Figure 1From: Peroxiredoxins: hidden players in the antioxidant defence of human spermatozoaRe-activation of PRDXs. (1) PRDXs scavenge H2O2 and become oxidized and inactive (2). This inactivation is reversed by the thioredoxin (TRX)-TRX reductase (TRD) system that uses NADPH as reducing equivalents (3). (4) Further thiol oxidation of PRDXs by higher levels of H2O2 (hyperoxidation) radically inactivates the enzyme allowing H2O2 levels to increase in the cell and to trigger the H2O2-dependent signaling. This inactivation must be transient to avoid toxic effects by high levels of H2O2; thus, after transmission of the signal, SRX/sestrins re-activate PRDXs using ATP (P = phosphate group) (5). (6) Finally, donors of SH groups such as GSH or TRX, reduce PRDX.Back to article page