Importance Of Srx In Cell Signalling And Defense

Intracellular levels of peroxide are tightly regulated and kept at nM levels (Seaver et al., 2001). In contrast to bacteria where peroxide generally is viewed as toxic and rapidly eliminated, higher organisms utilize intermediate levels of peroxide in cell signaling (Rhee, 2006). In an effort to designate a cellular role for the hyperoxidation of typical 2-Cys peroxiredoxin in cell signaling, the floodgate hypothesis was proposed (Wood et al., 2003). In this proposal the Prx molecule and its...

Relevance Of Peroxiredoxincatalyzed Peroxynitrite Detoxification

Peroxynitrite's relevance in biochemistry was first noted by Beckman et al. (1990) and Radi et al. (1991) and during the next ten years evidence of the formation of this oxidant in vivo accumulated. Initially considered a toxic species, peroxynitrite, like H2O2 (Rhee, 2006), has recently started to be regarded as potentially involved in redox signaling pathways (Bachschmid, et al., 2005 Touyz, 2005). By 2000, the mechanisms that control peroxynitrite toxicity and possible signaling functions...

Structure Of Sulfiredoxin And Putative Interactions With Prxs

In an effort to understand the molecular basis for the novel sulfur chemistry mediated by Srx and the Srx Prx interaction, the structure of human Srx has been determined by X-ray crystallography and NMR (PDB codes lXW3, lXW4, and lYZS) (Jonsson et al., 2005 Lee et al., 2005). These structures have revealed a unique protein fold and nucleotide-binding motif. These studies have also laid the foundation for future structural work and the biochemical characterization of site-directed mutants to...

Discovery Of The Peroxidase Activity Of Peroxiredoxins

As is evident from the above, a common enzymatic nature of the peroxiredoxins did not emerge for quite a while and has not yet been established for all members of the family. As a rule, however, peroxiredoxins are now considered to be peroxidases. The first essentially correct assignment of an enzymatic activity to a peroxire-doxin system was that of an alkyl hydroperoxide reductase to the ahp gene product of enterobacteria. Searching for new tester strains that specifically responded to...

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Competition kinetics for determining the rate constant of hydrogen peroxide-dependent Tb cTXNPx oxidation.A) Horseradish peroxidase (2 M) was exposed to H2O2 (0.25 M) in sodium phosphate buffer pH 7.4 and 25 C, either in the absence or in the presence of the indicated concentrations of reduced TbcTXNPx. Changes in absorbance at 397.5 nm, reflecting Compound I formation were determined. B) The absorbance changes shown were fitted to exponential decays, and amplitudes of the exponential...

The Hyperoxidation Of Peroxiredoxins

Early studies on oxidative stress in yeast revealed that a 25kDa protein called thiol specific antioxidant protein (TSA) was able to protect glutamate synthetase from inactivation in the presence of Fe3+, O2 and dithiothreitol (DTT) (Kim et al 1985). TSA was later shown to belong to the ubiquitous peroxiredoxin family (Chae et al., 1994) that uses redox-sensitive cysteine residues to detoxify hydrogen peroxide, lipid hydroperoxides and peroxynitrite. As a result of kinetic studies that showed...

Retroreduction Of Typical 2cys Peroxiredoxins

Protein cysteine sulfinic acid formation is not unusual given that 1-2 of the cysteine residues of soluble proteins from rat liver were detected in this oxidation state (Hamann et al., 2002). Until recently these cysteine derivatives were viewed as irreversible although sulfinic acids can be reduced in vitro by reductants such as 2-mercaptoethanol under very acidic (< pH4) conditions (Finlayson, 1979 Claiborne et al., 1999). Interestingly, bacteria have enzymatic systems, such as the E. coli...

Peroxiredoxins In Prokaryotes

Historically, before the eukaryotic peroxiredoxin TSA from Saccharomyces cerevisiae was characterized (Kim et al., 1988), another antioxidant enzyme from the prokaryotes Salmonella typhimurium and Escherichia coli had been identified as a peroxidase of the alkyl hydroperoxide reductase system and was named AhpC for alkyl hydroperoxide reductase subunit C (Jacobson et al., 1989). This alkyl hydroperoxide reductase system was shown to be composed of the 21-kDa AhpC and the 57-kDa flavoprotein...

Catalytic Properties Of

Since the initial characterization of yeast Srx1 and the determination of the human Srx structure, several studies have provided further insight into the catalytic mechanism and substrate specificity of human and rat Srx. In these studies three activity assays have been utilized (i) sulfinic acid reductase activity based on the decrease in the immuno-reactive band to Prx-SO2 3-, (ii) ATPase activity corresponding to the increase in the amount of inorganic phosphate released, (iii) binding of...

Peroxidelinked Redox Signalling

Modification of proteins by redox processes has for long been discussed as a concept of regulating cellular events. Starting in 1965 Pontremoli and Horrecker Nakashima et al., 1969 Pontremoli et al., 1965 Pontremoli et al., 1967 reported on the activation of fructose diphosphatase and, in consequence, gluconeogenesis by physiological disulfides such as cystamine and oxidized CoA, and later hydroperoxide exposure was shown to induce gluconeogenesis in perfused rat liver Sies et al., 1972 ....

References

Apel, K., and Hirt, H., 2004, Reactive oxygen species metabolism, oxidative stress, and signal transduction. Annu. Rev. Plant Biol. 55 373-399. Baker, L. M., Raudonikiene, A., Hoffman, P. S., and Poole, L. B., 2001, Essential thioredoxin-dependent peroxiredoxin system from Helicobacter pylori genetic and kinetic characterization. J. Bacteriol. 183 1961-1973. Basu, M. K., and Koonin, E. V., 2005, Evolution of eukaryotic cysteine sulfinic acid reductase, sulfire- doxin Srx , from bacterial...

General Approaches To Study Peroxiredoxin Kinetics

The kinetics of the reactions catalyzed by Prxs has been studied by two complementary approaches, i.e. steady-state analysis in the presence of both the reducing and the oxidizing substrate and low, catalytic concentrations of the enzyme, or pre-steady state analysis of particular steps in the catalytic cycle. The two approaches yielded convergent results that also complied with independent analyses of catalytic intermediates, with investigations of molecular mutants and, in many cases, with...