Increase in the free radical scavenging activity of ginseng by heat-processing

To investigate whether or not the radical scavenging activity of ginseng is enhanced by heat processing, we evaluated the scavenging effects of white ginseng (WG), red ginseng (RG, steamed ginseng at 98-100 degrees C) and sun ginseng (SG, steamed ginseng at 120 degrees C) on nitric oxide, superoxide (O2-), hydroxyl (*OH) radicals and peroxynitrite (ONOO-). Heat-treated ginseng (RG and SG) showed better O2-, ONOO- and *OH-scavenging activities than WG. In particular, the radical scavenging activities of SG were stronger than those of RG. Furthermore, we evaluated the radical scavenging activities of maltol, salicylic acid, vanillic acid and p-coumaric acid, known as principal antioxidant components of ginseng, in WG, RG and SG, and also investigated their contents. Of the tested compounds, maltol, vanillic acid and p-coumaric acid exhibited ONOO(-)-scavenging activity. In addition, maltol and p-coumaric acid showed strong *OH-scavenging activity. Moreover, the content of maltol was remarkably increased in a temperature-dependent manner by heat processing, implying that maltol was closely related to the radical scavenging activity of heat-processed ginseng. These findings indicate that SG may act as a free radical scavenger and protect against damage caused by oxidative stress related with these radicals.

Peroxynitrite Reductase Activity of Selenoprotein Glutathione Peroxidase: A Computational Study

The peroxynitrite reductase activity of selenoprotein glutathione peroxidase (GPx) has been investigated using density functional theory calculations for peroxynitrite/peroxynitrous acid (ONOO-/ONOOH) substrates through two different "oxidation" and "nitration" pathways. In the oxidation pathway for ONOO-, the oxidation of GPx and the subsequent formation of the selenenic acid (E-Se-OH) occur through a concerted mechanism with an energy barrier of 4.7 (3.7) kcal/mol, which is in good agreement with the computed value of 7.1 kcal/mol for the drug ebselen and the experimentally measured barrier of 8.8 kcal/mol for both ebselen and GPx. For ONOOH, the formation of the E-Se-OH prefers a stepwise mechanism with an overall barrier of 6.9 (11.3) kcal/mol, which is 10.2 (11.2) kcal/mol lower than that for hydrogen peroxide (H2O2), indicating that ONOOH is a more efficient substrate for GPx oxidation. It has been demonstrated that the active site Gln83 residue plays a critical role during the oxidation process, which is consistent with the experimental suggestions. The nitration of GPx by ONOOH produces a nitro (E-Se-NO2) product via either of two different mechanisms, isomerization and direct, having almost the same barrier heights. A comparison between the rate-determining barriers of the oxidation and nitration pathways suggests that the oxidation of GPx by ONOOH is more preferable than its nitration. It was also shown that the rate-determining barriers remain the same, 21.5 (25.5) kcal/mol, in the peroxynitrite reductase and peroxidase activities of GPx.

8-nitroguanine, a product of nitrative DNA damage caused by reactive nitrogen species: formation, occurrence, and implications in inflammation and carcinogenesis

The authors review studies on 8-nitroguanine (8-NO(2)-G) formed by reactions of guanine, guanosine, and 2 - deoxyguanosine, either free or in DNA or RNAwith reactive nitrogen species (RNS) generated from peroxynitrite, the myeloperoxidase-H(2)O(2)-nitrite system, and others. Use of antibodies against 8-NO(2)-G has revealed increased formation of 8-NO(2)-G in various pathological conditions, including RNA virus-induced pneumonia in mice, intrahepatic bile ducts of hamsters infected with the liver fluke Opisthorchis viverrini, and gastric mucosa of patients with Helicobacter pylori-induced gastritis. Immunoreactivity has been found in the cytosol as well as in the nucleus of inflammatory cells and epithelial cells in inflamed tissues, but not in normal tissues. 8- NO(2)-G in DNA is potentially mutagenic, yielding G:C to T:A transversion, possibly through its rapid depurination to form an apurinic site and/or miscoding with adenine. 8-NO(2)-G in RNA may interfere with RNA functions and metabolism. Nitrated guanine nucleosides and nucleotides in the nucleotide pool may contribute to oxidative stress via production of superoxide mediated by various reductases and may disturb or modulate directly various important enzymes such as GTP-binding proteins and cGMP-dependent enzymes. Further studies are warranted to establish the roles of 8-NO(2)-G in various pathophysiological conditions and inflammation-associated cancer.

