1,721,004 research outputs found
Enzymatic detoxification of O2 and NO in the human parasite, Giardia intestinalis: A mini review
No full textGiardia intestinalis is the etiological agent of giardiasis, a common human intestinal disease with 280 million cases per year. Giardiasis is typically treated with the broad-range antibiotic metronidazole; however, the emergence of drug-resistant strains calls for the development of new anti-parasitic drugs. Very little is known regarding the molecular mechanisms adopted by Giardia to cope with the oxidative/nitrosative environmental stress, encountered by the parasite during colonization of the human intestine. Giardia is particularly sensitive to oxidative stress, as it lacks some of the most common ROS-detoxifying enzymes and it is endowed with O-2-labile key metabolic enzymes. Surprisingly, it colonizes a fairly aerobic (up to 50 mu M O-2) tract of the human gut (the upper part of the small intestine). Accordingly, survival of the parasite relies on antioxidant systems, though, as yet, the only two H2O-forming and O-2-consuming enzymes described in Giardia are NADH oxidase and flavodiiron protein (FDP). Nitric oxide (NO) is an antimicrobial agent produced, together with ROS, by the host immune system to fight pathogens. In vitro NO-stress has been reported to have cytostatic, rather than cytotoxic, effects on Giardia. This effect leads to the suggestion that Giardia is endowed with defense mechanisms against NO and, very recently, the NO-detoxifying flavohemoglobin from it has been characterized
Antioxidant defence systems in the protozoan pathogen giardia intestinalis
No full textThe microaerophilic protist Giardia intestinalis is the causative agent of giardiasis, one of the most common intestinal infectious diseases worldwide. The pathogen lacks not only respiratory terminal oxidases (being amitochondriate), but also several conventional antioxidant enzymes, including catalase, superoxide dismutase and glutathione peroxidase. In spite of this, since living attached to the mucosa of the proximal small intestine, the parasite should rely on an efficient antioxidant system to survive the oxidative and nitrosative stress conditions found in this tract of the human gut. Here, we review current knowledge on the antioxidant defence systems in G. intestinalis, focusing on the progress made over the last decade in the field. The relevance of this research and future perspectives are discussed
Nitric oxide and cytochrome oxidase: mechanisms of inhibition and NO degradation
No full textNO inhibits mitochondrial respiration by reacting with either the reduced or the oxidized binuclear site of cytochrome c oxidase, leading respectively to accumulation of cytochrome a(3)(2+)-NO or cytochrome a(3)(3+)-NO2- species. Exploiting the unique light sensitivity of the cytochrome a(3)(2+)-NO, we show that under turnover conditions, depending on the cytochrome c(2+) concentration, either the cytochrome a(3)(2+)-NO or the nitrite-bound enzyme is formed. The predominance of one of the two inhibitory pathways depends on the occupancy of the turnover intermediates. In the dark, the respiration recovers at the rate of NO dissociation (k' = 0.01 s(-1) at 37 degrees C). Illumination of the sample speeds up recovery rate only at higher reductant concentrations, indicating that the inhibited species is cytochrome a(3)(2+)-NO. When the reaction occurs with the oxidized binuclear site, light has no effect and NO is oxidized to harmless nitrite eventually released in the bulk, accounting for catalytic NO degradation
Nitric oxide and cytochrome oxidase: Reaction mechanisms from the enzyme to the cell
No full textThe aim of this work is to review the information available on the molecular mechanisms by which the NO radical reversibly downregulates the function of cytochrome c oxidase (CcOX). The mechanisms of the reactions with NO elucidated over the past few years are described and discussed in the context of the inhibitory effects on the enzyme activity. Two alternative reaction pathways are presented whereby NO reacts with the catalytic intermediates of CcOX populated during turnover. The central idea is that at "cellular" concentrations of NO (less than or equal to muM), the redox state of the respiratory chain results in the formation of either the nitrosyl- or the nitrite-derivative of CcOX, with potentially different metabolic implications for the cell. In particular, the role played by CcOX in protecting the cell from excess NO, potentially toxic for mitochondria, is also reviewed highlighting the mechanistic differences between eukaryotes and some prokaryotes. (C) 2003 Elsevier Science Inc
Mitochondria and nitric oxide: chemistry and pathophysiology.
