Nitric oxide contrasts with most intercellular messengers because it diffuses rapidly and isotropically through most tissues with little reaction but cannot be transported through the vasculature due to rapid destruction by oxyhemoglobin. The rapid diffusion of nitric oxide between cells allows it to locally integrate the responses of blood vessels to turbulence, modulate synaptic plasticity in neurons, and control the oscillatory behavior of neuronal networks. Nitric oxide is not necessarily short lived and is intrinsically no more reactive than oxygen. The reactivity of nitric oxide per se has been greatly overestimated in vitro because no drain is provided to remove nitric oxide. Nitric oxide persists in solution for several minutes in micromolar concentrations before it reacts with oxygen to form much stronger oxidants like nitrogen dioxide. Nitric oxide is removed within seconds in vivo by diffusion over 100 microns through tissues to enter red blood cells and react with oxyhemoglobin. The direct toxicity of nitric oxide is modest but is greatly enhanced by reacting with superoxide to form peroxynitrite (ONOO-). Nitric oxide is the only biological molecule produced in high enough concentrations to out-compete superoxide dismutase for superoxide. Peroxynitrite reacts relatively slowly with most biological molecules, making peroxynitrite a selective oxidant. Peroxynitrite modifies tyrosine in proteins to create nitrotyrosines, leaving a footprint detectable in vivo. Nitration of structural proteins, including neurofilaments and actin, can disrupt filament assembly with major pathological consequences. Antibodies to nitrotyrosine have revealed nitration in human atherosclerosis, myocardial ischemia, septic and distressed lung, inflammatory bowel disease, and amyotrophic lateral sclerosis.

Nitric oxide, superoxide, and peroxynitrite: the good, the bad, and ugly.

Denitrification is a distinct means of energy conservation, making use of N oxides as terminal electron acceptors for cellular bioenergetics under anaerobic, microaerophilic, and occasionally aerobic conditions. The process is an essential branch of the global N cycle, reversing dinitrogen fixation, and is associated with chemolithotrophic, phototrophic, diazotrophic, or organotrophic metabolism but generally not with obligately anaerobic life. Discovered more than a century ago and believed to be exclusively a bacterial trait, denitrification has now been found in halophilic and hyperthermophilic archaea and in the mitochondria of fungi, raising evolutionarily intriguing vistas. Important advances in the biochemical characterization of denitrification and the underlying genetics have been achieved with Pseudomonas stutzeri, Pseudomonas aeruginosa, Paracoccus denitrificans, Ralstonia eutropha, and Rhodobacter sphaeroides. Pseudomonads represent one of the largest assemblies of the denitrifying bacteria within a single genus, favoring their use as model organisms. Around 50 genes are required within a single bacterium to encode the core structures of the denitrification apparatus. Much of the denitrification process of gram-negative bacteria has been found confined to the periplasm, whereas the topology and enzymology of the gram-positive bacteria are less well established. The activation and enzymatic transformation of N oxides is based on the redox chemistry of Fe, Cu, and Mo. Biochemical breakthroughs have included the X-ray structures of the two types of respiratory nitrite reductases and the isolation of the novel enzymes nitric oxide reductase and nitrous oxide reductase, as well as their structural characterization by indirect spectroscopic means. This revealed unexpected relationships among denitrification enzymes and respiratory oxygen reductases. Denitrification is intimately related to fundamental cellular processes that include primary and secondary transport, protein translocation, cytochrome c biogenesis, anaerobic gene regulation, metalloprotein assembly, and the biosynthesis of the cofactors molybdopterin and heme D1. An important class of regulators for the anaerobic expression of the denitrification apparatus are transcription factors of the greater FNR family. Nitrate and nitric oxide, in addition to being respiratory substrates, have been identified as signaling molecules for the induction of distinct N oxide-metabolizing enzymes.

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Cell biology and molecular basis of denitrification.

Nitric oxide (NO.), a potentially toxic molecule, has been implicated in a wide range of biological functions. Details of its biochemistry, however, remain poorly understood. The broader chemistry of nitrogen monoxide (NO) involves a redox array of species with distinctive properties and reactivities: NO+ (nitrosonium), NO., and NO- (nitroxyl anion). The integration of this chemistry with current perspectives of NO biology illuminates many aspects of NO biochemistry, including the enzymatic mechanism of synthesis, the mode of transport and targeting in biological systems, the means by which its toxicity is mitigated, and the function-regulating interaction with target proteins.

https://science.sciencemag.org/content/sci/258/5090/1898.full.pdf

Biochemistry of nitric oxide and its redox-activated forms

The rate constant for the reaction of NO with ·O2− was determined to be (6.7 ± 0.9) × 109 1 mol−1 s−1, considerably higher than previously reported. Rate measurements were made from pH 5.6 to 12.5 ...

