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. 2006 Dec 4;175(5):779–789. doi: 10.1083/jcb.200606005

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Copyright © 2006, The Rockefeller University Press

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Figure 1. — The catalytic cycle of C-Cys eukaryotic Prxs. (A) When exposed to H₂O₂, the peroxidatic cysteine (S_PH) of 2-Cys Prxs is oxidized to sulfenic acid (Prx-SOH). Upon reaction with the resolving cysteine (S_RH), a Prx dimer with an intermolecular disulfide bond is formed, which is then reduced by Trx to regenerate active enzyme. Because of a pause in the catalytic cycle, the S_PH of eukaryotic 2-Cys Prxs is susceptible to hyperoxidation, resulting in the formation of a sulfinic acid form (Prx-SO₂H) that is catalytically inactive. Sulfiredoxins and sestrins are ATP-dependent sulfinyl reductases that participate in retroreduction of Prx-SO₂H, regenerating active enzyme. 2-Cys Prxs are obligate homodimers that can assemble into decamers and higher molecular mass oligomers, depending on oxidation state, pH, calcium concentrations, and posttranslational modifications such as phosphorylation.