Peroxynitrite-modified DNA: a better antigen for systemic lupus erythematosus anti-DNA autoantibodies

Native human DNA was modified by ONOO- (peroxynitrite), generated by the synergistic action of sodium nitroprusside [Na2Fe(CN)5NO], an NO donor, and pyrogallol, a superoxide donor. The modifications were analysed by UV absorption characteristics, fluorescence emission transitions, nuclease S1 digestibility and melting-temperature studies. Modified DNA was found to be highly immunogenic, inducing high-titre immunogen-specific antibodies in experimental animals. A maximum of 85% inhibition of the antibody binding was observed in competition ELISA with immunogen as inhibitor. SLE (systemic lupus erythematosus) anti-DNA autoantibodies recognized modified DNA as a better antigen than the native analogue. Modification of native DNA by ONOO-, forming neo-epitopes on the molecule, may be one of the factors for the induction of the autoimmune response seen in SLE.

Spectroscopic Characterization of Peroxynitrous Acid in cis-perp Configurations

This paper presents experimental evidence, supported by two-dimensional theoretical calculations, that HOONO can be observed in cis-perp (cp) configurations in a pulsed supersonic expansion. The spectral properties (transition frequency, rotational constants, and transition type) of OH overtone transitions originating from a state with predominately cp character are predicted theoretically and compared with those associated with a weak feature at 6996.2 cm(-1) observed experimentally using infrared action spectroscopy. This spectral feature is attributed to HOONO in cp configurations based on its vibrational frequency, rotational band contour, and resultant OH product state distribution.

Cytochrome p450 compound I

Cytochrome P450 enzymes (P450s) comprise a large class of enzymes that effect numerous oxidations in nature. The active oxidants in P450s are thought to be iron(IV)-oxo porphyrin radical cations termed Compounds I, and these intermediates have been sought since the discovery of P450s 40 years ago. We report formation of the Compound I derivative of a P450 enzyme by laser flash photolysis oxidation of the corresponding Compound II species, an iron(IV)-oxo neutral porphyrin intermediate. The Compound II derivative in turn was produced by oxidation of the P450 with peroxynitrite, which effected a net one-electron, oxo-transfer reaction to the iron(III) atom of the resting enzyme. For the P450 studied in this work, CYP119 from the thermophile Sulfolobus solfactaricus, the P450 Compound II derivative was stable for seconds at ambient temperature, and the Compound I transient decayed with a lifetime of ca. 200 ms.

Mode of action of poly(vinylpyridine-N-oxide) in preventing silicosis: effective scavenging of carbonate anion radical

Small particles of crystalline silicon dioxide (crystallites) are exceptionally toxic. Inhalation of quartz crystallites causes silicosis, a devastating lung disease afflicting miners, particularly coal and stone workers. Poly(vinylpyridine-N-oxide)s (PVPNOs) have been applied in the prevention and treatment of silicosis, but their mode of action has been obscure. Recently, the sites of inducible *NO synthase activation and of nitrotyrosine formation were associated anatomically with the pathological quartz particle-caused lesions in the lungs. It has been suggested that the *NO formed combines rapidly with O2*- to yield ONOO-, a potential mediator of lung injury following silica exposure. Here, we show that PVPNOs do not react with peroxynitrite but scavenge exceptionally rapidly CO3*- radicals, which are produced in the decomposition of ONOO- in bicarbonate solutions. The rate constant for the reaction of CO3*- with PVPNO was found to be independent of the type and size of PVPNO, i.e., k = (1.9 +/- 0.2) x 10(5) M(-1) s(-1) per monomer. In contrast, the rate constant for the reaction of CO3*- with the small molecule 4-methylpyridine N-oxide did not exceed 1 x 10(4) M(-1) s(-1). The underlying reason for the difference is that, in the dissolved polymeric PVPNOs, the electrostatic repulsion between the N-oxide zwitterions destabilizes them, increasing dramatically their pKa. The protonated N-oxides at physiological pH have abstractable hydrogen atoms and are expected to react rapidly with CO3*-, just as cyclic hydroxylamines do. It is also shown that PVPNO inhibits tyrosine nitration by peroxynitrite at pH 7.6 in the presence of excess of CO2 in a concentration-dependent manner. Hence, binding of PVPNO to the quartz particles and eliminating CO3*- could prevent the killing of macrophages, the associated release of macrophage-recruiting cytokines, and the amplification of the local concentration of *NO by the recruited macrophages. The latter causes necrosis of the macrophage-infiltrated lung tissue and, upon repair of the necrotic lesion, results in the growth of the dysfunctional fibrotic tissue, which is the hallmark of silicosis.

