Catalase catalyzes nitrotyrosine formation from sodium azide and hydrogen peroxide

Sodium azide (NaN₃) is known as an inhibitor of catalase, and a nitric oxide (NO) donor in the presence of catalase and H₂O₂. We showed here that catalase-catalyzed oxidation of NaN₃ can generate reactive nitrogen species which contribute to tyrosine nitration in the presence of H₂O₂. The formation of free-tyrosine nitration and protein-bound tyrosine nitration by the NaN₃/catalase/H₂O₂ system showed a maximum level at pH 6.0. Free-tyrosine nitration induced by peroxynitrite was inhibited by ethanol and dimethyl-sulfoxide (DMSO), and augmented by superoxide dismutase (SOD). However, free-tyrosine nitration induced by the NaN₃/catalase/H₂O₂ system was not affected by ethanol, DMSO and SOD. NO^-₂ and NO donating agents did not affect free-tyrosine nitration by the NaN₃/catalase/H₂O₂ system. The reaction of NaN₃ with hydroxyl radical generating system showed free-tyrosine nitration, but no formation of nitrite and nitrate. The generation of nitrite (NO^-₂) and nitrate (NO^-₃) by the NaN₃/catalase/H₂O₂ system was maximal at pH 5.0. These results suggested that the oxidation of NaN₃ by the catalase/H₂O₂ system generates unknown peroxynitrite-like reactive nitrogen intermediates, which contribute to tyrosine nitration.     

Methylene blue photosensitized oxidation of hypotaurine in the presence of azide generates reactive nitrogen species: formation of nitrotyrosine

In our previous study on the hypotaurine (HTAU) oxidation by methylene blue (MB) photochemically generated singlet oxygen (1O2) we found that azide, usually used as 1O2 quencher, produced, instead, an evident enhancing effect on the oxidation rate [L. Pecci, M. Costa, G. Montefoschi, A. Antonucci, D. Cavallini, Biochem. Biophys. Res. Commun. 254 (1999) 661-665]. We show here that this effect is strongly dependent on pH, with a maximum at approximately pH 5.7. When the MB photochemical system containing HTAU and azide was performed in the presence of tyrosine, 3-nitrotyrosine was produced with maximum yield at pH 5.7, suggesting that azide, by the combined action of HTAU and singlet oxygen, generates nitrogen species which contribute to tyrosine nitration. In addition to HTAU, cysteine sulfinic acid, and sulfite were found to induce the formation of 3-nitrotyrosine. No detectable tyrosine nitration was observed using taurine, the oxidation product of HTAU, or thiol compounds such as cysteine and glutathione. It is shown that during the MB photooxidation of HTAU in the presence of azide, nitrite, and nitrate are produced. Evidences are presented, indicating that nitrite represents the nitrogen species involved in the production of 3-nitrotyrosine. A possible mechanism accounting for the enhancing effect of azide on the photochemical oxidation of HTAU and the production of nitrogen species is proposed.     

Catalase induction protects Haemonchus contortus against hydrogen peroxide in vitro

The response of Haemonchus contortus to oxidative stress in vitro was examined by measuring catalase activities in adult and L4 stage worms exposed to hydrogen peroxide generated by a glucose/glucose oxidase system. Adult nematodes showed increases of up to 2.3-fold in catalase activity after 42 h exposure to the peroxide. L4 nematodes showed up to 4.6-fold induction. A two-stage dose-response was apparent, with catalase activities increasing as the peroxide levels increased, before a return to control levels at higher peroxide concentrations, most likely reflecting a balance between induction and toxicity of the inducing agent itself. Adult nematodes exposed to low levels of peroxide for 24h (hence, having enhanced catalase activities) showed an ability to tolerate subsequent exposure to toxic levels of the peroxide compared to worms with no pre-exposure. An increase of up to approximately threefold in the LC(50) of the hydrogen peroxide generating system was observed after hydrogen peroxide pre-exposure. This indicates that exposure to low oxidant levels lead to an increase in defensive enzyme activities, which allows the nematode to survive subsequent oxidant threats more effectively. The ability of H contortus to increase its catalase activity may be crucial in allowing it to respond to the production of reactive oxygen species by host phagocytes in vivo.     