The reaction of no with superoxide

Peroxynitrite-mediated tyrosine nitration catalyzed by superoxide dismutase

Thermal decomposition of oxyhyponitrite (sodium trioxodinitrate(II)) in aqueous solution

Etude de la decomposition photochimique du trioxodinitrate; l'intermediaire reactif NO − peut apparaitre dans les etats singulet et triplet. Cinetique d'ordre 0

Photolysis of the nitrogen-nitrogen double bond in trioxodinitrate: reaction between triplet oxonitrate(1-) and molecular oxygen to form peroxonitrite

Decomposition of N-hydroxybenzenesulfonamide (C 6 H 5 SO 2 NHOH) in alkaline solution to yield N 2 O and sulfinate (C 6 H 5 SO 2 - ) is first order in C 6 H 5 SO 2 NHO - , with rate constant=2.44 (±0.23)×10 -4 s -1 at 25 o C, ΔH=94.1 kJ mol -1 , and ΔS=6.64 J K -1 mol -1

Kinetic, isotopic, and nitrogen-15 NMR study of N-hydroxybenzenesulfonamide decomposition: an nitrosyl hydride (HNO) source reaction

Ground-water samples from two heavily fertilized sites in Suffolk County, New York, were collected through the 1978 growing season and analyzed for nitrate-N concentrations and nitrogen-isotope ratios. Six wells were at a potato farm; six were on a golf course. The purpose of this study was to determine whether the 15N/14N ratios (δ15N values) of fertilizer are increased during transit from land surface to ground water to an extent which would preclude use of this ratio to distinguish agricultural from animal sources of nitrate in ground water.



Ground water at both sites contained a greater proportion of 15N than the fertilizers being applied. At the potato farm, the average δ15N value of the fertilizers was 0.2%0; the average δ15N value of the ground-water nitrate was 6.2 %0. At the golf course, the average δ15N value of the fertilizers was -5.9%0, and that of ground-water nitrate was 6.5%0. The higher δ15N values of ground-water nitrate are probably caused by isotopic fractionation during the volatile loss of ammonia from nitrogen applied in reduced forms (NH+4 and organic-N).



The δ15N values of most ground-water samples from both areas were less than 10%0, the upper limit of the range characteristic of agricultural sources of nitrate; these sources include both fertilizer nitrate and nitrate derived from increased mineralization of soil nitrogen through cultivation. Previous studies have shown that the S15N values of nitrate derived from human or animal waste generally exceed 10%0. The nitrogen-isotope ratios of fertilizer-derived nitrate were not altered to an extent that would make them indistinguishable from animal-waste-derived nitrates in ground water.

Nitrogen‐Isotope Ratios of Nitrate in Ground Water Under Fertilized Fields, Long Island, New York

Recent developments in the aqueous solution chemistry of nitrogen are described, with particular attention to the low positive oxidation states +1 and +2. The compounds discussed include hyponitrous acid and hyponitrites, nitrosyl hydride (HNO, “nitroxyl”), trioxodinitrate, nitric oxide, and nitroamine. The numerous redox pathways in which these and other nitrogen compounds are participants illustrate the versatility of that element, and bear important relation to current problems in nitrogen cycle research that focus upon the identity and reactivity of nitrogen species in intermediate oxidation states.

Francis T. Bonner

Papers

Thermal decomposition of oxyhyponitrite (sodium trioxodinitrate(II)) in aqueous solution

Photolysis of the nitrogen-nitrogen double bond in trioxodinitrate: reaction between triplet oxonitrate(1-) and molecular oxygen to form peroxonitrite

Kinetic, isotopic, and nitrogen-15 NMR study of N-hydroxybenzenesulfonamide decomposition: an nitrosyl hydride (HNO) source reaction

Nitrogen‐Isotope Ratios of Nitrate in Ground Water Under Fertilized Fields, Long Island, New York

The Aqueous Solution Chemistry of Nitrogen in Low Positive Oxidation States