Nitric-oxide synthase

NOS catalyses the generation of nitric oxide (nitrogen monoxide, NO) from L-arginine. Three major isoforms occur in mammals neuronal NOS (nNOS or type I) and endothelial NOS (eNOS or type III) require Ca2+ for activity, 

Stuehr and Ikeda-Saitos used EPR and optical spectroscopy to characterize nitric oxide synthases isolated from brain and ey tokine-aetivated maerophages. They found that both enzymes contain two molecules of iron-protoporphyrin IX per protein homodimer and showed that the optieal and EPR speetroscopie 

The genes of the inducible and the constitutively expressed forms of NOS have been cloned and expressed. The expression of inducible NOS in the brain tissue of animals with experimentally induced neurological disorders (boma disease virus and rabies virus in rats), herpes simplex virus (mice) and experimental allergic encephalitis (in rats) suggests that NO produced by induced NOS may be a toxic fector in the pathogenesis of neurological diseases (Koprowski et /., 1993). 

During ischaemia, NOS is activated by calcium influx or by cytokines like tumour necrosis factor (TNF) or by lipopolysaccharide (LPS) and NO is produced in excess. It has been proposed that the excitotoxic effect of glutamate, which contributes to ischaemia-induced neuronal damage, is mediated by increased production of NO via a chain of events that includes increases in intracellular calcium (via glutamate activation of NMDA receptors), calcium activation of NOS, production of NO and peroxynitrite, and induction of lipid peroxidation. In fact, N-nitro-L-atginine, a selective inhibitor of NOS, has been shown to prevent glutamate-induced neurotoxicity in cortical cell cultures (Dawson rf /., 1991). 

N-Nitro-L-arginine methyl ester (L-NAME) is an inhibitor of NOS L-NAME reportedly reduces the volume of cortical and striatal infarct after middle cerebral artery occlusion in the rat. This protection can be reversed by co-injection of L-arginine. L-NAME also reduced the excitotoxic damage induced by NMDA injection. Finally, the authors showed that L-NAME reduced glutamate efflux produced by ischaemic injury in rats. The authors concluded that NOS induced by NMDA receptor overstimulation is a key event in the neuronal injury cascade (Buisson eta/., 1993). 

In contrast to the deleterious effects of arginine described by Buisson, L-arginine was shown to decrease infarct size caused by middle cerebral artery occlusion in spontaneously hypertensive rats. L-Arginine is a precursor for NO synthesis by NOS. The authors attributed the protection to dilation of cerebral blood vessels by NO (Morikawa et 1992). These examples illustrate the difficulty that the NO villain/protector paradox presents to us. 

The NO donor, C87-3754, reportedly attenuates the injury induced in cats by splanchnic artery occlusion of the coeliac, superior mesenteric and inferior mesenteric 

A set of structural and kinetic investigations indicates that the heme active structure of NOS and the mechanism of Arg hydroxylation are similar to those for cytochrome P450 (Bee et al., 1998 Stuehr, 1999 Adak et al., 2001a,b Abu-Saud et al., 2000 Wei et al., 2001 Wolthers, 2002 Lange et al., 2001). The mechanism involves the reduction of 

Recent investigations have shed light on peculiarities of the NOS action mechanism the role of the H4B cofactor and CaM, and cooperativity in kinetic and thermodynamic properties of different components of the nitric oxide synthesis system. Stop flow experiments with eNOS (Abu-Soud et al., 2000) showed that calmodulin binding caused an increase in NADH-dependent flavin reduction from 0.13 to 86 s 1 at 10 °C. Under such conditions, in the presence of Arg, heme is reduced very slowly (0.005 s 1). Heme complex formation requires a relatively high concentration ofNO ( 50 nM) and inhibits the entire process NADH oxidation and citrulline synthesis decreases 3-fold and Km increases 3-fold. NOS reactions were monitored at subzero temperatures in the presence of 50% ethylene glycol as an anti-freeze solvent (Bee et al., 1998). 

At 30°C in the absence of Arg, the ferrous-oxi complex transforms very slowly to the ferric state. In the presence of substrate and H4B, a new species with the 12-nm shifted Sorey band is detected. A decay of this species is accompanied by the formation ofN -hydroxy-L-arginine. Because the presence of HUB is necessary for these reactions, the main function of this compound is to be a reducing agent. This suggestion is supported by experiments on the stabilizing effect of ascorbic acid on the chemical stabilization of tetrahydropterin in the endothelial nitric oxide synthesis (Heller et al., 2001). At the same time, a significant increase in the half lifetime of H4B in solution is demonstrated. As is shown (Wei et al., 2001), a ferrous-dioxy intermediate in iNOS forms for 53 s 1 and then is transformed to the [S-Fe(IV)=0] state. The rate of the [S-Fe(IV)=0] decay is equal to the rate ofH4B radical formation and the rate of Arg hydroxylation. In contrast, 

A 10-step kinetic model has been developed (Santolini et al., 2001). Crystal structures of xyNOS show that a Tyr-409 indol nitrogen atom forms a strong hydrogen bond with the heme thiolate (Crane et al., 1988 Raman et al.1998 Fishmann et al., 1999). The Try-409 mutation suggests that the heme potential controls the NOS reactions (Adak et al. 2001). Suppression of this hydrogen bond through the mutation lowers the reduction potential of the heme, inhibits heme reduction and accelerates oxidation of the Fe(II) heme-NO complex. The Arg binding increases the reduction potential of the NOS heme. 