Efficient production of androgenic doubled-haploid mutants in barley by the application of sodium azide to anther and microspore cultures

 The aim of this study was to establish a protocol for an efficient production of agronomical and/or physiological mutants from model (cvs. Igri and Cobra) and low-androgenic-responding (cv. Volga) cultivars of barley through the application of a mutagenic agent, sodium azide, to anthers and isolated microspores cultured in vitro. This technology offers the possibilities of screening for recessive mutants in the first generation, selecting for novel genotypes from very large haploid populations, avoiding chimerism and rapidly fixing selected genotypes as fertile true breeding lines. The mutagenic treatment, 10^–3–10^–5 M sodium azide, was applied during the anther induction pre-treatment or immediately after the microspore isolation procedure. Out of 616 M₂ doubled-haploid lines characterised under field conditions, a total of 63 morphological and developmental independent mutant lines were identified. The percentage of M₂ doubled-haploid lines carrying mutations per line analysed was 3.8% when 10^–4 M sodium azide was applied to anthers from the low-responding cv. Volga; this increased to 8.6% and 15.6% when 10^–5 and 10^–4 M sodium azide were applied to freshly isolated microspores from model cultivars. Received: 18 April 2000 / Revision received: 28 September 2000 / Accepted: 28 September 2000     

Effects of sodium azide and trifluoperazine on growth,development and monolayer cell differentiation inDictyostelium discoideum

The effects of sodium azide and trifluoperazine on growth, cAMP-chemotaxis, morphogenesis and cell differentiation in the slime mouldDictyostelium discoideum were examined. Growth rate of cells pretreated with low chemical concentrations was reduced directly after the treatment but was partially recovered within two to three hours. The levels of growth inhibition were directly proportional to the chemical concentrations. Low concentrations of trifluoperazine (1 μM) had no clear effect on the morphogenesis of the wild type strain HM27, but induced partial phenotype correction in the final fruiting body of the sporogenous mutant HM28. On the other hand, all relatively non toxic treatments with sodium azide had no effect on morphogenesis of both strains and on cell differentiation of the wild type strain HM27. Both trifluoperazine and sodium azide shifted cell differentiation of the sporogenous mutant HM28 in monolayers from spore- to stalk-pathway. Higher concentrations of both chemicals inhibited cell differentiation in all strains completely. The results indicated that these chemicals influenced the effects of the sporogenous locus which plays a role in the spore/stalk determination mechanism in the sporogenous mutant HM28.     

Asbestos catalyzes hydroxyl and superoxide radical generation from hydrogen peroxide

To understand chemical characteristics of the asbestos minerals which might contribute to tissue damage, the catalytic properties of three different varieties were studied. Using spin trapping techniques it was determined that crocidolite, chrysotile, and amosite asbestos were all able to catalyze the generation of toxic hydroxyl radicals from a normal byproduct of tissue metabolism, hydrogen peroxide. The iron chelator desferroxamine inhibits this reaction, indicating a major role for iron in the catalytic process, and suggesting a possible mechanism by which asbestos toxicity might be reduced.     

Possible involvement of NO-mediated oxidative stress in induction of rat forestomach damage and cell proliferation by combined treatment with catechol and sodium nitrite

To clarify the mechanisms underlying forestomach carcinogenesis in rats by co-treatment with catechol and sodium nitrite (NaNO2), we investigated the involvement of oxidative stress resulting from reaction of the two compounds. Since generation of semiquinone radical, hydroxyl radical (*OH), and peroxynitrite (ONOO-) arose through the reaction of catechol with NO, we proposed that superoxide resulting from catechol oxidation reacted with excess NO, consequently yielding *OH via ONOO-. Male F344 rats were co-treated with 0.2% catechol in the diet and 0.8% NaNO2 in the drinking water for 2 weeks. Prior to occurrence of histological evidence indicating epithelial injury and hyperplasia, 8-hydroxydeoxyguanosine levels in forestomach epithelium significantly increased from 12 h together with appearance of immunohistochemically nitrotyrosine-positive epithelial cells. There were no remarkable changes in rats given each chemical alone. We conclude that oxidative stress due to NO plays an important role in induction of forestomach epithelial damage, cell proliferation, and thus presumably forestomach carcinogenesis.     

