Nitrite Reductases: A group of enzymes that oxidize diverse nitrogenous substances to yield nitrite. (Enzyme Nomenclature, 1992) EC 1.Nitrites: Salts of nitrous acid or compounds containing the group NO2-. The inorganic nitrites of the type MNO2 (where M=metal) are all insoluble, except the alkali nitrites. The organic nitrites may be isomeric, but not identical with the corresponding nitro compounds. (Grant & Hackh's Chemical Dictionary, 5th ed)Nitrite Reductase (NAD(P)H): An enzyme found primarily in BACTERIA and FUNGI that catalyzes the oxidation of ammonium hydroxide to nitrite. It is an iron-sulfur HEME; FLAVOPROTEIN containing siroheme and can utilize both NAD and NADP as cofactors. This enzyme was formerly classified as EC Reductases: Oxidoreductases that are specific for the reduction of NITRATES.Sodium Nitrite: Nitrous acid sodium salt. Used in many industrial processes, in meat curing, coloring, and preserving, and as a reagent in ANALYTICAL CHEMISTRY TECHNIQUES. It is used therapeutically as an antidote in cyanide poisoning. The compound is toxic and mutagenic and will react in vivo with secondary or tertiary amines thereby producing highly carcinogenic nitrosamines.Ferredoxin-Nitrite Reductase: An IRON-containing protein that uses siroheme and 4Fe-4S iron-sulfur centers as prosthetic groups. It catalyzes the six-electron oxidation of AMMONIA to nitrite.Nitrates: Inorganic or organic salts and esters of nitric acid. These compounds contain the NO3- radical.Cytochromes a1: A subclass of heme a containing cytochromes have a reduced alpha-band absorption of 587-592 nm. They are primarily found in microorganisms.Nitrate Reductase: An enzyme that catalyzes the oxidation of nitrite to nitrate. It is a cytochrome protein that contains IRON and MOLYBDENUM.Alcaligenes: A genus of gram-negative, aerobic, motile bacteria that occur in water and soil. Some are common inhabitants of the intestinal tract of vertebrates. These bacteria occasionally cause opportunistic infections in humans.Alcaligenes faecalis: The type species of gram negative bacteria in the genus ALCALIGENES, found in soil. It is non-pathogenic, non-pigmented, and used for the production of amino acids.NADH, NADPH Oxidoreductases: A group of oxidoreductases that act on NADH or NADPH. In general, enzymes using NADH or NADPH to reduce a substrate are classified according to the reverse reaction, in which NAD+ or NADP+ is formally regarded as an acceptor. This subclass includes only those enzymes in which some other redox carrier is the acceptor. (Enzyme Nomenclature, 1992, p100) EC 1.6.Oxidoreductases: The class of all enzymes catalyzing oxidoreduction reactions. The substrate that is oxidized is regarded as a hydrogen donor. The systematic name is based on donor:acceptor oxidoreductase. The recommended name will be dehydrogenase, wherever this is possible; as an alternative, reductase can be used. Oxidase is only used in cases where O2 is the acceptor. (Enzyme Nomenclature, 1992, p9)Bacteroidaceae: A family of gram-negative bacteria found primarily in the intestinal tracts and mucous membranes of warm-blooded animals. Its organisms are sometimes pathogenic.Denitrification: Nitrate reduction process generally mediated by anaerobic bacteria by which nitrogen available to plants is converted to a gaseous form and lost from the soil or water column. It is a part of the nitrogen cycle.Cytochromes c1: The 30-kDa membrane-bound c-type cytochrome protein of mitochondria that functions as an electron donor to CYTOCHROME C GROUP in the mitochondrial and bacterial RESPIRATORY CHAIN. (From Enzyme Nomenclature, 1992, p545)Azurin: A bacterial protein from Pseudomonas, Bordetella, or Alcaligenes which operates as an electron transfer unit associated with the cytochrome chain. The protein has a molecular weight of approximately 16,000, contains a single copper atom, is intensively blue, and has a fluorescence emission band centered at 308nm.Oxidation-Reduction: A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).Cytochromes: Hemeproteins whose characteristic mode of action involves transfer of reducing equivalents which are associated with a reversible change in oxidation state of the prosthetic group. Formally, this redox change involves a single-electron, reversible equilibrium between the Fe(II) and Fe(III) states of the central iron atom (From Enzyme Nomenclature, 1992, p539). The various cytochrome subclasses are organized by the type of HEME and by the wavelength range of their reduced alpha-absorption bands.Paracoccus: Gram-negative non-motile bacteria found in soil or brines.Hydroxymethylglutaryl CoA Reductases: Enzymes that catalyze the reversible reduction of alpha-carboxyl group of 3-hydroxy-3-methylglutaryl-coenzyme A to yield MEVALONIC ACID.Heme: The color-furnishing portion of hemoglobin. It is found free in tissues and as the prosthetic group in many hemeproteins.Ribonucleotide ReductasesAnaerobiosis: The complete absence, or (loosely) the paucity, of gaseous or dissolved elemental oxygen in a given place or environment. