All systems ↗Redox couples transfer electrons
NAD+/NADH, NADP+/NADPH, glutathione, thioredoxin, and other couples occupy different compartments and biochemical roles.
CELLULAR ENERGY / 07
Redox biology is control, not cleanup.
Electron-transfer reactions power metabolism and shape signaling. Reactive oxygen species can carry controlled information; when production, location, or defenses become mismatched, they can modify lipids, proteins, and nucleic acids.
Several sites produce ROS
Mitochondrial electron transport, NADPH oxidases, peroxisomes, ER reactions, and immune enzymes can generate reactive species.
Superoxide becomes peroxide
Superoxide dismutases convert superoxide toward hydrogen peroxide, a more stable species that can diffuse locally and modify sensitive proteins.
Location shapes meaning
A brief, localized peroxide signal differs from widespread persistent oxidation. Bulk measurements can miss the relevant compartment and timing.
Peroxidases reduce peroxides
Glutathione peroxidases and peroxiredoxins convert peroxides while passing oxidation into recyclable thiol systems.
Catalase handles hydrogen peroxide
Catalase is especially concentrated in peroxisomes and converts hydrogen peroxide to water and oxygen at high local loads.
NADPH restores capacity
Glutathione and thioredoxin reductases use NADPH to return oxidized defense systems toward their reduced state.
Repair and turnover finish the response
Damaged proteins, lipids, DNA, and organelles require repair, degradation, autophagy, or replacement—not only radical scavenging.