AXanthomonas maltophilia isolate tolerating up to 1% sodium azide in Tris/HCl buffer

A bacterium tolerating up to 1% NaN₃ found as a contaminant of Sephadex colums being run with Tris/HCl buffer, was identified asXanthomonas maltophilia. It had low nutrient requirements, was strongly proteolytic and interfered with Sephadex columns run with Tris/HCl buffers.The authors are with the Department of Plant Pathology, Swedish University of Agricultural Sciences, Box 7044, S-750 07 Uppsala, Sweden;     

Peroxynitrite irreversibly decreases diastolic and systolic function in cardiac muscle

Much of the damaging action of nitric oxide in heart may be due to its diffusion-limited reaction with superoxide to form peroxynitrite. Direct infusion of peroxynitrite into isolated perfused hearts fails to model the effects of in situ formation because the bulk of peroxynitrite decomposes before reaching the myocytes. To examine the direct effects of peroxynitrite on the contractile apparatus of the heart, we exposed intact and skinned rat papillary muscles to a steady state concentration of 4-microM peroxynitrite for 5 min, followed by a 30-min recovery period to monitor irreversible effects. In intact muscles developed force fell immediately to 26% of initial force, recovering to 43% by 30 min. Resting tension increased by 600% immediately, and was still elevated 500% by 30 min. Nitrotyrosine immunochemistry showed that peroxynitrite can induce tyrosine nitration at low concentrations and is capable of penetrating 200-380 microm into the papillary muscle after a 5-min infusion. Decomposed peroxynitrite had no effect on either intact or skinned muscle developed force or resting tension. Our results show that peroxynitrite directly damages both developed force and resting tension of isolated heart muscle, which can be extrapolated to systolic and diastolic injury in intact hearts.     

Soy protein diet ameliorates renal nitrotyrosine formation and chronic nephropathy induced by puromycin aminonucleoside

It has been shown that reactive oxygen species are involved in chronic puromycin aminonucleoside (PAN) induced nephrotic syndrome (NS) and that a 20% soy protein diet reduces renal damage in this experimental model. The purpose of the present work was to investigate if a 20% soy protein diet is able to modulate kidney nitrotyrosine formation and the activity of renal antioxidant enzymes (catalase, glutathione peroxidase, Cu,Zn- or Mn-superoxide dismutase) which could explain, at least in part, the protective effect of the soy protein diet in rats with chronic NS induced by PAN. Four groups of rats were studied: (1) Control rats fed 20% casein diet, (2) Nephrotic rats fed 20% casein diet, (3) Control rats fed 20% soy protein diet, and (4) Nephrotic rats fed 20% soy protein diet. Chronic NS was induced by repeated injections of PAN and rats were sacrificed at week nine. The soy protein diet ameliorated proteinuria, hypercholesterolemia, and the increase in serum creatinine and blood urea nitrogen observed in nephrotic rats fed 20% casein diet. Kidney nitrotyrosine formation increased in nephrotic rats fed 20% casein diet and this increase was ameliorated in nephrotic rats fed 20% soy protein diet. However, the soy protein diet was unable to modulate the antioxidant enzymes activities in control and nephrotic rats fed 20% soy protein diet. Food intake was similar in the two diet groups. The protective effect of a 20% soy protein diet on renal damage in chronic nephropathy induced by PAN was associated with the amelioration in the renal nitrotyrosine formation but not with the modulation of antioxidant enzymes.     

Photo-irradiated titanium dioxide catalyzes site specific DNA damage via generation of hydrogen peroxide

Titanium dioxide (TiO₂) is a potential photosensitizer for photodynamic therapy. In this study, the mechanism of DNA damage catalyzed by photo-irradiated TiO₂ was examined using [₃₂P]-5'-end-labeled DNA fragments obtained from human genes. Photo-irradiated TiO₂ (anatase and rutile) caused DNA cleavage frequently at the guanine residue in the presence of Cu(II) after E. coli formamidopyrimidine-DNA glycosylase treatment, and the thymine residue was also cleaved after piperidine treatment. Catalase, SOD and bathocuproine, a chelator of Cu(I), inhibited the DNA damage, suggesting the involvement of hydrogen peroxide, superoxide and Cu(I). The photocatalytic generation of Cu(I) from Cu(II) was decreased by the addition of SOD. These findings suggest that the inhibitory effect of SOD on DNA damage is due to the inhibition of the reduction of Cu(II) by superoxide. We also measured the formation of 8-oxo-7,8-dihydro-2' -deoxyguanosine, an indicator of oxidative DNA damage, and showed that anatase is more active than rutile. On the other hand, high concentration of anatase caused DNA damage in the absence of Cu(II). Typical free hydroxyl radical scavengers, such as ethanol, mannnitol, sodium formate and DMSO, inhibited the copper-independent DNA photodamage by anatase. In conclusion, photo-irradiated TiO₂ particles catalyze the copper-mediated site-specific DNA damage via the formation of hydrogen peroxide rather than that of a free hydroxyl radical. This DNA-damaging mechanism may participate in the phototoxicity of TiO₂.     

