Zinc Is a Potent Inhibitor of Thiol Oxidoreductase Activity and Stimulates Reactive Oxygen Species Production by Lipoamide Dehydrogenase (original) (raw)
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Zinc ions as cytochrome c oxidase inhibitors: two sites of action
Biochemistry (Moscow), 2005
Both mitochondrial and bacterial respiratory chains supply the cell with energy due to the conversion of ener gy released from the oxidation of substrates into trans membrane proton gradient across the coupling mem brane. The electron transfer complexes of the respiratory chain, such as NADH:ubiquinone reductase (complex I), ubiquinol:cytochrome c reductase (complex III, or the complex of cytochromes bc 1 ), and cytochrome c oxidase (COX, complex IV) are the coupling membrane bound multisubunit proteins, which act as redox driven proton pumps translocating protons from the inside of mito chondrion to the outside [1 3].
2007
Recent observations point to the role played by Zn 2؉ as an inducer of neuronal death. Two Zn 2؉ targets have been identified that result in inhibition of mitochondrial respiration: the bc 1 center and, more recently, ␣-ketoglutarate dehydrogenase. Zn 2؉ is also a mediator of oxidative stress, leading to mitochondrial failure, release of apoptotic peptides, and neuronal death. We now present evidence, by means of direct biochemical assays, that Zn 2؉ is imported through the Ca 2؉ uniporter and directly targets major enzymes of energy production (lipoamide dehydrogenase) and antioxidant defense (thioredoxin reductase and glutathione reductase). We demonstrate the following. (a) These matrix enzymes are rapidly inhibited by application of Zn 2؉ to intact mitochondria. (b) Delayed treatment with membrane-impermeable chelators has no effect, indicating rapid transport of biologically relevant quantities of Zn 2؉ into the matrix. (c) Membrane-permeable chelators stop but do not reverse enzyme inactivation. (d) Enzyme inhibition is rapid and irreversible and precedes the major changes associated with the mitochondrial permeability transition (MPT). (e) The extent and rate of enzyme inactivation linearly correlates with the MPT onset and propagation. (f) The Ca 2؉ uniporter blocker, Ruthenium Red, protects enzyme activities and delays pore opening up to 2 M Zn 2؉. An additional, unidentified import route functions at higher Zn 2؉ concentrations. (g) No enzyme inactivation is observed for Ca 2؉-induced MPT. These observations strongly suggest that, unlike Ca 2؉ , exogenous Zn 2؉ interferes with mitochondrial NADH production and directly alters redox protection in the matrix, contributing to mitochondrial dysfunction. Inactivation of these enzymes by Zn 2؉ is irreversible, and thus only their de novo synthesis can restore function, which may underlie persistent loss of oxidative carbohydrate metabolism following transient ischemia.
Applied Organometallic Chemistry, 2003
The interactions of zinc pyrithione (ZnPT) with rat liver mitochondria were investigated. Since most of the organometals, principally the triorganotin compounds, induce the inhibition of ATP synthesis in rat liver mitochondria, the efficiency of the ATP synthesis was measured in the presence of ZnPT. The results indicate that ZnPT inhibits ATP synthesis. In order to individuate the molecular mechanism responsible for a failure in ATP synthesis, all of the steps involved in ATP synthesis or in its inhibition were investigated separately, i.e. the respiratory chain, the uncoupling effect, the ATPase and the opening of a permeability pore. All of the steps are inhibited by ZnPT, but the crucial one, the one responsible for the inhibition of ATP synthesis, seems to be the opening of a small-size cyclosporine-sensitive pore. The results are different from those obtained using other organometallic compounds, but are similar to those obtained when using methylmercury and Zn 2+ , both of which also induce the opening of a cyclosporine-sensitive pore. However, although Hg 2+ and Zn 2+ would seem to induce the opening of large-size pores, in the case of ZnPT the pores involved are of a small size. This action mechanism seems to exclude the possibility that ZnPT is a deliverer of Zn 2+ .
2000
Intracellular free Zn 2؉ is elevated in a variety of pathological conditions, including ischemia-reperfusion injury and Alzheimer's disease. Impairment of mitochondrial respiration is also associated with these pathological conditions. To test whether elevated Zn 2؉ and impaired respiration might be linked, respiration of isolated rat liver mitochondria was measured after addition of Zn 2؉. Zn 2؉ inhibition (K i app ؍ ϳ1 M) was observed for respiration stimulated by ␣-ketoglutarate at concentrations well within the range of intracellular Zn 2؉ reported for cultured hepatocytes. The bc 1 complex is inhibited by Zn 2؉ (Link, T. A., and von Jagow, G. (1995) J. Biol. Chem. 270, 25001-25006). However, respiration stimulated by succinate (K i app ؍ ϳ6 M) was less sensitive to Zn 2؉ , indicating the existence of a mitochondrial target for Zn 2؉ upstream from bc 1 complex. Purified pig heart ␣-ketoglutarate dehydrogenase complex was strongly inhibited by Zn 2؉ (K i app ؍ 0.37 ؎ 0.05 M). Glutamate dehydrogenase was more resistant (K i app ؍ 6 M), malate dehydrogenase was unaffected, and succinate dehydrogenase was stimulated by Zn 2؉. Zn 2؉ inhibition of ␣-ketoglutarate dehydrogenase complex required enzyme cycling and was reversed by EDTA. Reversibility was inversely related to the duration of exposure and the concentration of Zn 2؉. Physiological free Zn 2؉ may modulate hepatic mitochondrial respiration by reversible inhibition of the ␣-ketoglutarate dehydrogenase complex. In contrast, extreme or chronic elevation of intracellular Zn 2؉ could contribute to persistent reductions in mitochondrial respiration that have been observed in Zn 2؉-rich diseased tissues.
