Properties of Reactive Oxygen Species
| Superoxide: | Mild oxidant and reductant with limited biological activity; reduces some iron complexes to enable hydroxyl radical production by the Fenton reaction; inactivates iron/sulfur proteins and releases iron; limited membrane permeability. |
| Hydrogen peroxide: | Oxidizing agent; reacts slowly with reducing agents such as thiols; reacts with reduced iron and copper salts to generate hydroxyl radicals; reacts with heme proteins and peroxidases to initiate radical reactions and lipid peroxidation; membrane permeable. |
| Hydroxyl radical: | Extremely reactive with most biological molecules; causes DNA modification and strand breaks, enzyme inactivation, lipid peroxidation; very short range of action; generates secondary radicals, eg, from bicarbonate, chloride. |
| Singlet oxygen: | Electronically excited state of oxygen; reacts with a number of biological molecules, including membrane lipids to initiate peroxidation. |
| Hypochlorous acid: | Strong nonradical oxidant of a wide range of biological compounds, but more selective than hydroxyl radical; preferred substrates thiols and thioethers; converts amines to chloramines; chlorinates phenols and unsaturated bonds; oxidizes iron centers; crosslinks proteins; membrane permeable; in equilibrium with chlorine gas at low pH and hypochlorite at high pH. |
| Chloramines: | Milder and longer lived oxidants than HOCl; react with thiols, thioethers, iron centers; variable toxicity dependent on polarity and membrane permeability; chloramines of α-amino acids break down slowly to potentially toxic aldehydes. |
| Nitric oxide: | Reacts very rapidly with superoxide to give peroxynitrite; reaction with oxygen favored at high oxygen tension; forms complexes with heme proteins; inactivates iron/sulfur centers; forms nitrosothiols. |
| Peroxynitrite: | Unstable short lived strong oxidant with properties similar to hydroxyl radical; hydroxylates and nitrates aromatic compounds; reacts rapidly with thiols: breaks down to nitrate; interacts with bicarbonate to alter reactivity. |
| Superoxide: | Mild oxidant and reductant with limited biological activity; reduces some iron complexes to enable hydroxyl radical production by the Fenton reaction; inactivates iron/sulfur proteins and releases iron; limited membrane permeability. |
| Hydrogen peroxide: | Oxidizing agent; reacts slowly with reducing agents such as thiols; reacts with reduced iron and copper salts to generate hydroxyl radicals; reacts with heme proteins and peroxidases to initiate radical reactions and lipid peroxidation; membrane permeable. |
| Hydroxyl radical: | Extremely reactive with most biological molecules; causes DNA modification and strand breaks, enzyme inactivation, lipid peroxidation; very short range of action; generates secondary radicals, eg, from bicarbonate, chloride. |
| Singlet oxygen: | Electronically excited state of oxygen; reacts with a number of biological molecules, including membrane lipids to initiate peroxidation. |
| Hypochlorous acid: | Strong nonradical oxidant of a wide range of biological compounds, but more selective than hydroxyl radical; preferred substrates thiols and thioethers; converts amines to chloramines; chlorinates phenols and unsaturated bonds; oxidizes iron centers; crosslinks proteins; membrane permeable; in equilibrium with chlorine gas at low pH and hypochlorite at high pH. |
| Chloramines: | Milder and longer lived oxidants than HOCl; react with thiols, thioethers, iron centers; variable toxicity dependent on polarity and membrane permeability; chloramines of α-amino acids break down slowly to potentially toxic aldehydes. |
| Nitric oxide: | Reacts very rapidly with superoxide to give peroxynitrite; reaction with oxygen favored at high oxygen tension; forms complexes with heme proteins; inactivates iron/sulfur centers; forms nitrosothiols. |
| Peroxynitrite: | Unstable short lived strong oxidant with properties similar to hydroxyl radical; hydroxylates and nitrates aromatic compounds; reacts rapidly with thiols: breaks down to nitrate; interacts with bicarbonate to alter reactivity. |