The mechanisms for nitration and nitrotyrosine formation in vitro and in vivo: Impact of diet

The detection of 3-nitro-L-tyrosine residues associated with many disease states, including gastric cancer, has implicated a role for peroxynitrite in vivo, and thus endogenously produced nitric oxide and superoxide. Additionally, dietary nitrate has been suggested to be involved in the pathogenesis of gastric cancer through a mechanism involving reduction to nitrite and subsequent formation of potentially mutagenic nitrosocompounds. Studies have now demonstrated that a multitude of reactive nitrogen species other than peroxynitrite are capable of producing nitrotyrosine. Thus, we have reviewed the evidence that dietary nitrate, amongst other reactive nitrogen species, may contribute to the body burden of nitrotyrosine.     

Antioxidant action of sodium diethyldithiocarbamate: Reaction with hydrogen peroxide and superoxide radical

The oxidation of sodium diethyldithiocarbamate (DDC) by hydrogen peroxide or superoxide radicals has been investigated. Hydrogen peroxide oxidizes DDC, leading to the formation of a hydrated form of disulfiram, a dimer of DDC having a disulfide group. In equimolar conditions, the overall process appears as a first-order reaction (k = 0.025±0.005 s⁻¹), the first step being a second-order reaction (k = 5.0±0.1mol⁻¹.1. s⁻¹). No radical intermediate was observed in this process. In the presence of an excess of any of the reagents, the hydrated form of disulfiram transforms into different products corresponding to the fixation of oxygen by sulfur atoms or replacement of C = S group by ketone function, in the presence of an excess of hydrogen peroxide. Superoxide anions (produced by steady-state ⁶⁰Co γ-radiolysis) oxidize DDC, yielding similar products to those obtained with hydrogen peroxide with a maximum oxidation G-value of 0.3 μmol.J⁻¹. The rate constant k(O₂^·− + DDC) is equal to 900 mol⁻¹. 1. s⁻¹.     

The mechanism of oxyperoxidase formation from ferryl peroxidase and hydrogen peroxide

Formation of oxyperoxidase from the reaction of ferryl horseradish peroxidase with H2O2 is inhibited by a small amount of tetranitromethane (TNM), a powerful scavenger of superoxide anion radical. The inhibition by TNM, however, does not exceed 35% as the TNM concentration is increased above 5 microM. The stoichiometry of the reaction in the presence of TNM suggests the following equation for TNM-sensitive formation of oxyperoxidase. Ferryl peroxidase + H2O2----(ferric peroxidase + O2- + H+)----oxyperoxidase The kinetic study on the TNM-resistant formation of oxyperoxidase suggests that the displacement of the oxygen with H2O2 takes place at the sixth coordination position at maximal rates of 0.048 and 0.054 s-1 for peroxidases A and C, respectively, at 5 degrees C. The TNM-sensitive and -resistant reactions are concluded to occur in parallel, and both yield oxyperoxidase. In either mechanism, the protonated form of ferryl peroxidase is active and the pK alpha value is 7.1 for peroxidase A and 8.6 for peroxidase C. Oxyperoxidase decomposes spontaneously with a large activation energy (23.0 kcal/mol), and the reaction of ferryl peroxidase with H2O2 reaches a steady level of oxyperoxidase, which depends on pH and the concentration of H2O2.     

