Category: signaling
Reactive oxygen + nitrogen species (superoxide O2•−, hydrogen peroxide H2O2, hydroxyl •OH, peroxynitrite ONOO−). Sources: (1) mitochondrial ETC leak at Complex I + III; (2) NADPH oxidase (NOX family — NOX2 in neutrophils for respiratory burst; NOX4 widely expressed); (3) xanthine oxidase; (4) NOS uncoupling (eNOS without BH4 makes O2•− instead of NO). Defenses: superoxide dismutase (SOD1 cytosol, SOD2 mitochondria) → H2O2 → catalase + glutathione peroxidase (selenium) + peroxiredoxins (thioredoxin-dependent). Glutathione + NADPH + vitamin C + vitamin E + bilirubin = small-molecule antioxidants. Pathologic ROS underlies ischemia-reperfusion injury, neurodegeneration, atherosclerosis. NRF2-KEAP1 axis induces antioxidant gene transcription (sulforaphane activator; dimethyl fumarate for MS).