Isorhamnetin glycosides with free radical and ONOO− scavenging activities from the stamens ofNelumbo nucifera

In this study, we isolated two new isorhamnetin glycosides, designated as nelumboroside A (3) and nelumboroside B (4), as well as the previously-characterized isorhamnetin glucoside (1) and isorhamnetin rutinoside (2), from the n-BuOH fraction of Nelumbo nucifera stamens. The structures of the two new compounds were then determined, using chemical and spectroscopic techniques. All isolated isorhamnetin glycosides 1-4 showed marked antioxidant activities in the DPPH, and ONOO- assays.

High-valent iron in chemical and biological oxidations

Various aspects of the reactivity of iron(IV) in chemical and biological systems are reviewed. Accumulated evidence shows that the ferryl species [Fe(IV)O](2+) can be formed under a variety of conditions including those related to the ferrous ion-hydrogen peroxide system known as Fenton's reagent. Early evidence that such a species could hydroxylate typical aliphatic C-H bonds included regioselectivities and stereospecificities for cyclohexanol hydroxylation that could not be accounted for by a freely diffusing hydroxyl radical. Iron(IV) porphyrin complexes are also found in the catalytic cycles of cytochrome P450 and chloroperoxidase. Model oxo-iron(IV) porphyrin complexes have shown reactivity similar to the proposed enzymatic intermediates. Mechanistic studies using mechanistically diagnostic substrates have implicated a radical rebound scenario for aliphatic hydroxylation by cytochrome P450. Likewise, several non-heme diiron hydroxylases, AlkB (Omega-hydroxylase), sMMO (soluble methane monooxygenase), XylM (xylene monooxygenase) and T4moH (toluene monooxygenase) all show clear indications of radical rearranged products indicating that the oxygen rebound pathway is a ubiquitous mechanism for hydrocarbon oxygenation by both heme and non-heme iron enzymes.

Nitroxidation, nitration, and oxidation of a BODIPY fluorophore by RNOS and ROS

BODIPY C11 581/591 (BODIPY11) represents a sensitive probe for quantification of relative antioxidant capacity. However, the mechanism of BODIPY11 fluorescence decay in the presence of reactive oxygen species (ROS) and reactive nitrogen oxide species (RNOS) requires clarification. Azo-initiators provide a continuous source of peroxyl radicals that in simple, aerobic, homogeneous, buffered solution simulate lipid peroxyl radical formation. Inhibition of BODIPY11 fluorescence decay was assayed and quantified for several families of antioxidants, including phenols, NO donors, and thiols. Fluorescence decay of BODIPY11 in these systems demonstrated similar patterns of antioxidant activity to those observed in classical oxygen pressure measurements, and provided a readily applied quantification of antioxidant capacity and mechanistic information, which was analyzed by measurement of induction periods, initial rates, and net oxidation. LC/MS analysis confirmed that peroxyl radical-induced irreversible fluorescence decay of the BODIPY11 fluorophore is due to oxidative cleavage of the activated phenyldiene side chain. The behavior of BODIPY11 towards RNOS was more complex, even in these simple systems. Incubation of BODIPY11 with bolus peroxynitrite or a sydnonimine peroxynitrite source produced a variety of novel products, characterized by LC/MS, derived from oxidative cleavage, nitroxidation, and nitration reactions. The "NO scavenger" PTIO reinforced the antioxidant activity of NO, and inhibited BODIPY11 oxidation induced by the sydnonimine. These observations suggest that BODIPY11 is a well-behaved fluorescence probe for peroxidation and antioxidant studies, but that for study of RNOS even co-application of fluorescence decay with LC/MS measurements requires careful analysis and interpretation.

