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Peroxiredoxins (Prxs) are a ubiquitous family of cysteine-dependent peroxidase enzymes that play dominant roles in regulating peroxide levels within cells. These enzymes, often present at high levels and capable of rapidly clearing peroxides, display a remarkable array of variations in their oligomeric states and susceptibility to regulation by hyperoxidative inactivation and other post-translational modifications. Key conserved residues within the active site promote catalysis by stabilizing the transition state required for transferring the terminal oxygen of hydroperoxides to the active site (peroxidatic) cysteine residue. Smartflash Tool P970h here. Extensive investigations continue to expand our understanding of the scope of their importance as well as the structures and forces at play within these critical defense and regulatory enzymes. Oxidative Stress Defenses and the Recently Recognized Importance of Peroxiredoxins Peroxiredoxins (Prxs) are ubiquitous enzymes that have emerged as arguably the most important and widespread peroxide and peroxynitrite scavenging enzymes in all of biology [, ]. Discovered to be widely-distributed peroxidases in the mid-1990’s [], the role of Prxs was long overshadowed by well-known oxidative stress defense enzymes such as catalase and glutathione peroxidase (Gpx).

However, refined kinetics measurements now imply that Prxs reduce more than 90% of cellular peroxides [, ]. Helping awaken interest in Prxs were several developments in the early 2000’s. It was shown that as little as ~100 μM hydrogen peroxide caused rapid inactivation of human Prx I by hyperoxidation during catalytic turnover [], and this sensitivity was shown to be due to conserved structural features within many eukaryotic Prxs [].

Vairamuthu Kavithaigal In Tamil Pdf Download here. The seemingly paradoxical finding that a peroxidase would be so easily inactivated by its own substrate led to the development of the ‘floodgate’ hypothesis [], which posits that Prx inactivation enables peroxide-mediated signaling in eukaryotes, a phenomenon now known to regulate many normal cellular functions []. Prx hyperoxidation was also shown to be reversible in vivo [] and the enzyme responsible for this “resurrection” was identified and named sulfiredoxin (Srx) []. Powerful addtional evidence that Prxs are crucial to proper cell regulation is that Prx I knockout mice develop severe hemolytic anemia as well as lymphomas, sarcomas and carcinomas by nine months of age []. Prxs have attracted the attention of cancer researchers not only for their apparent function as tumor suppressors (or in some circumstances promoters []), but also because they have elevated expression levels in various cancer tissues and immortalized cell lines. High Prx levels have been associated with the resistance of tumors and cancer-derived cell lines toward certain chemo- and radiotherapies [–].