programmed reduction measurements, confirming the direct connection between the availability of lattice oxygen and crystallographic transformations. The catalytic activity for methane oxidation and NO reduction sets in at 450,500,C, at which temperature the starting material,mainly Pr6O11,transforms into the next oxygen-depleted phase Pr7O12. With respect to NO reduction, the results show that it is possible to employ both methane and carbon monoxide as reducing agents in the absence of oxygen, in agreement with a Mars,van,Krevelen mechanism. Nevertheless, the use of CO instead of CH4 offers considerable advantages, as no deactivation due to carbon residues takes place in this case. Whereas, in an excess of oxygen, NO reduction is inhibited independently of the reducing agent, it is shown that NO reduction can proceed if the O2 concentration remains below a critical concentration. [source]

Using Acetylene for Selective Catalytic Reduction of NO in Excess Oxygen

Shan-Shan Yu
Abstract Acetylene as a reducing agent for selective catalytic reduction of NO (C2H2 -SCR) was investigated over a series of metal exchanged HY catalysts, in the reaction system of 0.16% NO, 0.08% C2H2, and 9.95% O2 (volume percent) in He. 75% of NO conversion to N2 with hydrocarbon efficiency about 1.5 was achieved over a Ce-HY catalyst around 300 C. The NO removal level was comparable with that of selective catalytic reduction of NOx by C3H6 reported in literatures, although only one third of the reducing agent in carbon moles was used in the C2H2 -SCR of NO. The protons in zeolite were crucial to the C2H2 -SCR of NO, and the performance of HY in the reaction was significantly promoted by cerium incorporation into the zeolite. NO2 was proposed to be the intermediate of NO reduction to N2, and the oxidation of NO to NO2 was rate-determining step of the C2H2 -SCR of NO over Ce-HY. The suggestion was well supported by the results of the NO oxidation with O2, and the C2H2 consumption under the conditions in the presence or absence of NO. [source]