Interaction with phospholipids modulates alpha-synuclein nitration and lipid-protein adduct formation

Intracellular aggregates of alpha-syn (alpha-synuclein) represent pathoanatomical hallmarks of neurodegenerative disorders (synucleinopathies). The molecular mechanisms underlying alpha-syn aggregation into filamentous inclusions may involve oxidation and nitration of the protein. Whereas the effects of oxidants and nitrating species on soluble alpha-syn have been studied in detail, the effect of these reactive species on alpha-syn associated with lipids is still unknown. In the present paper, we report that alpha-syn bound to small unilamellar liposomes composed of phosphatidylcholine/phosphatidic acid is resistant to oxidation and nitration when compared with soluble alpha-syn. Additionally, increasing concentrations of unsaturated fatty acids diminished the oxidation and nitration of alpha-syn upon exposure to fluxes of peroxynitrite (8-20 microM x min(-1)). To investigate the effect of oxidized lipids on alpha-syn, the protein was incubated with the bifunctional electrophile 4-HNE [4-hydroxy-2(E)-nonenal]. MS analysis showed the formation of three major products corresponding to the native protein and alpha-syn plus one or two 4-HNE molecules. Trypsin digestion of the modified protein followed by peptide 'finger-printing' revealed that 4-HNE modified the peptide E46GVVHGVATVAEK58. Further analysis of the peptides with liquid chromatography-tandem MS identified the modified residue as His50. The data indicate that the association of alpha-syn with biological membranes protects the protein from oxidation and nitration and thus diminishes the formation of protein molecules capable of forming aggregates. However, products of lipid peroxidation can also modify alpha-syn, generating novel protein adducts that could serve as biomarkers for documenting oxidative processes in human as well as animal and cellular models of alpha-syn aggregation and pathology.

Plasmodium falciparum 2-Cys peroxiredoxin reacts with plasmoredoxin and peroxynitrite

Thioredoxin peroxidase 1 (TPx1) of the malarial parasite Plasmodium falciparum is a 2-Cys peroxiredoxin involved in the detoxification of reactive oxygen species and - as shown here - of reactive nitrogen species. As novel electron acceptor of reduced TPx1, we characterised peroxynitrite; the rate constant for ONOO- reduction by the enzyme (1 x 10(6) M(-1) s(-1) at pH 7.4 and 37 degrees C) was determined by stopped-flow measurements. As reducing substrate of TPx1, we identified - aside from thioredoxin - plasmoredoxin; this 22-kDa protein occurs only in malarial parasites. When studying the potential roles of Cys74 and Cys170 of Tpx1 in catalysis, as well as in oligomerisation behaviour, we found that replacement of Cys74 by Ala influenced neither the dimerisation nor enzymatic activity of TPx1. In the C170A mutant, however, the kcat/Km for reduced Trx as a substrate was shown to be approximately 50-fold lower and, in contrast to the wild-type enzyme, covalently linked dimers were not formed. For the catalytic cycle of TPx1, we conclude that oxidation of the peroxidatic Cys50 by the oxidising substrate is followed by the formation of an intermolecular disulfide bond between Cys50 and Cys170' of the second subunit, which is then attacked by an external electron donor such as thioredoxin or plasmoredoxin.

Disulphide formation on mitochondrial protein thiols

A large number of proteins contain free thiols that can be modified by the formation of internal disulphides or by mixed disulphides with low-molecular-mass thiols. The majority of these latter modifications result from the interaction of protein thiols with the endogenous glutathione pool. Protein glutathionylation and disulphide formation are of significance both for defence against oxidative damage and in redox signalling. As mitochondria are central to both oxidative damage and redox signalling within the cell, these modifications of mitochondrial proteins are of particular importance. In the present study, we review the mechanisms and physiological significance of these processes.

