Nitrite formation from

Hydroperoxide groups react with NO to give only nitrates as the dominant products, with only traces (< 5%) of nitrite in both oxidized polyolefins and in concentrated solutions of model hydroperoxides (-OOH levels from iodometry -ONO and -ON02 levels by IR). As reported by Shelton and Kopczewski we have confirmed that both nitrate and nitrite result from NO reaction with dilute hydroperoxide solutions (24). Rather than the NO-induced 0-0 scission proposed by these authors, our evidence points to hydrogen abstraction by NO (reaction 4). (A similar scheme may explain nitrite formation from alcohols.) Both e.s.r. and FTIR evidence is... 

Hanst, P. L., and E. R. Stephens, Infrared Analysis of Engine Exhausts Methyl Nitrite Formation from Methanol Fuel, Spectroscopy, 4, 33-38 (1989). 

Amarger, N., and Alexander, M. (1968). Nitrite formation from hydroxylamine and oximes by Pseudomonas aeruginosa. ]. Bacteriol. 95, 1651-1657. 

Hoffmann and co-workers [178,179] have studied the photolysis of nitrate and nitrite in both water and water ice over broad temperature ranges. In the case of nitrite formation from nitrate photolysis, the photochemical reaction reaches a steady state condition that can be described by the following rate expression ... 

E2. Elstner, E. F., and Heupel, A., Inhibition of nitrite formation from hydroxylammonium-chlor-ide A simple assay for superoxide dismutase. Anal. Biochem. 70, 616-620 (1976). 

Fig. 3.6. A schematic presentation of nitrite formation from hydroxylamine in the cell of Alcaligenes faecalis. Circled numbers 1, ammonia monooxygenase 2, pyruvic oxime...

Figure 7. Nitrite formation from hydroxylamine. Reaction mixture contained in 3 mL 50 mM phosphate buffer pH 7.8 1 fjjnol of NH OH chloroplasts with 75 /xg of chlorophyll and where indicated 6.6 /aM paraquat 50 units SOD. Illuminated at 275 Wm at 22°C. Key control, plus paraquat. A plus SOD, and plus paraquat and SOD, A (72).

The presence of nitrate as acelerator has a pronounced effect on the amount and composition of gas evolved from the work being treated (Table 15.8). It will be observed that hydrogen evolution drops to a very low figure with the zinc/nitrate baths. The formation of nitrite arises from decomposition of nitrate by reaction with primary ferrous phosphate to form ferric phosphate ... 

Recently nitrosamines have attracted attention because of their marked carcinogenic activity in a wide variety of animal species Q, ). Nitrosamines are likely to be carcinogens in man as well human exposure to these compounds is by ingestion, inhalation, dermal contact and vivo formation from nitrite and amines Nitrite and amines react most rapidly at an acidic pH A variety of factors, however, make nitrosation a potentially important reaction above pH 7 these include the presence of microorganisms, and the possibilities of catalysis by thiocyanate, metals and phenols, and of transnitrosation by other nitroso compounds. 

Ru(edta)(H20)] reacts very rapidly with nitric oxide (171). Reaction is much more rapid at pH 5 than at low and high pHs. The pH/rate profile for this reaction is very similar to those established earlier for reaction of this ruthenium(III) complex with azide and with dimethylthiourea. Such behavior may be interpreted in terms of the protonation equilibria between [Ru(edtaH)(H20)], [Ru(edta)(H20)], and [Ru(edta)(OH)]2- the [Ru(edta)(H20)] species is always the most reactive. The apparent relative slowness of the reaction of [Ru(edta)(H20)] with nitric oxide in acetate buffer is attributable to rapid formation of less reactive [Ru(edta)(OAc)] [Ru(edta)(H20)] also reacts relatively slowly with nitrite. Laser flash photolysis studies of [Ru(edta)(NO)]-show a complicated kinetic pattern, from which it is possible to extract activation parameters both for dissociation of this complex and for its formation from [Ru(edta)(H20)] . Values of AS = —76 J K-1 mol-1 and A V = —12.8 cm3 mol-1 for the latter are compatible with AS values between —76 and —107 J K-1mol-1 and AV values between —7 and —12 cm3 mol-1 for other complex-formation reactions of [Ru(edta) (H20)]- (168) and with an associative mechanism. In contrast, activation parameters for dissociation of [Ru(edta)(NO)] (AS = —4JK-1mol-1 A V = +10 cm3 mol-1) suggest a dissociative interchange mechanism (172). 