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Dithionite: Dithionite. The dithionous acid ion and its salts.Cytochrome-B(5) Reductase: A FLAVOPROTEIN oxidoreductase that occurs both as a soluble enzyme and a membrane-bound enzyme due to ALTERNATIVE SPLICING of a single mRNA. The soluble form is present mainly in ERYTHROCYTES and is involved in the reduction of METHEMOGLOBIN. The membrane-bound form of the enzyme is found primarily in the ENDOPLASMIC RETICULUM and outer mitochondrial membrane, where it participates in the desaturation of FATTY ACIDS; CHOLESTEROL biosynthesis and drug metabolism. A deficiency in the enzyme can result in METHEMOGLOBINEMIA.Nitric Oxide: A free radical gas produced endogenously by a variety of mammalian cells, synthesized from ARGININE by NITRIC OXIDE SYNTHASE. Nitric oxide is one of the ENDOTHELIUM-DEPENDENT RELAXING FACTORS released by the vascular endothelium and mediates VASODILATION. It also inhibits platelet aggregation, induces disaggregation of aggregated platelets, and inhibits platelet adhesion to the vascular endothelium. Nitric oxide activates cytosolic GUANYLATE CYCLASE and thus elevates intracellular levels of CYCLIC GMP.Copper: A heavy metal trace element with the atomic symbol Cu, atomic number 29, and atomic weight 63.55.Electron Transport: The process by which ELECTRONS are transported from a reduced substrate to molecular OXYGEN. (From Bennington, Saunders Dictionary and Encyclopedia of Laboratory Medicine and Technology, 1984, p270)Nitrosomonas europaea: The type species of the genus NITROSOMONAS, a gram-negative chemolithotroph that oxidizes ammonia to nitrite. It is found in soil, sewage, freshwater, and on building walls, and especially in polluted areas where air contains high levels of nitrogen compounds.Paracoccus pantotrophus: A species of gram-negative, coccoid, mostly chemolithoautotrophic bacteria, in the family RHODOBACTERACEAE. Some strains can grow anaerobically.Hydroxylamines: Organic compounds that contain the (-NH2OH) radical.Spectrophotometry: The art or process of comparing photometrically the relative intensities of the light in different parts of the spectrum.Glutathione Reductase: Catalyzes the oxidation of GLUTATHIONE to GLUTATHIONE DISULFIDE in the presence of NADP+. Deficiency in the enzyme is associated with HEMOLYTIC ANEMIA. Formerly listed as EC Reductase: An enzyme that utilizes NADH or NADPH to reduce FLAVINS. It is involved in a number of biological processes that require reduced flavin for their functions such as bacterial bioluminescence. Formerly listed as EC and EC Reductase: A FLAVOPROTEIN enzyme that catalyzes the oxidation of THIOREDOXINS to thioredoxin disulfide in the presence of NADP+. It was formerly listed as EC Oxide: Nitrogen oxide (N2O). A colorless, odorless gas that is used as an anesthetic and analgesic. High concentrations cause a narcotic effect and may replace oxygen, causing death by asphyxia. It is also used as a food aerosol in the preparation of whipping cream.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.NADPH-Ferrihemoprotein Reductase: A flavoprotein that catalyzes the reduction of heme-thiolate-dependent monooxygenases and is part of the microsomal hydroxylating system. EC Iron-containing proteins that transfer electrons, usually at a low potential, to flavoproteins; the iron is not present as in heme. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)Ferredoxin-NADP Reductase: An enzyme that catalyzes the oxidation and reduction of FERREDOXIN or ADRENODOXIN in the presence of NADP. EC was formerly listed as EC and EC A colorless inorganic compound (HONH2) used in organic synthesis and as a reducing agent, due to its ability to donate nitric oxide.Wolinella: A genus of gram-negative, anaerobic, rod-shaped bacteria isolated from the bovine RUMEN, the human gingival sulcus, and dental PULPITIS infections.Amyl Nitrite: A vasodilator that is administered by inhalation. It is also used recreationally due to its supposed ability to induce euphoria and act as an aphrodisiac.Electron Spin Resonance Spectroscopy: A technique applicable to the wide variety of substances which exhibit paramagnetism because of the magnetic moments of unpaired electrons. The spectra are useful for detection and identification, for determination of electron structure, for study of interactions between molecules, and for measurement of nuclear spins and moments. (From McGraw-Hill Encyclopedia of Science and Technology, 7th edition) Electron nuclear double resonance (ENDOR) spectroscopy is a variant of the technique which can give enhanced resolution. Electron spin resonance analysis can now be used in vivo, including imaging applications such as MAGNETIC RESONANCE IMAGING.Cytochrome c Group: A group of cytochromes with covalent thioether linkages between either or both of the vinyl side chains of protoheme and the protein. (Enzyme Nomenclature, 1992, p539)Cytochrome ReductasesEctothiorhodospiraceae: A family in the order Chromatiales, class GAMMAPROTEOBACTERIA. These are haloalkaliphilic, phototrophic bacteria that deposit elemental sulfur outside their cells.Bacterial Proteins: Proteins found in any species of bacterium.Kinetics: The rate dynamics in chemical or physical systems.Pseudomonas: A genus of gram-negative, aerobic, rod-shaped bacteria widely distributed in nature. Some species are pathogenic for humans, animals, and plants.Aerobiosis: Life or metabolic reactions occurring in an environment containing oxygen.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Genes, Bacterial: The functional hereditary units of BACTERIA.Hyphomicrobium: A genus of rod-shaped, oval, or bean-shaped bacteria found in soil and fresh water. Polar prosthecae are present and cells reproduce by budding at the tips of the prosthecae. Cells of this genus are aerobic and grow best with one-carbon compounds. (From Bergey's Manual of Determinative Bacteriology, 9th ed)Sulfite Reductase (Ferredoxin): A FERREDOXIN-dependent oxidoreductase that is primarily found in PLANTS where it plays an important role in the assimilation of SULFUR atoms for the production of CYSTEINE and METHIONINE.Electron Transport Complex IV: A multisubunit enzyme complex containing CYTOCHROME A GROUP; CYTOCHROME A3; two copper atoms; and 13 different protein subunits. It is the terminal oxidase complex of the RESPIRATORY CHAIN and collects electrons that are transferred from the reduced CYTOCHROME C GROUP and donates them to molecular OXYGEN, which is then reduced to water. The redox reaction is simultaneously coupled to the transport of PROTONS across the inner mitochondrial