Persistent S-nitrosation of complex I and other mitochondrial membrane proteins by S-nitrosothiols but not nitric oxide or peroxynitrite: implications for the interaction of nitric oxide with mitochondria

S-nitrosation of mitochondrial proteins has been proposed to contribute to the pathophysiological interactions of nitric oxide (NO) and its derivatives with mitochondria but has not been shown directly. Furthermore, little is known about the mechanism of formation or the fate of these putative S-nitrosothiols. Here we have determined whether mitochondrial membrane protein thiols can be S-nitrosated on exposure to free NO from 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (DETA-NONOate) by interaction with S-nitrosoglutathione or S-nitroso-N-acetylpenicillamine (SNAP) and by the NO derivative peroxynitrite. S-Nitrosation of protein thiols was measured directly by chemiluminescence detection. S-Nitrosoglutathione and S-nitroso-N-acetylpenicillamine led to extensive protein thiol oxidation, with about 30% of the modified protein thiols persistently S-nitrosated. In contrast, there was no protein thiol oxidation or S-nitrosation on exposure to 3,3-bis (aminoethyl)-1-hydroxy-2-oxo-1-triazene. Peroxynitrite extensively oxidized protein thiols but produced negligible amounts of S-nitrosothiols. Therefore, mitochondrial membrane protein thiols are S-nitrosated by preformed S-nitrosothiols but not by NO or by peroxynitrite. These S-nitrosated protein thiols were readily reduced by glutathione, so S-nitrosation will only persist when the mitochondrial glutathione pool is oxidized. Respiratory chain complex I was S-nitrosated by S-nitrosothiols, consistent with it being an important target for S-nitrosation during nitrosative stress. The S-nitrosation of complex I correlated with a significant loss of activity that was reversed by thiol reductants. S-Nitrosation was also associated with increased superoxide production from complex I. These findings point to a significant role for complex I S-nitrosation and consequent dysfunction during nitrosative stress in disorders such as Parkinson disease and sepsis.

Two Pathways of Carbon Dioxide Catalyzed Oxidative Coupling of Phenol by Peroxynitrite

Carbon dioxide catalyzed oxidative coupling of phenol by peroxynitrite occurs by two pathways distinguished by the isomer ratio of 2,2'- to 4,4'-biphenols. As already established, at neutral pH and moderate phenol concentrations, both biphenols are formed in comparable yields by the coupling of two phenoxyl radicals. However, at high pH and phenol concentration, 2,2'-biphenol is the only identified coupled product, and its formation does not involve phenoxyl radicals. Instead, under these conditions, a previously unreported long-lived (t(1/2) approximately 10 s at pH 10 and 1 mM phenol) diamagnetic intermediate with an absorption maximum at 400 nm is observed. This intermediate is formed from phenolate concomitantly with the decay of peroxynitrite and disappears via reaction with phenol [k = (2.4 +/- 0.1) x 10 M(-)(1) s(-)(1) at pH 10.5] to form 2,2'-biphenol. We also find that para-benzoquinone, previously unreported, is formed in up to 5% yield relative to the initial peroxynitrite concentration. The appearance of an absorption band above 500 nm, which might be due to quinhydrone, indicates that hydroquinone is a likely para-benzoquinone precursor. The dependence of para-benzoquinone yields on pH and phenol concentration suggests that its formation is related to the nonradical pathway of 2,2'-biphenol formation. This novel nonradical pathway of 2,2'-biphenol formation might be relevant to the mechanisms of reaction of phenolic antioxidants with peroxynitrite. The existence of two distinct pathways of biphenol formation implies that, apart from a CO(3)(*)(-)/NO(2)(*) radical pair, another reactive intermediate is formed during the carbon dioxide catalyzed decay of peroxynitrite.

An antioxidative and antiinflammatory agent for potential treatment of osteoarthritis from Ecklonia cava

Osteoarthritis is thought to be induced by the ageing-related loss of homeostatic balance between degeneration and repair mechanism around cartilage tissue in which inflammatory mediators such as reactive oxygen species, cytokines and prostaglandins are prone to over-production under undesirable physiological conditions. Phlorotannins are unique polyphenolic compounds bearing dibenzo-1,4-dioxin skeleton which are not found in terrestrial plants but found only in some brown algal species such as Ecklonia and Eisenia families. Phlorotannin-rich extracts of Ecklonia cava including LAD103 showed significant antioxidant activities such as DPPH radical scavenging, ferric ion reduction, peroxynitrite scavenging, and inhibition of LDL oxidation, indicating their possible antioxidative interference both in onset and downstream consequences of osteoarthritis. LAD103 also showed significant down regulation of PGE2 generation in LPS-treated RAW 246.7 cells, and significant inhibition of human recombinant interleukin-1alpha-induced proteoglycan degradation, indicating its beneficial involvement in pathophysiological consequences of osteoarthritis, the mechanism of which needs further investigation. Since LAD103 showed strong therapeutic potentials in arthritic treatment through several in vitro experiments, it is highly encouraged to perform further mechanistic and efficacy studies.