Tryparedoxin peroxidases from Trypanosoma cruzi: high efficiency in the catalytic elimination of hydrogen peroxide and peroxynitrite

During host cell infection, Trypanosoma cruzi parasites are exposed to reactive oxygen and nitrogen species. As part of their antioxidant defense systems, they express two tryparedoxin peroxidases (TXNPx), thiol-dependent peroxidases members of the peroxiredoxin family. In this work, we report a kinetic characterization of cytosolic (c-TXNPx) and mitochondrial (m-TXNPx) tryparedoxin peroxidases from T. cruzi. Both c-TXNPx and m-TXNPx rapidly reduced hydrogen peroxide (k = 3.0 × 10⁷ and 6 × 10⁶ M⁻¹ s⁻¹ at pH 7.4 and 25 °C, respectively) and peroxynitrite (k = 1.0 × 10⁶ and k = 1.8 × 10⁷ M⁻¹ s⁻¹ at pH 7.4 and 25 °C, respectively). The reductive part of the catalytic cycle was also studied, and the rate constant for the reduction of c-TXNPx by tryparedoxin I was 1.3 × 10⁶ M⁻¹ s⁻¹. The catalytic role of two conserved cysteine residues in both TXNPxs was confirmed with the identification of Cys52 and Cys173 (in c-TXNPX) and Cys81 and Cys204 (in m-TXNPx) as the peroxidatic and resolving cysteines, respectively. Our results indicate that mitochondrial and cytosolic TXNPxs from T. cruzi are highly efficient peroxidases that reduce hydrogen peroxide and peroxynitrite, and contribute to the understanding of their role as virulence factors reported in vivo.     

青岛文昌鱼过氧化氢酶基因的克隆及生物信息学分析

过氧化氢酶(catalase,CAT)是一类广泛存在于动物、植物和微生物体内的末端氧化酶,是生物体内抗氧化酶体系的重要成员,因此本研究旨在克隆文昌鱼CAT基因并对其进行生物信息学分析。本研究以青岛文昌鱼(Branchiostoma belcheri tsingtauense)为材料,用RACE技术首次克隆了其CAT全长cDNA的基因序列,命名为AmphiCAT(GenBank登录号:KU058636);该序列总长为2640 bp,开放阅读框(open reading frame,ORF)为1533 bp,编码510个氨基酸,含有一个长为19个氨基酸序列的潜在活性位点和一个长为9个氨基酸序列的血红素配体信号,总分子量在线预测约为57.85 kD;经生物软件分析确定该蛋白质无信号肽序列,预测该蛋白质为非分泌性蛋白,属于单功能CAT的clade3分支;该基因的分子进化树表明青岛文昌鱼CAT同软体动物的亲缘关系较近。     

Nitroproteins from a human pituitary adenoma tissue discovered with a nitrotyrosine affinity column and tandem mass spectrometry

The aim of this study was to characterize endogenous nitroproteins, and those proteins that interact with nitroproteins, in a human pituitary nonfunctional adenoma so as to clarify the role of protein nitration in adenomas. A nitrotyrosine affinity column (NTAC) was used to preferentially enrich and isolate endogenous nitroproteins and nitroprotein-protein complexes from a tissue homogenate that was prepared from a human pituitary nonfunctional pituitary adenoma. The preferentially enriched endogenous nitroproteins and nitroprotein-protein complexes were subjected to trypsin digestion, desalination, and tandem mass spectrometry analysis. Nine nitroproteins (Rho-GTPase-activing protein 5, leukocyte immunoglobulin-like receptor subfamily A member 4 precursor, zinc finger protein 432, cAMP-dependent protein kinase type I-beta regulatory subunit, sphingosine-1-phosphate lyase 1, centaurin beta 1, proteasome subunit alpha type 2, interleukin 1 family member 6, and rhophilin 2) and three proteins (interleukin 1 receptor-associated kinase-like 2, glutamate receptor-interacting protein 2, and ubiquitin) that interacted with nitroproteins were discovered. The nitration site of each nitroprotein was located onto the functional domain where nitration occurred, and each nitroprotein was related to a corresponding functional system. Those data indicate that protein nitration might be an important molecular event in the formation of a human pituitary nonfunctional adenoma.     

猪肝产过氧化氢酶后之废渣酶法生产复合氨基酸工艺研究

本文对以猪肝为原料生产过氧化氢酶过程中产生的废渣、废水进行了深入处理,采用胃蛋白酶进行酶解后提取出一种富含氨基酸和多种营养成分的物质——复合氨基酸粉,并实现了废渣废水零排放的清洁生产工艺。并对胃蛋白酶酶解废渣、废水的条件进行了优化,得到最佳酶解条件为:酶解温度35℃,pH 2,酶解时间12 h。