Oxidation of 3-hydroxyanthranilic acid to the phenoxazinone cinnabarinic acid by peroxyl radicals and by compound I of peroxidases or catalase

Since 3-hydroxyanthranilic acid (3HAA), an oxidation product of tryptophan metabolism, is a powerful radical scavenger [Christen, S., Peterhans, E., ; Stocker, R. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 2506], its reaction with peroxyl radicals was investigated further. Exposure to aqueous peroxyl radicals generated at constant rate under air from the thermolabile radical initiator 2,2'-azobis[2-amid-inopropane] hydrochloride (AAPH) resulted in rapid consumption of 3HAA with initial accumulation of its cyclic dimer, cinnabarinic acid (CA). The initial rate of formation of the phenoxazinone CA accounted for approximately 75% of the initial rate of oxidation of 3HAA, taking into account that 2 mol of 3HAA are required to form 1 mol of CA. Consumption of 3HAA under anaerobic conditions (where alkyl radicals are produced from AAPH) was considerably slower and did not result in detectable formation of CA. Addition of superoxide dismutase enhanced autoxidation of 3HAA as well as the initial rates of peroxyl radical-induced oxidation of 3HAA and formation of CA by approximately 40-50%, whereas inclusion of xanthine/xanthine oxidase decreased the rate of oxidation of 3HAA by approximately 50% and inhibited formation of CA almost completely, suggesting that superoxide anion radical (O2.-) was formed and reacted with reaction intermediate(s) to curtail formation of CA. Formation of CA was also observed when 3HAA was added to performed compound I of horseradish peroxidase (HRPO) or catalytic amounts of either HRPO, myeloperoxidase, or bovine liver catalase together with glucose/glucose oxidase.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione peroxidase overexpression causes aberrant ERK activation in neonatal mouse cortex after hypoxic preconditioning

Preconditioning of neonatal mice with nonlethal hypoxia (HPC) protects the brain from hypoxic-ischemic (HI) injury. Overexpression of human glutathione peroxidase 1 (GPx1), which normally protects the developing murine brain from HI injury, reverses HPC protection, suggesting that a certain threshold of hydrogen peroxide concentration is required for activation of HPC signaling.

Hypoxic preconditioning reverses protection after neonatal hypoxia-ischemia in glutathione peroxidase transgenic murine brain

The effect of hypoxic preconditioning (PC) on hypoxic-ischemic (HI) injury was explored in glutathione peroxidase (GPx)-overexpressing mice (human GPx-transgenic [hGPx-tg]) mice. Six-day-old hGPx-tg mice and wild-type (Wt) littermates were pre-conditioned with hypoxia for 30 min and subjected to the Vannucci procedure of HI 24 h after the PC stimulus. Histopathological injury was determined 5 d later (P12). Additional animals were killed 2 h or 24 h after HI and ipsilateral cerebral cortices assayed for GPx activity, glutathione (GSH), and hydrogen peroxide (H2O2). In line with previous studies, hypoxic PC reduced injury in the Wt brain. Preconditioned Wt brain had increased GPx activity, but reduced GSH, relative to naive 24 h after HI. Hypoxic PC did not reduce injury to hGPx-tg brain and even reversed the protection previously reported in the hGPx-tg. GPx activity and GSH in hGPx-tg cortices did not change. Without PC, hGPx-tg cortex had less H2O2 accumulation than Wt at both 2 h and 24 h. With PC, H2O2 remained low in hGPx-tg compared with Wt at 2 h, but at 24 h, there was no longer a difference between hGPx-tg and Wt cortices. Accumulation of H2O2 may be a mediator of injury, but may also induce protective mechanisms.