Protective effects of resveratrol against oxidative/nitrative modifications of plasma proteins and lipids exposed to peroxynitrite

The protective effects of resveratrol (3, 4', 5-trihydroxystilbene; present naturally in different plants) against the oxidative/nitrative damage of human plasma proteins induced by peroxynitrite (ONOO-) were studied and compared with those of deferoxamine (DFO; a natural siderophore isolated from Streptomyces pilosus), which is a typical and well-known antioxidant. We also studied the effect of ONOO- on plasma lipid peroxidation and the role of tested antioxidants in this process. ONOO- at the used concentrations (0.01-1 mM) showed toxicity to human plasma components. Exposure of plasma to ONOO- (0.1 mM) resulted in an increase of the level of carbonyl groups and nitrotyrosine residues in plasma proteins (approximately 4-fold and 76-fold, respectively) and in a distinct augmentation of lipid peroxidation (approximately 2-fold). In the presence of 0.1-mM resveratrol, a distinct decrease of carbonyl group formation and tyrosine nitration in plasma proteins caused by 0.1-mM ONOO- was observed (by approximately 70% and 65%, respectively). Addition of 0.1-mM DFO to plasma also distinctly reduced the level of carbonyl groups and nitrotyrosines caused by 0.1-mM ONOO- (by approximately 50% and 60%, respectively). Moreover, these antioxidants also inhibited plasma lipid peroxidation induced by ONOO- (0.1 mM). The obtained results indicate that in vitro resveratrol, like well-known antioxidant DFO, has inhibitory effects on ONOO- -mediated oxidation of proteins and lipids in human plasma.

Coelenterazine (marine bioluminescent substrate): a source of inspiration for the discovery of novel antioxidants

Coelenterazine and derivatives were initially considered in the scientific community for their (bio)luminescent properties. Now, another interest of such hetero-bicycles has been pointed out by the discovery of remarkable antioxidative properties, and an unique mode of action as a "cascade": the mother-compound (imidazolopyrazinone) is transformed by ROS into a daughter-compound (2-amino-pyrazine) also endowed with antioxidative properties. This review illustrates the therapeutic potential of synthetic imidazolopyrazinones (coelenterazine analogues): chemical reactivity assays with singulet oxygen, radical anion superoxide, peroxynitrite, and radicals formed during lipid and LDL peroxidation, cellular tests of protection against oxidative stress using keratinocyte, hepatocyte, neuronal and erythrocyte cells, and finally in vivo evaluation in a hamster model of ischemia-reperfusion, are fully described.

Hypothyroid phenotype is contributed by mitochondrial complex I inactivation due to translocated neuronal nitric-oxide synthase

Although transcriptional effects of thyroid hormones have substantial influence on oxidative metabolism, how thyroid sets basal metabolic rate remains obscure. Compartmental localization of nitric-oxide synthases is important for nitric oxide signaling. We therefore examined liver neuronal nitric-oxide synthase-alpha (nNOS) subcellular distribution as a putative mechanism for thyroid effects on rat metabolic rate. At low 3,3',5-triiodo-L-thyronine levels, nNOS mRNA increased by 3-fold, protein expression by one-fold, and nNOS was selectively translocated to mitochondria without changes in other isoforms. In contrast, under thyroid hormone administration, mRNA level did not change and nNOS remained predominantly localized in cytosol. In hypothyroidism, nNOS translocation resulted in enhanced mitochondrial nitric-oxide synthase activity with low O2 uptake. In this context, NO utilization increased active O2 species and peroxynitrite yields and tyrosine nitration of complex I proteins that reduced complex activity. Hypothyroidism was also associated to high phospho-p38 mitogen-activated protein kinase and decreased phospho-extracellular signal-regulated kinase 1/2 and cyclin D1 levels. Similarly to thyroid hormones, but without changing thyroid status, nitric-oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester increased basal metabolic rate, prevented mitochondrial nitration and complex I derangement, and turned mitogen-activated protein kinase signaling and cyclin D1 expression back to control pattern. We surmise that nNOS spatial confinement in mitochondria is a significant downstream effector of thyroid hormone and hypothyroid phenotype.