membrane.Pseudomonas aeruginosa: A species of gram-negative, aerobic, rod-shaped bacteria commonly isolated from clinical specimens (wound, burn, and urinary tract infections). It is also found widely distributed in soil and water. P. aeruginosa is a major agent of nosocomial infection.Ralstonia pickettii: The type species in the genus RALSTONIA. It is often found in the hospital ward as a contaminant of antiseptic and disinfectant solutions.Paracoccus denitrificans: A species of bacteria isolated from soil.Escherichia coli: A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.Tetrahydrofolate Dehydrogenase: An enzyme of the oxidoreductase class that catalyzes the reaction 7,8-dihyrofolate and NADPH to yield 5,6,7,8-tetrahydrofolate and NADPH+, producing reduced folate for amino acid metabolism, purine ring synthesis, and the formation of deoxythymidine monophosphate. Methotrexate and other folic acid antagonists used as chemotherapeutic drugs act by inhibiting this enzyme. (Dorland, 27th ed) EC A genus of gram-negative, anaerobic, rod-shaped bacteria capable of reducing sulfur compounds to hydrogen sulfide. Organisms are isolated from anaerobic mud of fresh and salt water, animal intestines, manure, and feces.Nitrosomonas: A genus of gram-negative, ellipsoidal or rod-shaped bacteria whose major source of energy and reducing power is from the oxidation of ammonia to nitrite. Its species occur in soils, oceans, lakes, rivers, and sewage disposal systems.Oxidoreductases Acting on Sulfur Group Donors: Oxidoreductases with specificity for oxidation or reduction of SULFUR COMPOUNDS.Nitrogen: An element with the atomic symbol N, atomic number 7, and atomic weight [14.00643; 14.00728]. Nitrogen exists as a diatomic gas and makes up about 78% of the earth's atmosphere by volume. It is a constituent of proteins and nucleic acids and found in all living cells.Gene Expression Regulation, Bacterial: Any of the processes by which cytoplasmic or intercellular factors influence the differential control of gene action in bacteria.Quaternary Ammonium Compounds: Derivatives of ammonium compounds, NH4+ Y-, in which all four of the hydrogens bonded to nitrogen have been replaced with hydrocarbyl groups. These are distinguished from IMINES which are RN=CR2.Achromobacter denitrificans: The type species of gram negative, aerobic bacteria in the genus ACHROMOBACTER. Previously in the genus ALCALIGENES, the classification and nomenclature of this species has been frequently emended. The two subspecies, Achromobacter xylosoxidans subsp. denitrificans and Achromobacter xylosoxidans subsp. xylosoxidans are associated with infections.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Methylenetetrahydrofolate Reductase (NADPH2): A flavoprotein amine oxidoreductase that catalyzes the reversible conversion of 5-methyltetrahydrofolate to 5,10-methylenetetrahydrofolate. This enzyme was formerly classified as EC Viologen: 1,1'-Bis(phenylmethyl)4,4'-bipyridinium dichloride. Oxidation-reduction indicator.Ammonia: A colorless alkaline gas. It is formed in the body during decomposition of organic materials during a large number of metabolically important reactions. Note that the aqueous form of ammonia is referred to as AMMONIUM HYDROXIDE.Spectrum Analysis: The measurement of the amplitude of the components of a complex waveform throughout the frequency range of the waveform. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Nitrate Reductase (NADH): An NAD-dependent enzyme that catalyzes the oxidation of nitrite to nitrate. It is a FLAVOPROTEIN that contains IRON and MOLYBDENUM and is involved in the first step of nitrate assimilation in PLANTS; FUNGI; and BACTERIA. It was formerly classified as EC Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5'-phosphate (NMN) coupled by pyrophosphate linkage to the 5'-phosphate adenosine 2',5'-bisphosphate. It serves as an electron carrier in a number of reactions, being alternately oxidized (NADP+) and reduced (NADPH). (Dorland, 27th ed)Iron-Sulfur Proteins: A group of proteins possessing only the iron-sulfur complex as the prosthetic group. These proteins participate in all major pathways of electron transport: photosynthesis, respiration, hydroxylation and bacterial hydrogen and nitrogen fixation.Pulse Radiolysis: Use of a pulse of X-rays or fast electrons to generate free radicals for spectroscopic examination.Sulfites: Inorganic salts of sulfurous acid.Hemeproteins: Proteins that contain an iron-porphyrin, or heme, prosthetic group resembling that of hemoglobin. (From Lehninger, Principles of Biochemistry, 1982, p480)Methionine Sulfoxide Reductases: Reductases that catalyze the reaction of peptide-L-methionine -S-oxide + thioredoxin to produce peptide-L-methionine + thioredoxin disulfide + H(2)O.Hydroxymethylglutaryl-CoA Reductase Inhibitors: Compounds that inhibit HMG-CoA reductases. They have been shown to directly lower cholesterol synthesis.Ribonucleoside Diphosphate Reductase: An enzyme of the oxidoreductase class that catalyzes the formation of 2'-deoxyribonucleotides from the corresponding ribonucleotides using NADPH as the ultimate electron donor. The deoxyribonucleoside diphosphates are used in DNA synthesis. (From Dorland, 27th ed) EC Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Binding Sites: The parts of a macromolecule that directly participate in its specific combination with another molecule.Sequence Homology, Amino Acid: The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species.Hydrogen-Ion Concentration: The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH = log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Dihydropteridine Reductase: An enzyme that catalyzes the reduction of 6,7-dihydropteridine to 5,6,7,8-tetrahydropteridine in the presence of NADP+. Defects in the enzyme are a cause of PHENYLKETONURIA