Journal of Biological Chemistry, 2000
Intracellular free Zn 2؉ is elevated in a variety of pathological conditions, including ischemia-reperfusion injury and Alzheimer's disease. Impairment of mitochondrial respiration is also associated with these pathological conditions. To test whether elevated Zn 2؉ and impaired respiration might be linked, respiration of isolated rat liver mitochondria was measured after addition of Zn 2؉ . Zn 2؉ inhibition (K i app ؍ ϳ1 M) was observed for respiration stimulated by ␣-ketoglutarate at concentrations well within the range of intracellular Zn 2؉ reported for cultured hepatocytes. The bc 1 complex is inhibited by Zn 2؉ (Link, T. A., and von Jagow, G. (1995) J. Biol. Chem. 270, 25001-25006). However, respiration stimulated by succinate (K i app ؍ ϳ6 M) was less sensitive to Zn 2؉ , indicating the existence of a mitochondrial target for Zn 2؉ upstream from bc 1 complex. Purified pig heart ␣-ketoglutarate dehydrogenase complex was strongly inhibited by Zn 2؉ (K i app ؍ 0.37 ؎ 0.05 M). Glutamate dehydrogenase was more resistant (K i app ؍ 6 M), malate dehydrogenase was unaffected, and succinate dehydrogenase was stimulated by Zn 2؉ . Zn 2؉ inhibition of ␣-ketoglutarate dehydrogenase complex required enzyme cycling and was reversed by EDTA. Reversibility was inversely related to the duration of exposure and the concentration of Zn 2؉ . Physiological free Zn 2؉ may modulate hepatic mitochondrial respiration by reversible inhibition of the ␣-ketoglutarate dehydrogenase complex. In contrast, extreme or chronic elevation of intracellular Zn 2؉ could contribute to persistent reductions in mitochondrial respiration that have been observed in Zn 2؉ -rich diseased tissues.
Thionein/metallothionein control Zn (II) availability and the activity of enzymes
Journal of Biological Inorganic Chemistry, 2008
Fundamental issues in zinc biology are how proteins control the concentrations of free Zn(II) ions and how tightly they interact with them. Since, basically, the Zn(II) stability constants of only two cytosolic zinc enzymes, carbonic anhydrase and superoxide dismutase, have been reported, the affinity for Zn(II) of another zinc enzyme, sorbitol dehydrogenase (SDH), was determined. Its log K is 11.2 ± 0.1, which is similar to the log K values of carbonic anhydrase and superoxide dismutase despite considerable differences in the coordination environments of Zn(II) in these enzymes. Protein tyrosine phosphatase 1B (PTP 1B), on the other hand, is not classified as a zinc enzyme but is strongly inhibited by Zn(II), with log K = 7.8 ± 0.1. In order to test whether or not metallothionein (MT) can serve as a source for Zn(II) ions, it was used to control free Zn(II) ion concentrations. MT makes Zn(II) available for both PTP 1B and the apoform of SDH. However, whether or not Zn(II) ions are indeed available for interaction with these enzymes depends on the thionein (T) to MT ratio and the redox poise. At ratios [T/(MT + T) = 0.08-0.31] prevailing in tissues and cells, picomolar concentrations of free Zn(II) are available from MT for reconstituting apoenzymes with Zn(II). Under conditions of decreased ratios, nanomolar concentrations of free Zn(II) become available and affect enzymes that are not zinc metalloenzymes. The match between the Zn(II) buffering capacity of MT and the Zn(II) affinity of proteins suggests a function of MT in controlling cellular Zn(II) availability.
Inorganic Chemistry, 2011
ZincÀthiolate complexes play a major structural and functional role in the living cell. Their stability is directly related to the thiolate reactivity toward reactive oxygen species naturally present in the cell. Oxidation of some zincÀthiolate complexes has a functional role, as is the case of zinc finger redox switches. Herein, we report a theoretical investigation on the oxidation of thiolate by hydrogen peroxide in zinc finger cores of CCCC, CCHC, and CCHH kinds containing either cysteine or histidine residues. In the case of the CCCC core, the calculated energy barrier for the oxidation to sulfenate of the complexed thiolate was found to be 16.0 kcal mol À1 , which is 2 kcal mol À1 higher than that for the free thiolate. The energy barrier increases to 19.3 and 22.2 kcal mol À1 for the monoprotonated and diprotonated CCCC cores, respectively. Substitution of cysteine by histidine also induces an increase in the magnitude of the reaction energy barrier: It becomes 20.0 and 20.9 kcal mol À1 for the CCCH and CCHH cores, respectively. It is concluded that the energy barrier for the oxidation of zinc fingers is strictly dependent on the type of ligands coordinated to zinc and on the protonation state of the complex. These changes in the thiolate reactivity can be explained by the lowering of the nucleophilicity of complexed sulfur and by the internal reorganization of the complex (changes in the metalÀligand distances) upon oxidation. The next reaction steps subsequent to sulfenate formation are also considered. The oxidized thiolate (sulfenate) is predicted to dissociate very fast: For all complexes, the calculated dissociation energy barrier is lower than 3 kcal mol À1. It is also shown that the dissociated sulfenic acid can interact with a free thiolate to form a sulfurÀsulfur (SS) bridge in a reaction that is predicted to be quasi-diffusion limited. The interesting biological consequences of the modulation of thiolate reactivity by the chemical composition of the zinc finger cores are discussed.