Oxidation of hypotaurine and cysteine sulphinic acid by peroxynitrite

Peroxynitrite mediates the oxidation of the sulphinic group of both HTAU (hypotaurine) and CSA (cysteine sulphinic acid), producing the respective sulphonates, TAU (taurine) and CA (cysteic acid). The reaction is associated with extensive oxygen uptake, suggesting that HTAU and CSA are oxidized by the one-electron transfer mechanism to sulphonyl radicals, which may initiate an oxygen-dependent radical chain reaction with the sulphonates as final products. Besides the one-electron mechanism, HTAU and CSA can be oxidized by the two-electron pathway, leading directly to sulphonate formation without oxygen consumption. The apparent second-order rate constants for the direct reaction of peroxynitrite with HTAU and CSA at pH 7.4 and 25 degrees C are 77.4+/-5 and 76.4+/-9 M(-1).s(-1) respectively. For both sulphinates, the apparent second-order rate constants increase sharply with decrease in pH, and the sigmoidal curves obtained are consistent with peroxynitrous acid as the species responsible for sulphinate oxidation. The kinetic data, together with changes in oxygen uptake, sulphinate depletion, sulphonate production, and product distribution of nitrite and nitrate, suggest that oxidation of sulphinates by peroxynitrite may take place by the two reaction pathways whose relative importance depends on reagent concentrations and pH value. In the presence of bicarbonate, the direct reaction of sulphinates with peroxynitrite is inhibited and the oxidative reaction probably involves only the radicals *NO2 and CO3*-, generated by decomposition of the peroxynitrite-CO2 adduct.

Oxyleghemoglobin scavenges nitrogen monoxide and peroxynitrite: a possible role in functioning nodules?

It has been demonstrated that the NO* produced by nitric oxide synthase or by the reduction of nitrite by nitrate reductase plays an important role in plants' defense against microbial pathogens. The detection of nitrosyl Lb in nodules strongly suggests that NO* is also formed in functional nodules. Moreover, NO* may react with superoxide (which has been shown to be produced in nodules by various processes), leading to the formation of peroxynitrite. We have determined the second-order rate constants of the reactions of soybean oxyleghemoglobin with nitrogen monoxide and peroxynitrite. At pH 7.3 and 20 degrees C, the values are on the order of 10(8) and 10(4) M-1 s-1, respectively. In the presence of physiological amounts of CO2 (1.2 mM), the second-order rate constant of the reaction of oxyleghemoglobin peroxynitrite is even larger (10(5) M-1 s-1). The results presented here clearly show that oxyleghemoglobin is able to scavenge any NO* and peroxynitrite formed in functional nodules. This may help to stop NO* triggering a plant defense reaction.

Kinetics and mechanistic studies of the reactions of metleghemoglobin, ferrylleghemoglobin, and nitrosylleghemoglobin with reactive nitrogen species

It is now established that nitrogen monoxide is produced not only in animals but also in plants. However, much less is known about the pathways of generation and the functions of NO. in planta. One of the possible targets of NO. is leghemoglobin (Lb), the hemoprotein found in high concentrations in the root nodules of legumes that establish a symbiosis with nitrogen-fixing bacteria. In analogy to hemoglobin and myoglobin, we have shown that different forms of Lb react not only with NO. but also with so-called reactive nitrogen species derived from it, among others peroxynitrite and nitrite. Because of the wider active-site pocket, the rate constants measured in this work for NO. and for nitrite binding to metLb are 1 order of magnitude larger than the corresponding values for binding of these species to metmyoglobin and methemoglobin. Moreover, we showed that reactive nitrogen species are able to react with two forms of Lb that are produced in vivo but that cannot bind oxygen: ferrylLb is reduced by NO. and nitrite, and nitrosylLb is oxidized by peroxynitrite. The second-order rate constants of these reactions are on the order of 10(2), 10(6), and 10(5) M-1 s-1, respectively. In all cases, the final reaction product is metLb, a further Lb form that has been detected in vivo. Since a specific reductase is active in nodules, which reduces metLb, reactive nitrogen species could contribute to the recycling of these inactive forms to regenerate deoxyLb, the oxygen-binding form of Lb.