II. Formerly listed as EC c2: Type C cytochromes that are small (12-14 kD) single-heme proteins. They function as mobile electron carriers between membrane-bound enzymes in photosynthetic BACTERIA.Rhodobacter sphaeroides: Spherical phototrophic bacteria found in mud and stagnant water exposed to light.Oxygen: An element with atomic symbol O, atomic number 8, and atomic weight [15.99903; 15.99977]. It is the most abundant element on earth and essential for respiration.Cloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Quinone Reductases: NAD(P)H:(quinone acceptor) oxidoreductases. A family that includes three enzymes which are distinguished by their sensitivity to various inhibitors. EC (NAD(P)H DEHYDROGENASE (QUINONE);) is a flavoprotein which reduces various quinones in the presence of NADH or NADPH and is inhibited by dicoumarol. EC (NADH dehydrogenase (quinone)) requires NADH, is inhibited by AMP and 2,4-dinitrophenol but not by dicoumarol or folic acid derivatives. EC (NADPH dehydrogenase (quinone)) requires NADPH and is inhibited by dicoumarol and folic acid derivatives but not by 2,4-dinitrophenol.Metalloproteins: Proteins that have one or more tightly bound metal ions forming part of their structure. (Dorland, 28th ed)Sequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.Electrons: Stable elementary particles having the smallest known negative charge, present in all elements; also called negatrons. Positively charged electrons are called positrons. The numbers, energies and arrangement of electrons around atomic nuclei determine the chemical identities of elements. Beams of electrons are called CATHODE RAYS.Thiosulfates: Inorganic salts of thiosulfuric acid possessing the general formula R2S2O3.Alcohol Oxidoreductases: A subclass of enzymes which includes all dehydrogenases acting on primary and secondary alcohols as well as hemiacetals. They are further classified according to the acceptor which can be NAD+ or NADP+ (subclass 1.1.1), cytochrome (1.1.2), oxygen (1.1.3), quinone (1.1.5), or another acceptor (1.1.99).Simazine: A triazine herbicide.Oxidoreductases Acting on CH-CH Group Donors: A subclass of enzymes which includes all dehydrogenases acting on carbon-carbon bonds. This enzyme group includes all the enzymes that introduce double bonds into substrates by direct dehydrogenation of carbon-carbon single bonds.Flavins: Derivatives of the dimethylisoalloxazine (7,8-dimethylbenzo[g]pteridine-2,4(3H,10H)-dione) skeleton. Flavin derivatives serve an electron transfer function as ENZYME COFACTORS in FLAVOPROTEINS.Catalysis: The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.Paraquat: A poisonous dipyridilium compound used as contact herbicide. Contact with concentrated solutions causes irritation of the skin, cracking and shedding of the nails, and delayed healing of cuts and wounds.Thioredoxin Reductase 1: A subtype of thioredoxin reductase found primarily in the CYTOSOL.Bacteria: One of the three domains of life (the others being Eukarya and ARCHAEA), also called Eubacteria. They are unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal. Bacteria can be classified by their response to OXYGEN: aerobic, anaerobic, or facultatively anaerobic; by the mode by which they obtain their energy: chemotrophy (via chemical reaction) or PHOTOTROPHY (via light reaction); for chemotrophs by their source of chemical energy: CHEMOLITHOTROPHY (from inorganic compounds) or chemoorganotrophy (from organic compounds); and by their source for CARBON; NITROGEN; etc.; HETEROTROPHY (from organic sources) or AUTOTROPHY (from CARBON DIOXIDE). They can also be classified by whether or not they stain (based on the structure of their CELL WALLS) with CRYSTAL VIOLET dye: gram-negative or gram-positive.Models, Molecular: Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.Carbon Monoxide: Carbon monoxide (CO). A poisonous colorless, odorless, tasteless gas. It combines with hemoglobin to form carboxyhemoglobin, which has no oxygen carrying capacity. The resultant oxygen deprivation causes headache, dizziness, decreased pulse and respiratory rates, unconsciousness, and death. (From Merck Index, 11th ed)Dianisidine: Highly toxic compound which can cause skin irritation and sensitization. It is used in manufacture of azo dyes.Chromatiaceae: A family of phototrophic purple sulfur bacteria that deposit globules of elemental sulfur inside their cells. They are found in diverse aquatic environments.Enoyl-(Acyl-Carrier-Protein) Reductase (NADH): An NAD-dependent enzyme that catalyzes the oxidation of acyl-[acyl-carrier protein] to trans-2,3-dehydroacyl-[acyl-carrier protein]. It has a preference for acyl groups with a carbon chain length between 4 to 16.Nitrogen Oxides: Inorganic oxides that contain nitrogen.Viologens: A group of dipyridinium chloride derivatives that are used as oxidation-reduction indicators. The general formula is 1,1'-di-R-4,4'-bipyridinium chloride, where R = methyl, ethyl, benzyl or, betaine.Crystallography, X-Ray: The study of crystal structure using X-RAY DIFFRACTION techniques. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Hemoglobins: The oxygen-carrying proteins of ERYTHROCYTES. They are found in all vertebrates and some invertebrates. The number of globin subunits in the hemoglobin quaternary structure differs between species. Structures range from monomeric to a variety of multimeric arrangements.Protein Conformation: The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).Tungsten Compounds: Inorganic compounds that contain tungsten as an integral part of the molecule.Spectrophotometry, Ultraviolet: Determination of the spectra of ultraviolet absorption by specific molecules in gases or liquids, for example Cl2, SO2, NO2, CS2, ozone, mercury vapor, and various unsaturated compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)

