Role of Superoxide Anions in the Redox Changes Affecting the Physiologically Occurring Cu(I)-Glutathione Complex (original) (raw)
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Cu(I)–Glutathione complex: A potential source of superoxide radicals generation
Bioorganic & Medicinal Chemistry, 2008
Cu 2+ ions and GSH molecules interact to swiftly form the complex Cu(I)-glutathione. We investigated the potential capacity of such complex to reduce molecular oxygen. The addition of SOD to a solution containing Cu(I)-glutathione led to a sustained decline of the basal oxygen level. Such effect was partially reverted by the addition of catalase. The complex was able to induce the reduction of cytochrome c and the oxidation of dyhydroethidium into 2-hydroxyethidium. Both effects were totally blocked by SOD. The ability of the complex to generate superoxide radicals was confirmed by EPR spin-trapping. Cu(I)-glutathione induce no oxidation of fluorescein, a hydroxyl radical-sensitive probe. We conclude that in solutions containing the complex, oxygen is continually reduced into superoxide, and that-in absence of interceptors-the latter radicals are quantitatively re-oxidized into molecular oxygen. We suggest that by functioning as a continuous source of superoxide, the complex could potentially affect a broad range of susceptible biological targets.
Journal of Inorganic Biochemistry, 2016
Binding of copper by reduced glutathione (GSH) is generally seen as a mechanism to lower, if not abolish, the otherwise high electrophilicity and redox activity of its free ions. In recent years, however, this concept has been contradicted by new evidence revealing that, rather than stabilizing free copper ions, its binding to GSH leads to the formation of a Cu(I)-[GSH] 2 complex capable of reducing molecular oxygen into superoxide. It is now understood that, under conditions leading to the removal of such radicals, the Cu(I)-[GSH] 2 complex is readily oxidized into Cu(II)-GSSG. Interestingly, in the presence of a GSH excess, the latter complex is able to regenerate the superoxide-generating capacity of the complex it originated from, opening the possibility that a GSH-dependent interplay exists between the reduced and the oxidized glutathione forms of these copper-complexes. Furthermore, recent evidence obtained from experiments conducted in non-cellular systems and intact mitochondria indicates that the Cu(II)-GSSG complex is also able to function in a catalytic manner as an efficient superoxide dismutating-and catalase-like molecule. Here we review and discuss the most relevant chemical and biological evidence on the formation of the Cu(I)-[GSH] 2 and Cu(II)-GSSG complexes and on the potential redox implications associated with their intracellular occurrence.
Bioorganic & Medicinal Chemistry, 2012
The intracellularly-occurring Cu(I)-glutathione complex (Cu(I)- [GSH] 2 ) has the ability to reduce molecular oxygen into superoxide. Removal of such radicals leads to the irreversible conversion of Cu(I)-[GSH] 2 into the redox-inactive Cu(II)-GSSG complex. The present study addressed the potential of reduced glutathione, ascorbate and superoxide to reductively regenerate Cu(I)-[GSH] 2 from Cu(II)-GSSG, and investigated the redox changes involved in such process. Results show that: (i) among the three tested reductants, only GSH is able to reduce the Cu(II) bound to GSSG; (ii) during the reduction of Cu(II)-GSSG, a Cu(I)-GSSG intermediate would be formed (supported here by Cu(I) and GSSG recovery data and by NMR studies); (iii) when GSH is present in a molar excess equal or greater than 1:3, the reduction of Cu(II)-GSSG into Cu(I)-[GSH] 2 is quantitative and complete. Under such conditions, the Cu(II)-GSSG complex acquires a superoxide-generating capacity which is identical to that seen with the Cu(I)-[GSH] 2 complex. Within cells, the concentrations of GSH are at least 2-to 3-fold order of magnitude higher than those expected for the Cu(II)-GSSG complex. Thus, we postulate that the interaction between GSH and Cu(II)-GSSG could be seen as a potential mechanism to regenerate continuously the Cu(I)-[GSH] 2 complex and thereby affect the ability of the latter to generate superoxide.
Reconstitution of Cu,Zn-superoxide dismutase by the Cu(I).glutathione complex
Journal of Biological Chemistry, 1990
100% reconstitution was obtained with stoichiometric copper at any GSH:copper ratio between 2 and 500. Evidence was obtained for the occurrence of a Cu(I)*GSH-protein intermediate in the reconstitution process. In view of the inability of copper-thionein to reconstitute Cu,Zn-superoxide dismutase and of the detection of copper*GSH complexes in copper-overloaded hepatoma cells (Freedman,
Bioorganic & Medicinal Chemistry, 2011
The intracellularly-occurring Cu(I)-glutathione complex (Cu(I)- [GSH] 2 ) has the ability to reduce molecular oxygen into superoxide radicals (O 2 ÁÀ ). Based on such ability, we addressed the potential of this complex to generate the redox-active Fe 2+ species, during its interaction with free Fe 3+ and with ferritin-bound iron. Results show that: (i) the complex reduces free Fe 3+ through a reaction that totally depends on its O 2 ÁÀ -generating capacity; (ii) during its interaction with ferritin, the complex reduces and subsequently releases iron through a largely (77%) SOD-inhibitable reaction; the remaining fraction is accounted for by a direct effect of GSH molecules contained within the complex. The O 2 ÁÀ -dependent iron-releasing efficiency of the complex was half that of its iron-reducing efficiency; (iii) the ability of the complex to release ferritin-bound iron was increased, concentration-dependently, by the addition of GSH and totally prevented by SOD; (iv) in the presence of added H 2 O 2 , the Fe 2+ ions generated through (i) or (ii) were able to catalyze the generation of hydroxyl radicals. Thus, the present study demonstrates the ability of the Cu(I)-[GSH] 2 complex to generate the redox-active Fe 2+ species and suggest that by favouring the occurrence of superoxide-driven Fenton reactions, its pro-oxidant potential could be increased beyond its initial O 2 ÁÀ -generating capacity.
Letter: Mass spectrometric approach of high pH- and copper-induced glutathione oxidation
European Journal of Mass Spectrometry, 2013
All rights reserved EuropEan Journal of Mass spEctroMEtry living cells use the redox properties of copper ions in numerous physiologic processes, whereas GsH balance and copper homeostasis are functionally linked and involved in cell proliferation. 1,2 there is a considerable amount of oxidized glutathione in living cells, which is selectively stashed in vacuoles. 3 the free cu(II) ion is reduced by GsH with the formation of superoxide radicals and the irreversible conversion of cu(I)-[GsH] into the redox-inactive cu(II)-GssG complex. 4,5 However, the reduced glutathione, ascorbate and superoxide are able to regenerate cu(I)-[GsH] from cu(II)-GssG. 6 Glutathione depletion in neurons and aberrant copper metabolism have been implicated in several neurodegenerative disorders. 7 although the interaction of metal ions with peptides has been studied by EsI-Ms, to our knowledge, little information on the affinity of copper ions for GsH is available. under these circumstances, the already reported in literature complexes cu(I)-[GsH] 2 and cu(II)-GssG could be a target in Ms studies. therefore, the aim of this work was to investigate the effect of free copper ions and alkaline environment on the GsH oxidation and the formation of copper-glutathione complexes. this study showed that it is possible to follow by Ms the equilibrium between reduced and oxidized forms of GsH and that between cu(I)-[GsH] 2 and cu(II)-GssG complexes.