Akerboom, T. P. M., Ji, Y., Wagner G., Sies, H., Subunit specificity and organ distribution of glutathione transferase-catalysed S-nitrosoglutathione formation from alkyl nitrites in the rat. Biochem. Phamacol. 53 (1996), p. 117-120... 

Given that hydroxylamine reacts rapidly with heme proteins and other oxidants to produce NO [53], the hydrolysis of hydroxyurea to hydroxylamine also provides an alternative mechanism of NO formation from hydroxyurea, potentially compatible with the observed clinical increases in NO metabolites during hydroxyurea therapy. Incubation of hydroxyurea with human blood in the presence of urease results in the formation of HbNO [122]. This reaction also produces metHb and the NO metabolites nitrite and nitrate and time course studies show that the HbNO forms quickly and reaches a peak after 15 min [122]. Consistent with earlier reports, the incubation ofhy-droxyurea (10 mM) and blood in the absence of urease or with heat-denatured urease fails to produce HbNO over 2 h and suggests that HbNO formation occurs through the reactions of hemoglobin and hydroxylamine, formed by the urease-mediated hydrolysis of hydroxyurea [122]. Significantly, these results confirm that the kinetics of HbNO formation from the direct reactions of hydroxyurea with any blood component occur too slowly to account for the observed in vivo increase in HbNO and focus future work on the hydrolytic metabolism of hydroxyurea. 

Nitrogen uptake that results in the formation of new biomolecules is termed an assimilation process, such as assimilatory nitrogen reduction. The processes that result in the release of DIN into seawater are referred to as dissimilations, such as dissimi-latory nitrogen reduction. An example of the latter is denitrification, in which nitrate and nitrite obtained from seawater serve as electron acceptors to enable the oxidation of organic matter. This causes the nitrate and nitrite to be transformed into reduced species, such as N2O and N2, which are released back into seawater. 

Nitrite formation may lead to nitrous oxide (N O) emission. An example of such a process under reclaimed efQuent disposal on the land surface is reported by Master et al. (2004). Irrigating a grumosol (<60% clay content) with fresh and reclaimed effluent water, it was found that, under efQuent irrigation, the amount of nitrous oxide emissions was double the amount emitted under freshwater treatment, at 60% w/w. The N O emission from efQuent-freated bulk soil was more than double the amount formed from large aggregates. 

Assuming that the above rationale for tertiary amine nitrosation was valid, we predicted 3) that the reaction of secondary amines with nitrite at milder pH s should be catalyzed by electrophilic carbonyl compounds, since secondary amines are known to form immonium ions on admixture with appropriate aldehydes and ketones. The prediction turned out to be true. Formaldehyde was shown to promote nitrosamine formation from a... 

Effects of lL 1/3 and NMMA on islet-cell mitochondrial aconitase activity. Islets were treated for 18 hr with 5 U/ml lL-1, 0.5 mM NMMA, or lL-1/3 and NMMA. The islets were isolated and aconitase activity and the simultaneous release of nitrite were determined as described previously (Corbett et al., 1992b). Treatment of islets with lL-1/3 results in an 80% inhibition of mitochondrial aconitase activity, which is completely prevented by NMMA. lL-1 also stimulates a twofold increase in the level of nitrite released by islets, and NMMA prevents this nitrite formation. Reproduced with permission from J. Clin, Invest. (Corbett et al., 1992b), by the American Society for Clinical Investigation. 

If jS-cell production of nitric oxide participates in IDDM, human islets must produce nitric oxide in response to cytokines. We have shown that a combination of cytokines (lL-1, IFN, and TNF) induce the formation of nitric oxide by isolated human islets (Corbett et al., 1993b). The formation of nitric oxide has been demonstrated by cytokine-induced cGMP accumulation, nitrite formation, and EPR-detectable iron-nitrosyl complex formation (Fig. 12), all of which were prevented by NMMA. The cytokine combination of IFN and lL-1 are required for nitrite production, while TTSIF potentiates IL-1 and IFN-induced nitrite formation by human islets. The cytokine combination of lL-1, TNF, and IFN also influences the physiological function of insulin secretion by human islets. Low concentrations of this cytokine combination slightly stimulate insulin secretion, while high concentrations inhibit insulin secretion, similar to the concentration-dependent effects of lL-1 on rat islet function. NMMA partially prevents the inhibitory effects of this cytokine combination on insulin secretion from human islets, suggesting that nitric oxide may participate in )3-cell dysfunction associated with IDDM. 

F.B. Jensen, Nitric oxide formation from the reaction of nitrite with carp and rabit hemoglobin at intermediate oxygen saturations. FEBS J. 275, 3375-3387 (2008)... 

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