Denitrifying Pseudomonas aeruginosa: some parameters of growth and active transport. (1/435)

Optimal cell yield of Pseudomonas aeruginosa grown under denitrifying conditions was obtained with 100 mM nitrate as the terminal electron acceptor, irrespective of the medium used. Nitrite as the terminal electron acceptor supported poor denitrifying growth when concentrations of less than 15 mM, but not higher, were used, apparently owing to toxicity exerted by nitrite. Nitrite accumulated in the medium during early exponential phase when nitrate was the terminal electron acceptor and then decreased to extinction before midexponential phase. The maximal rate of glucose and gluconate transport was supported by 1 mM nitrate or nitrite as the terminal electron acceptor under anaerobic conditions. The transport rate was greater with nitrate than with nitrite as the terminal electron acceptor, but the greatest transport rate was observed under aerobic conditions with oxygen as the terminal electron acceptor. When P. aeruginosa was inoculated into a denitrifying environment, nitrate reductase was detected after 3 h of incubation, nitrite reductase was detected after another 4 h of incubation, and maximal nitrate and nitrite reductase activities peaked together during midexponential phase. The latter coincided with maximal glucose transport activity.  (+info)

Molecular characterization of the nitrite-reducing system of Staphylococcus carnosus. (2/435)

Characterization of a nitrite reductase-negative Staphylococcus carnosus Tn917 mutant led to the identification of the nir operon, which encodes NirBD, the dissimilatory NADH-dependent nitrite reductase; SirA, the putative oxidase and chelatase, and SirB, the uroporphyrinogen III methylase, both of which are necessary for biosynthesis of the siroheme prosthetic group; and NirR, which revealed no convincing similarity to proteins with known functions. We suggest that NirR is essential for nir promoter activity. In the absence of NirR, a weak promoter upstream of sirA seems to drive transcription of sirA, nirB, nirD, and sirB in the stationary-growth phase. In primer extension experiments one predominant and several weaker transcription start sites were identified in the nir promoter region. Northern blot analyses indicated that anaerobiosis and nitrite are induction factors of the nir operon: cells grown aerobically with nitrite revealed small amounts of full-length transcript whereas cells grown anaerobically with or without nitrite showed large amounts of full-length transcript. Although a transcript is detectable, no nitrite reduction occurs in cells grown aerobically with nitrite, indicating an additional oxygen-controlled step at the level of translation, enzyme folding, assembly, or insertion of prosthetic groups. The nitrite-reducing activity expressed during anaerobiosis is switched off reversibly when the oxygen tension increases, most likely due to competition for electrons with the aerobic respiratory chain. Another gene, nirC, is located upstream of the nir operon. nirC encodes a putative integral membrane-spanning protein of unknown function. A nirC mutant showed no distinct phenotype.  (+info)