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Nitric oxides Nitric oxide synthase Nitric oxide synthases Nitrided steels Nitride fibers Nitrides... 

Grb-2 facilitates the transduction of an extracellular stimulus to an intracellular signaling pathway, (b) The adaptor protein PSD-95 associates through one of its three PDZ domains with the N-methyl-D-aspartic acid (NMDA) receptor. Another PDZ domain associates with a PDZ domain from neuronal nitric oxide synthase (nNOS). Through its interaction with PSD-95, nNOS is localized to the NMDA receptor. Stimulation by glutamate induces an influx of calcium, which activates nNOS, resulting in the production of nitric oxide. 

Secretory leukocyte inhibitory protein (SLPI) Inducible nitric oxide synthase (iNOS)... 

Inducible (immunological) Nitric Oxide Synthase Nitric Oxide... 

Three isoforms of NO synthesizing enzymes ( nitric oxide synthase (NOS)) were isolated, purified, and cloned neuronal NO synthase ( neuronal nitric oxide synthase (nNOS) or isoform (I), immunological or inducible NOS ( inducible (immunological) nitric oxide synthase (iNOS) or isoform (II), and endothelial NOS ( endothelial nitric oxide synthase (eNOS) or isoform... 

Kleinert H, Pautz A, Linker K, Schwarz PM (2004) Regulation of the expression of inducible nitric oxide synthase. Eur J Pharmacol 500 255-266... 

Forstermann U (2000) Regulation of nitric oxide synthase expression and activity. In Mayer B (ed) Handbook of experimental pharmacology — nitric oxide, vol. 143. Springer, Berlin, pp 71—91... 

Fleming I, Busse R (2003) Molecular mechanisms involved in the regulation of the endothelial nitric oxide synthase. Am J Physiol 284 R1-12... 

Kleinert H, Boissel J-P, Schwarz PM et al (2000) Regulation of the expression of nitric oxide synthases. In Ignarro LJ (ed) Nitric oxide, biology and pathobiology. Academic Press, San Diego, CA, pp 105-128... 

Endothelial Nitric Oxide Synthase (eNOS) Endothelin Converting Enzyme Endothelins Endothelium... 

Collins SE, Kantak KM Neuronal nitric oxide synthase inhibition decreases cocaine self-administration behavior in rats. Psychopharmacology (Berl) 159 361-369,... 

Scarei S., Giovine M., Gasparini A., Damonte G., Millo E., Pozzolini M., Benatti U. Modified peptide nucleic acids are internalized in mouse macrophages RAW 264.7 and inhibit inducible nitric oxide synthase. FEB. S. Lett. 1999 451 264-268. 

While the fluid mosaic model of membrane stmcture has stood up well to detailed scrutiny, additional features of membrane structure and function are constantly emerging. Two structures of particular current interest, located in surface membranes, are tipid rafts and caveolae. The former are dynamic areas of the exo-plasmic leaflet of the lipid bilayer enriched in cholesterol and sphingolipids they are involved in signal transduction and possibly other processes. Caveolae may derive from lipid rafts. Many if not all of them contain the protein caveolin-1, which may be involved in their formation from rafts. Caveolae are observable by electron microscopy as flask-shaped indentations of the cell membrane. Proteins detected in caveolae include various components of the signal-transduction system (eg, the insutin receptor and some G proteins), the folate receptor, and endothetial nitric oxide synthase (eNOS). Caveolae and lipid rafts are active areas of research, and ideas concerning them and their possible roles in various diseases are rapidly evolving. 

Zhu Y, Jones G et al (2005) Lentivirus infection causes neuroinflammation and neuronal injury in dorsal root ganglia pathogenic effects of STAT-1 and inducible nitric oxide synthase. J Immunol 175(2) 1118-1126... 

Schaefer U, Schneider A, Rixen D, Neugebauer E (1998) Neutrophil adhesion to histamine stimulated cultured endothelial cells is primarily mediated via activation of phospholipase C and nitric oxide synthase isozymes. Inflamm Res 47(6) 256-264 Schaefer U, Schmitz V, Schneider A, Neugebauer E (1999) Histamine induced homologous and heterologous regulation of histamine receptor subtype mRNA expression in cultured endothelial ceUs. Shock 12(4) 309-315... 

Amin-Hanjani S, StagUano NE, Yamada M, Huang PL, Liao JK, Moskowitz MA. Mevastatin, an HMG-CoA reductase inhibitor, reduces stroke damage and upregulates endotheUal nitric oxide synthase in mice. Stroke 2001 32 980-986. 

Han HS, Qiao Y, Karabiyikoglu M, Giffard RG, Yenari MA. Influence of mild hypothermia on inducible nitric oxide synthase expression and reactive nitrogen production in experimental stroke and inflammation. J Neurosci 2002 22 3921-3928. 

Nitric oxide has also been implicated in PD. Thus animals with MPTP-induced Parkinsonism not only show extensive gliosis in the substantia nigra (like humans) in which the glial cells produce NO, but Liberatore and colleagues have found that in iNOS (inducible nitric oxide synthase) knock-out mice the toxicity of MPTP is halved. Since NO releases iron from ferritin and produces toxic peroxinitrate in the presence of superoxide radicals it could accelerate, even if it does not initiate, dopaminergic cell death (see Hirsch and Hunot 2000 for further details). 

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