Identification of ubiquitin nitration and oxidation using a liquid chromatography/mass selective detector system

Ubiquitin is a member of the family of low-molecular-weight heat shock proteins that serve a vital role in physiological and pathological protein turnover. It appears to be one of the proteins involved in cell alterations during aging, degenerative disorders, and age-related cognitive decline. It is not known exactly how ubiquitin alterations are related to aging disorders; however, it is possible that ubiquitin is one of the target proteins for free-radical attack. In vivo, the free radical superoxide reacts with nitric oxide to form peroxynitrite, a powerful oxidant. Peroxynitrite may react directly with proteins, lipids, and other molecules to cause damage, with ubiquitin being a possible target. In vitro reaction of peroxynitrite with ubiquitin produces two modified forms of the protein, one oxidized at methionine and the other nitrated at tyrosine, which were characterized by electrospray ionization time-of-flight mass spectrometry. The exact location of the nitrated tyrosine residue was determined by in-source collision-induced dissociation using electrospray ionization time-of-flight mass spectrometry.

Quantitation of four guanine oxidation products from reaction of DNA with varying doses of peroxynitrite

The oxidation products obtained from the reaction of peroxynitrite (ONOO-) with dG include-among others-8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), 2,2-diamino-4[(2-deoxy-beta-d-erythro-pentafuranosyl)amino]-5(2H)-oxazolone (oxazolone), spiroiminodihydantoin, and N1-(beta-d-erythro-pentofuranosyl)-5-guanidinohydantoin (guanidinohydantoin). In the present work, the formation of these products from the treatment of calf thymus DNA with varying amounts of ONOO- was studied quantitatively in vitro. 13C-, 15N-labeled standards were synthesized for the nucleosides of interest, and calf thymus DNA was reacted with ONOO- and digested enzymatically down to the nucleoside level. Specific modifications in the DNA were measured by HPLC separation followed by electrospray ionization tandem mass spectrometric analysis in the selected reaction-monitoring mode. Artifacts of the above four oxidation products, arising from oxidation of dG and/or 8-oxodG during DNA digestion and subsequent workup, were evaluated with 7-15N-dG and/or stable-isotope-labeled 8-oxodG as internal standards. Levels of artifactual 8-oxodG were about 5/10(6) nucleosides. The artifacts of spiroiminodihydantoin and guanidinohydantoin, arising from 8-oxodG, were 3.7% and 0.6% of the measured 8-oxodG values, respectively. No artifacts of oxazolone were detected. 8-OxodG and oxazolone were formed dose-dependently in DNA treated with ONOO-, while the levels of spiroiminodihydantoin and guanidinohydantoin increased significantly at low ONOO- doses, and then dropped off at higher ONOO- doses. The complexity of these dose-response relationships is likely due to the dual role of peroxynitrite as both an oxidant and a nucleophile in competition with water.

Nitration of tyrosine 92 mediates the activation of rat microsomal glutathione s-transferase by peroxynitrite

There is increasing evidence that protein function can be modified by nitration of tyrosine residue(s), a reaction catalyzed by proteins with peroxidase activity, or that occurs by interaction with peroxynitrite, a highly reactive oxidant formed by the reaction of nitric oxide with superoxide. Although there are numerous reports describing loss of function after treatment of proteins with peroxynitrite, we recently demonstrated that the microsomal glutathione S-transferase 1 is activated rather than inactivated by peroxynitrite and suggested that this could be attributed to nitration of tyrosine residues rather than to other effects of peroxynitrite. In this report, the nitrated tyrosine residues of peroxynitrite-treated microsomal glutathione S-transferase 1 were characterized by mass spectrometry and their functional significance determined. Of the seven tyrosine residues present in the protein, only those at positions 92 and 153 were nitrated after treatment with peroxynitrite. Three mutants (Y92F, Y153F, and Y92F, Y153F) were created using site-directed mutagenesis and expressed in LLC-PK1 cells. Treatment of the microsomal fractions of these cells with peroxynitrite resulted in an approximately 2-fold increase in enzyme activity in cells expressing the wild type microsomal glutathione S-transferase 1 or the Y153F mutant, whereas the enzyme activity of Y92F and double site mutant was unaffected. These results indicate that activation of microsomal glutathione S-transferase 1 by peroxynitrite is mediated by nitration of tyrosine residue 92 and represents one of the few examples in which a gain in function has been associated with nitration of a specific tyrosine residue.