Figure 1.

Schematic representation of the relationships among free oxygen radical formation, enzymatic antioxidant systems, and lipid peroxidation. O₂⁻, superoxide anion radical; O₂, molecular oxygen; H⁺, hydrogen ion, proton; H₂O, water; SOD, superoxide dismutase; CAT, catalase; H₂O₂, hydrogen peroxide; GSH-Px, glutathione reductase; GSH, reduced glutathione; GSSG, oxidized glutathione; GSH-Red, glutathione reductase; NADPH + H⁺, reduced nicotinamide adenine dinucleotide phosphate; NADP⁺, oxidized nicotinamide adenine dinucleotide phosphate; Fe⁺⁺, ferrous iron; OH⁻, hydroxyl ion; .OH, hydroxyl radical (the most potent free radical); tNOS, total nitric oxide synthases (neuronal NOS, endothelial NOS, and inducible NOS); NO., nitric oxide radical; ONOO⁻, peroxynitrite; MDA, malondialdehyde (the last product of lipid peroxidation of membrane phospholipids); NO₂, nitrite; PUFA, polyunsaturated fatty acid; XO, xanthine oxidase.