Illustration of the mechanism of redox regulation by perox-iredoxin 6 (Prdx6). Prdx6 detoxifies and controls intracellular levels of reactive oxidative species (ROS), providing cytoprotection by maintaining survival signaling. The active site cysteine (Cys47) is oxidized to cysteine sulfenic acid (Cys47-SOH) by hydrogen peroxide (H2O2). However, the resulting Cys47-SOH cannot form a disulfide bond because no other Cys-SH residues are present nearby. Cys47-SOH can be reduced by nonphysiologic thiols. Occasionally, the sulfenic intermediate is hyperoxidized to sulfinic (Cys-SO2H) or sulfonic (Cys-SO3H) acid, inactivating its peroxidase activity. GST Glutathione-S-transferase, UV-B ultraviolet B