The GATA factor AreA is essential for chromatin remodelling in a eukaryotic bidirectional promoter. (3/435)

The linked niiA and niaD genes of Aspergillus nidulans are transcribed divergently. The expression of these genes is subject to a dual control system. They are induced by nitrate and repressed by ammonium. AreA mediates derepression in the absence of ammonium and NirA supposedly mediates nitrate induction. Out of 10 GATA sites, a central cluster (sites 5-8) is responsible for approximately 80% of the transcriptional activity of the promoter on both genes. We show occupancy in vivo of site 5 by the AreA protein, even under conditions of repression. Sites 5-8 are situated in a pre-set nucleosome-free region. Under conditions of expression, a drastic nucleosomal rearrangement takes place and the positioning of at least five nucleosomes flanking the central region is lost. Remodelling is strictly dependent on the presence of an active areA gene product, and independent from the NirA-specific and essential transcription factor. Thus, nucleosome remodelling is independent from the transcriptional activation of the niiA-niaD promoter. The results presented cast doubts on the role of NirA as the unique transducer of the nitrate induction signal. We demonstrate, for the first time in vivo, that a GATA factor is involved directly in chromatin remodelling.  (+info)

Nitrite reductase from Pseudomonas aeruginosa released by antimicrobial agents and complement induces interleukin-8 production in bronchial epithelial cells. (4/435)