Post-translational tyrosine nitration of eosinophil granule toxins mediated by eosinophil peroxidase

Nitration of tyrosine residues has been observed during various acute and chronic inflammatory diseases. However, the mechanism of tyrosine nitration and the nature of the proteins that become tyrosine nitrated during inflammation remain unclear. Here we show that eosinophils but not other cell types including neutrophils contain nitrotyrosine-positive proteins in specific granules. Furthermore, we demonstrate that the human eosinophil toxins, eosinophil peroxidase (EPO), major basic protein, eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP), and the respective murine toxins, are post-translationally modified by nitration at tyrosine residues during cell maturation. High resolution affinity-mass spectrometry identified specific single nitration sites at Tyr349 in EPO and Tyr33 in both ECP and EDN. ECP and EDN crystal structures revealed and EPO structure modeling suggested that the nitrated tyrosine residues in the toxins are surface exposed. Studies in EPO(-/-), gp91phox(-/-), and NOS(-/-) mice revealed that tyrosine nitration of these toxins is mediated by EPO in the presence of hydrogen peroxide and minute amounts of NOx. Tyrosine nitration of eosinophil granule toxins occurs during maturation of eosinophils, independent of inflammation. These results provide evidence that post-translational tyrosine nitration is unique to eosinophils.

The response of four winter wheat (Triticum aestivum L.) varieties to field water deficit: leaf anti-oxidative protection and proteolytic activity

Introduction: Drought is one of the most significant factors that limit plant productivity. Oxidative stress is a secondary event in many unfavorable environmental conditions. Intracellular proteases have a role in the metabolism reorganisation and nutrient remobilization under stress. In order to under stand the relative significance of oxidative stress and proteolysis in the yield reduction under drought, four varieties of Triticum aestivum L. with different field drought resistance were examined. Methods: A two-year field experiment was conducted. Analyses were performed on the upper most leaf of control plants and plants under water deficitat the stages most critical for yield reduction under drought (from jointing till milk ripeness). Leaf water deficit and electrolyte leakage, malondyaldehyde level, activities and isoenzymes of superoxide dismutase, catalase and peroxidase, leaf protein content and proteolytic activity were studied. Yield components were analyzed. Results: A general trend of increasing the membrane in stability and accumulation of lipid hydroperoxides was observed with some differences among varieties, especially under drought. The anti-oxidative enzyme activities were progressively enhanced, as well as the azocaseinolytic activities. The leaf protein content decreased under drought at the last phase. Differences among varieties were observed in the parameters under study. They were compared to yield components` reduction under water deprivation.

Biochemical changes in barley plants after excessive supply of copper and manganese

The present study was undertaken to identify changes in some important proteins involved in CO2 fixation (Rubisco, Rubisco activase (RA), Rubisco binding protein (RBP)), NH4+ assimilation (glutamine synthetase (GS) and glutamate synthase (GOGAT)), using immunoblotting, and in the antioxidative defense as a result of Cu or Mn excess in barley leaves (Hordeum vulgare L. cv. Obzor). Activities and isoenzyme patterns of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase (CAT), as well as the levels of ascorbate (ASC), non-protein sulfhydryl groups, hydrogen peroxide and oxidative damage to proteins were determined. Data were correlated to the accumulation of Cu or Mn in the leaves after 5 days supply of heavy metal (HM) excess in the nutrient solution. In the highest Cu excess (1500 μM), Rubisco LS and SS were reduced considerably whereas under the highest Mn concentrations (18,300 μM) only minor changes in Rubisco subunits were detected. The RBP was diminished under the highest concentrations of both Cu or Mn. The bands of RA changed differently comparing Cu and Mn toxicity. GS decreased and GOGAT was absent under the highest concentration of Cu. At Mn excess Fd-GOGAT diminished whereas GS was not apparently changed. The development of toxicity symptoms corresponded to an accumulation of Cu or Mn in the leaves and to a gradual increase in protein carbonylation, a lower SOD activity and elevated CAT and GPX activities. APX activity was diminished under Mn toxicity and was not changed under Cu excess. Generally, changes in the isoenzyme profiles were similar under both toxicities. An accumulation of H2O2 was observed only at Mn excess. Contrasting changes in the low-molecular antioxidants were detected when comparing both toxicities. Cu excess affected mainly the non-protein SH groups, while Mn influenced the ASC content. Oxidative stress under Cu or Mn toxicity was most probably the consequence of depletion in low-molecular antioxidants as a result of their involvement in detoxification processes and disbalance in antioxidative enzymes. The link between heavy metal accumulation in leaves, leading to different display of oxidative stress, and changes in individual chloroplast proteins is discussed in the article.