No full textCell respiration is controlled by nitric oxide (NO) reacting with respiratory chain complexes, particularly with Complex I and IV. The functional implication of these reactions is different owing to involvement of different mechanisms. Inhibition of complex IV is rapid (milliseconds) and reversible, and occurs at nanomolar NO concentrations, whereas inhibition of complex I occurs after a prolonged exposure to higher NO concentrations. The inhibition of Complex I involves the reversible S-nitrosation of a key cysteine residue on the ND3 subunit. The reaction of NO with cytochrome c oxidase (CcOX) directly involves the active site of the enzyme: two mechanisms have been described leading to formation of either a relatively stable nitrosyl-derivative (CcOX-NO) or a more labile nitrite-derivative (CcOX-NO 2 - ). Both adducts are inhibited, though with different K I; one mechanism prevails on the other depending on the turnover conditions and availability of substrates, cytochrome c and O 2. SH-SY5Y neuroblastoma cells or lymphoid cells, cultured under standard O 2 tension, proved to follow the mechanism leading to degradation of NO to nitrite. Formation of CcOX-NO occurred upon rising the electron flux level at this site, artificially or in the presence of higher amounts of endogenous reduced cytochrome c. Taken together, the observations suggest that the expression level of mitochondrial cytochrome c may be crucial to determine the respiratory chain NO inhibition pathway prevailing in vivo under nitrosative stress conditions. The putative patho-physiological relevance of the interaction between NO and the respiratory complexes is addressed
Redox properties of the oxygen-detoxifying flavodiiron protein from the human parasite Giardia intestinalis
No full textFlavodiiron proteins (FDPs) are enzymes identified in prokaryotes and a few pathogenic protozoa, which protect microorganisms by reducing O(2) to H(2)O and/or NO to N(2)O. Unlike most prokaryotic FDPs, the protozoan enzymes from the human pathogens Giardia intestinalis and Trichomonas vaginalis are selective towards O(2). UV/vis and EPR spectroscopy showed that, differently from the NO-consuming bacterial FDPs, the Giardia FDP contains an FMN with reduction potentials for the formation of the single and the two-electron reduced forms very close to each other (E(1) = -66 +/- 15 mV and E(2) = -83 +/- 15 mV), a condition favoring destabilization of the semiquinone radical. Giardia FDP contains also a non-heme diiron site with significantly up-shifted reduction potentials (E(1) = +163 20 mV and E(2) = +2 +/- 20 mV). These properties are common to the Trichomonas hydrogenosomal FDP, and likely reflect yet undetermined subtle structural differences in the protozoan FDPs. accounting for their marked O(2) specificity. (C) 2009 Elsevier Inc. All rights reserved
Nitric oxide and the respiratory enzyme
No full textAvailable information on the molecular mechanisms by which nitric oxide (NO) controls the activity of the respiratory enzyme (cytochrome-c-oxidase) is reviewed. We report that, depending on absolute electron flux, NO at physiological concentrations reversibly inhibits cytochrome-c-oxidase by two alternative reaction pathways, yielding either a nitrosyl- or a nitrite-heme a(3) derivative. We address a number of hypotheses, envisaging physiological and/or pathological effects of the reactions between NO and cytochrome-c-oxidase. (c) 2006 Elsevier B.V. All rights reserved
Targeting the antioxidant defense system in the human protozoan parasite Giardia intestinalis
No full textMorphine but not fentanyl and methadone affects mitochondrial membrane potential by inducing NO release in glioma cells.
No full textWe have observed that treatment of human glioma cells with morphine in the nanomolar range of concentration affects the mitochondrial membrane potential. The effect is specific to morphine and is mediated by naloxone-sensitive receptors, and is thus better observed on glioma cells treated with desipramine; moreover, the mitochondrial impairment is not inducible by fentanyl or methadone treatment and is prevented by the nitric oxide (NO) synthase inhibitor L-NAME. We conclude that in cultured glioma cells, the morphine-induced NO release decreases the mitochondrial membrane potential, as one might expect based on the rapid inhibition of the respiratory chain by NO. The identification of new intra-cellular pathways involved in the mechanism of action of morphine opens additional hypotheses, providing a novel rationale relevant to the therapy and toxicology of opioid
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