We have recently reported that nitrite reductase, a bifunctional enzyme located in the periplasmic space of Pseudomonas aeruginosa, could induce interleukin-8 (IL-8) generation in a variety of respiratory cells, including bronchial epithelial cells (K. Oishi et al. Infect. Immun. 65:2648-2655, 1997). In this report, we examined the mode of nitrite reductase (PNR) release from a serum-sensitive strain of live P. aeruginosa cells during in vitro treatment with four different antimicrobial agents or human complement. Bacterial killing of P. aeruginosa by antimicrobial agents induced PNR release and mediated IL-8 production in human bronchial epithelial (BET-1A) cells. Among these agents, imipenem demonstrated rapid killing of P. aeruginosa as well as rapid release of PNR and resulted in the highest IL-8 production. Complement-mediated killing of P. aeruginosa was also associated with PNR release and enhanced IL-8 production. The immunoprecipitates of the aliquots of bacterial culture containing imipenem or complement with anti-PNR immunoglobulin G (IgG) induced twofold-higher IL-8 production than did the immunoprecipitates of the aliquots of bacterial culture with a control IgG. These pieces of evidence confirmed that PNR released in the aliquots of bacterial culture was responsible for IL-8 production in the BET-1A cells. Furthermore, the culture supernatants of the BET-1A cells stimulated with aliquots of bacterial culture containing antimicrobial agents or complement similarly mediated neutrophil migration in vitro. These data support the possibility that a potent inducer of IL-8, PNR, could be released from P. aeruginosa after exposure to antimicrobial agents or complement and contributes to neutrophil migration in the airways during bronchopulmonary infections with P. aeruginosa.  (+info)

PCR detection of genes encoding nitrite reductase in denitrifying bacteria. (5/435)

Using consensus regions in gene sequences encoding the two forms of nitrite reductase (Nir), a key enzyme in the denitrification pathway, we designed two sets of PCR primers to amplify cd1- and Cu-nir. The primers were evaluated by screening defined denitrifying strains, denitrifying isolates from wastewater treatment plants, and extracts from activated sludge. Sequence relationships of nir genes were also established. The cd1 primers were designed to amplify a 778 to 799-bp region of cd1-nir in the six published sequences. Likewise, the Cu primers amplified a 473-bp region in seven of the eight published Cu-nir sequences. Together, the two sets of PCR primers amplified nir genes in nine species within four genera, as well as in four of the seven sludge isolates. The primers did not amplify genes of nondenitrifying strains. The Cu primers amplified the expected fragment in all 13 sludge samples, but cd1-nir fragments were only obtained in five samples. PCR products of the expected sizes were verified as nir genes after hybridization to DNA probes, except in one case. The sequenced nir fragments were related to other nir sequences, demonstrating that the primers amplified the correct gene. The selected primer sites for Cu-nir were conserved, while broad-range primers targeting conserved regions of cd1-nir seem to be difficult to find. We also report on the existence of Cu-nir in Paracoccus denitrificans Pd1222.  (+info)

The blue copper-containing nitrite reductase from Alcaligenes xylosoxidans: cloning of the nirA gene and characterization of the recombinant enzyme. (6/435)

The nirA gene encoding the blue dissimilatory nitrite reductase from Alcaligenes xylosoxidans has been cloned and sequenced. To our knowledge, this is the first report of the characterization of a gene encoding a blue copper-containing nitrite reductase. The deduced amino acid sequence exhibits a high degree of similarity to other copper-containing nitrite reductases from various bacterial sources. The full-length protein included a 24-amino-acid leader peptide. The nirA gene was overexpressed in Escherichia coli and was shown to be exported to the periplasm. Purification was achieved in a single step, and analysis of the recombinant Nir enzyme revealed that cleavage of the signal peptide occurred at a position identical to that for the native enzyme isolated from A. xylosoxidans. The recombinant Nir isolated directly was blue and trimeric and, on the basis of electron paramagnetic resonance spectroscopy and metal analysis, possessed only type 1 copper centers. This type 2-depleted enzyme preparation also had a low nitrite reductase enzyme activity. Incubation of the periplasmic fraction with copper sulfate prior to purification resulted in the isolation of an enzyme with a full complement of type 1 and type 2 copper centers and a high specific activity. The kinetic properties of the recombinant enzyme were indistinguishable from those of the native nitrite reductase isolated from A. xylosoxidans. This rapid isolation procedure will greatly facilitate genetic and biochemical characterization of both wild-type and mutant derivatives of this protein.  (+info)

Bacterial nitric oxide synthesis. (7/435)

The structure-function relationships in nitrite reductases, key enzymes in the dissimilatory denitrification pathway which reduce nitrite to nitric oxide (NO), are reviewed in this paper. The mechanisms of NO production are discussed in detail and special attention is paid to new structural information, such as the high resolution structure of the copper- and heme-containing enzymes from different sources. Finally, some implications relevant to regulation of the steady state levels of NO in denitrifiers are presented.  (+info)

Does the reduction of c heme trigger the conformational change of crystalline nitrite reductase? (8/435)

