Fig. 7

Model of H₂O₂ scavenging and sensing at different oxidant concentrations. From our experimental data and applied biochemical equations, we propose three scenarios depending on the extracellular peroxide levels. A permeability gradient of 40:1 (extracellular to intracellular) is indicated, with further gradients achieved only when Tpx1 is fully active. At 2–50 μM extracellular peroxides, Tpx1 acts as the only H₂O₂ scavenger, while at sub-toxic doses of extracellular peroxide (100–200 μM), both Tpx1 and Ctt1 act as scavengers. Finally, at toxic levels of extracellular peroxides (300–1000 μM), the main intracellular scavenger of peroxides is Ctt1. Regarding signaling, while OxyR senses peroxides at both sub-toxic (100–200 μM) and toxic (0.3–1 mM) doses, Pap1 is active only at the intermediate concentrations, due to Tpx1 acting as a scavenger at the lowest doses thanks to Trx1-mediated recycling, and Tpx1 being over-oxidized to the sulfinic acid form at the highest H₂O₂ doses