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.

Evolution has resorted to nitric oxide (NO), a tiny, reactive radical gas, to mediate both servoregulatory and cytotoxic functions. This article reviews how different forms of nitric oxide synthase help confer specificity and diversity on the effects of this remarkable signaling molecule.

https://faseb.onlinelibrary.wiley.com/doi/pdf/10.1096/fasebj.6.12.1381691

Nitric oxide as a secretory product of mammalian cells.

This review concentrates on advances in nitric oxide synthase (NOS) structure, function and inhibition made in the last seven years, during which time substantial advances have been made in our understanding of this enzyme family. There is now information on the enzyme structure at all levels from primary (amino acid sequence) to quaternary (dimerization, association with other proteins) structure. The crystal structures of the oxygenase domains of inducible NOS (iNOS) and vascular endothelial NOS (eNOS) allow us to interpret other information in the context of this important part of the enzyme, with its binding sites for iron protoporphyrin IX (haem), biopterin, L-arginine, and the many inhibitors which interact with them. The exact nature of the NOS reaction, its mechanism and its products continue to be sources of controversy. The role of the biopterin cofactor is now becoming clearer, with emerging data implicating one-electron redox cycling as well as the multiple allosteric effects on enzyme activity. Regulation of the NOSs has been described at all levels from gene transcription to covalent modification and allosteric regulation of the enzyme itself. A wide range of NOS inhibitors have been discussed, interacting with the enzyme in diverse ways in terms of site and mechanism of inhibition, time-dependence and selectivity for individual isoforms, although there are many pitfalls and misunderstandings of these aspects. Highly selective inhibitors of iNOS versus eNOS and neuronal NOS have been identified and some of these have potential in the treatment of a range of inflammatory and other conditions in which iNOS has been implicated.

/pdf/nitric-oxide-synthases-structure-function-and-inhibition-1t31plqilr.pdf

Nitric oxide synthases: structure, function and inhibition

A rapid, simple spectrophotometric method for simultaneous detection of nitrate and nitrite.

Nitric oxide is an inorganic free radical gas, of formula *N=O (abbreviated as NO). The discovery in 1987/88 that vascular endothelial cells are able to synthesize NO from L-arginine as a transcellular signal [1-4] was initially received by most biologists with considerable scepticism. By now, however, the existence of the L-arginine:NO pathway has been thoroughly documented and its relevance in biology is slowly being unravelled. All of this has led to the appearance of a new and vigorous field of research, as evidenced by the increasing number of publications relating to NO and NO synthases (Figure 1). This review will describe the known biochemical mechanisms involved in the synthesis of NO from L-arginine by the NO synthases and will also describe the nature of these enzymes, their inhibition and their molecular characteristics. For more extensive reviews about the biological roles of NO, see [5-7].

/pdf/nitric-oxide-synthases-in-mammals-1etyzijagx.pdf

Paul L. Feldman

Papers

N omega-hydroxy-L-arginine is an intermediate in the biosynthesis of nitric oxide from L-arginine.

The surprising life of nitric oxide