The structures of nitrite reductase from Paracoccus denitrificans GB17 (NiR-Pd) and Pseudomonas aeruginosa (NiR-Pa) have been described for the oxidized and reduced state (Fulop, V., Moir, J. W. B., Ferguson, S. J., and Hajdu, J. (1995) Cell 81, 369-377; Nurizzo, D., Silvestrini, M. C., Mathieu, M., Cutruzzola, F., Bourgeois, D., Fulop, V., Hajdu, J., Brunori, M., Tegoni, M., and Cambillau, C. (1997) Structure 5, 1157-1171; Nurizzo, D., Cutruzzola, F., Arese, M., Bourgeois, D., Brunori, M., Cambillau, C. , and Tegoni, M. (1998) Biochemistry 37, 13987-13996). Major conformational rearrangements are observed in the extreme states although they are more substantial in NiR-Pd. The four structures differ significantly in the c heme domains. Upon reduction, a His17/Met106 heme-ligand switch is observed in NiR-Pd together with concerted movements of the Tyr in the distal site of the d1 heme (Tyr10 in NiR-Pa, Tyr25 in NiR-Pd) and of a loop of the c heme domain (56-62 in NiR-Pa, 99-116 in NiR-Pd). Whether the reduction of the c heme, which undergoes the major rearrangements, is the trigger of these movements is the question addressed by our study. This conformational reorganization is not observed in the partially reduced species, in which the c heme is partially or largely (15-90%) reduced but the d1 heme is still oxidized. These results suggest that the d1 heme reduction is likely to be responsible of the movements. We speculate about the mechanistic explanation as to why the opening of the d1 heme distal pocket only occurs upon electron transfer to the d1 heme itself, to allow binding of the physiological substrate NO2- exclusively to the reduced metal center.  (+info)

  • Using a linker that harbors a gatekeeper tyrosine in a nitrite access channel, the tethered haem domain enables catalysis by other mechanisms. (
  • In contrast to S. oneidensis MR-1, a biotic transitory nitrite accumulation at the expense of ammonium was observed in S. algae during anaerobic growth with Mn(IV) under condition of limiting electron acceptor, concomitantly, with a higher electron donor stoichiometry than expected. (
  • Recently, the structure of a Cu-containing nitrite reductase (NiR) from Hyphomicrobium denitrificans ( Hd NiR) has been reported, establishing the existence of a new family of Cu-NiR where an additional type 1 Cu (T1Cu) containing cupredoxin domain is located at the N-terminus (Nojiri et al. (
  • In enzymology, a ferredoxin-nitrite reductase (EC is an enzyme that catalyzes the chemical reaction NH3 + 2 H2O + 6 oxidized ferredoxin ⇌ {\displaystyle \rightleftharpoons } nitrite + 6 reduced ferredoxin + 7 H+ The 3 substrates of this enzyme are NH3, H2O, and oxidized ferredoxin, whereas its 3 products are nitrite, reduced ferredoxin, and H+. (
  • Below are the list of possible Ferredoxin--nitrite reductase products. (
  • These results shed light on the mechanistic details of the activity of cd 1 nitrite reductases and on the biological role of the d 1 -haem, whose presence in this class of enzymes has to date been unexplained. (
  • In aerobic soils, nitrate is the dominant species and it is converted to ammonium by the sequential action of two enzymes, nitrate reductase (NR) and nitrite reductase (NiR) (Dechorgnat et al. (
  • However, with the exception of nitrate reductase, the corresponding enzymes are yet to be identified, and understanding NO generation in plants remains an important challenge [ 4 , 5 ]. (
  • The proton transfer from His244 to nitrite bound on the T2 Cu site via the hydrogen bond network induced intra-electron transfer from the T1 to T2 Cu site. (
  • Recently, the structure of a Cu-containing nitrite reductase (NiR) from Hyphomicrobium denitrificans ( Hd NiR) has been reported, establishing the existence of a new family of Cu-NiR where an additional type 1 Cu (T1Cu) containing cupredoxin domain is located at the N-terminus (Nojiri et al. (
  • We determined 12 key high-resolution structures of sulfite reductase hemoprotein that characterize its active center in 3 different states of oxidation and its interactions with substrates, inhibitors, intermediates, and products. (
  • We used multiwavelength anomalous diffraction of the native siroheme, an iron-containing macrocycle of the isobacteriochlorin class, and Fe 4 S 4 cluster cofactors to solve the atomic-resolution structure of the hemoprotein from sulfite reductase hemoprotein. (
  • Several lines of evidence indicate that NO can be synthesized in plants from nitrite, polyamines and L-arginine, through nonenzymatic or enzymatic mechanisms [ 3 , 4 ]. (
  • The addition of nitrite, but not nitrate, is reported to further elevate nrfA expression via either the NarL or NarP response regulators. (