Nitrite

About: Nitrite is a research topic. Over the lifetime, 15425 publications have been published within this topic receiving 484581 citations.

Reactions between Nitric Oxide, Superoxide, and Peroxynitrite: Footprints of Peroxynitrite in Vivo

Abstract: Publisher Summary This chapter examines a number of reaction pathways for nitric oxide, with the emphasis on assessing their biological relevance. Till date, the fastest reaction for nitric oxide with clear toxicological significance is that with superoxide to produce ONOO − . Thus, the chemistry and reactivity of ONOO − are discussed at length. In addition, the interaction between ONOO − and nitric oxide is examined with respect to its effects on nitric oxide half-life as well as effects on peroxynitrite reactivity toward phenol. Reaction mechanisms are proposed to account for the nitrated, hydroxylated, and nitrosated phenolic products available. The primary reactions of nitric oxide are almost exclusively limited to other species possessing unpaired electrons, such as the iron in heme proteins, as well as nonheme iron and superoxide. Nitric oxide does react with molecular oxygen; however, this reaction occurs so slowly at physiological concentrations as to be toxicologically insignificant. Primary reactions of nitric oxide can result in a variety of secondary products ranging from innocuous nitrate (NO −3 ), nitrite (NO −2 ) and nitroxyl (NO − ) to reactive intermediates such as nitrosonium (NO + ), peroxynitrite (ONOO − ), and nitrogen dioxide (NO 2 ). The predominant end products of these reactive intermediates that are stable enough to be measured in biological systems include nitrite, nitrate, nitrotyrosine, and various nitrosothiols.

Electrocatalytic reduction of nitrite and nitric oxide to ammonia with iron-substituted polyoxotungstates

Abstract: Heteropolytungstates in which one of the positions normally occupied by a tungsten cation is occupied instead by an iron cation are shown to be catalysts for the electroreduction of nitrite to ammonia. The lacunary derivatives in which the empty tungsten site is unoccupied show no catalytic activity. The catalytic mechanism involves the intermediate formation of a nitrosyl complex of the Fe(II) form of the catalyst. The pH dependence of the rate of formation of the nitrosyl complex shows that nitrous acid is the reactive form of nitrite between pH 2 and 8. The catalyzed reduction does not produce hydroxylamine as an intermediate and appears to depend upon the ability of the multiply reduced heteropolytungstates to deliver electrons to the NO group bound to the iron center in a concerted, multiple-electron step. The iron-substituted heteropolytungstates are not degraded by repeated cycling between their oxidized and reduced states. A particularly valuable feature of the heteropolytungstate is the ease with which the formal potentials of the several redox couples they exhibit may be shifted by changing the identity of the central heteroatom. Exploitation of this feature provides diagnostic information that can be decisive in establishing the mechanism of electrocatalytic processes.

Circulating Nitrite Contributes to Cardioprotection by Remote Ischemic Preconditioning

Abstract: Rationale: Remote ischemic preconditioning (rIPC) with short episodes of ischemia/reperfusion (I/R) of an organ remote from the heart is a powerful approach to protect against myocardial I/R injury. The signal transduction pathways for the cross talk between the remote site and the heart remain unclear in detail. Objective: To elucidate the role of circulating nitrite in cardioprotection by rIPC. Methods and Results: Mice were subjected to 4 cycles of no-flow ischemia with subsequent reactive hyperemia within the femoral region and underwent in vivo myocardial I/R (30 minutes/5 minutes or 24 hours). The mouse experiments were conducted using genetic and pharmacological approaches. Shear stress–dependent stimulation of endothelial nitric oxide synthase within the femoral artery during reactive hyperemia yielded substantial release of nitric oxide, subsequently oxidized to nitrite and transferred humorally to the myocardium. Within the heart, reduction of nitrite to nitric oxide by cardiac myoglobin and subsequent S -nitrosation of mitochondrial membrane proteins reduced mitochondrial respiration, reactive oxygen species formation, and myocardial infarct size. Pharmacological and genetic inhibition of nitric oxide/nitrite generation by endothelial nitric oxide synthase at the remote site or nitrite bioactivation by myoglobin within the target organ abrogated the cardioprotection by rIPC. Transfer experiments of plasma from healthy volunteers subjected to rIPC of the arm identified plasma nitrite as a cardioprotective agent in isolated Langendorff mouse heart preparations exposed to I/R. Conclusions: Circulating nitrite derived from shear stress–dependent stimulation of endothelial nitric oxide synthase at the remote site of rIPC contributes to cardioprotection during I/R. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT01259739.

Nitric oxide is an obligate bacterial nitrification intermediate produced by hydroxylamine oxidoreductase

Abstract: Ammonia (NH 3 )-oxidizing bacteria (AOB) emit substantial amounts of nitric oxide (NO) and nitrous oxide (N 2 O), both of which contribute to the harmful environmental side effects of large-scale agriculture. The currently accepted model for AOB metabolism involves NH 3 oxidation to nitrite (NO 2 – ) via a single obligate intermediate, hydroxylamine (NH 2 OH). Within this model, the multiheme enzyme hydroxylamine oxidoreductase (HAO) catalyzes the four-electron oxidation of NH 2 OH to NO 2 – . We provide evidence that HAO oxidizes NH 2 OH by only three electrons to NO under both anaerobic and aerobic conditions. NO 2 – observed in HAO activity assays is a nonenzymatic product resulting from the oxidation of NO by O 2 under aerobic conditions. Our present study implies that aerobic NH 3 oxidation by AOB occurs via two obligate intermediates, NH 2 OH and NO, necessitating a mediator of the third enzymatic step.