Oxygen Toxicity and Free Radical Injury

Catalyses 2O₂^- + 2H⁺ -> H₂O₂ + O₂ - first line of defense against free radicals

H₂O₂ converts to OH^- and ·OH in the presence of Fe²⁺

Hydrogen Peroxide and superoxide react to form O₂ water and peroxyl radical. Catalysed by Fe²⁺

Part of the electron transport chain in the mitochondria, it is a source of ROS when it sometimes loses it electron to a molecule of dioxygen -> superoxide

3C, =O on either end. Forms when lipids are attacked by free radicals. Water soluble and a blood marker for free radical damage.

Class of enzymes found in the liver which metabolise certain organic compounds, e.g. drugs, alcohol. May release free radicals, particularly when metabolising certain substances for which there is not an onward pathway, => intermediate products are released. Example is metabolism of CCl₄ (used in dry-cleaning industry). First step oxidises it, producing CCl₃· and Cl. There is no onward pathway, so the reaction products are released and may cause damage.
In the presence of suitable substrates, these enzymes are induced (upregulated)

Lose active transportMembrane proteins may become cross-linked
Influx of Ca²⁺, Na⁺ -> Influx of H₂O -> cell swelling / lysis

Lysine, Histidine, proline, arginine, methionine. Cysteine and methionine are sulphur-containing

Neurodegenerative disorders, e.g. PDDown's SyndromeRheumatoid arthritisReperfusion injuryDMDAlcohol-induced liver diseaseMS

Catalyses first reaction of the respiratory burst (dioxide --> Superoxide) by oxidising NADPH. Enzyme is membrane bound in phagocytic cells

Secreted into phagolysosomes during respiratory burst. Heme containing - gives pus a green colour. Catalyses H₂O₂ -> HOCl

Catalyses the production of NO to be released into phagolysosome during respiratory burst. NO may go on to combine with superoxide to produce ONOO^- (peroxynitrate) which may then produce RNOS.

Catalyses 2H₂O₂ -> 2H₂O + O₂

Found in green tea, red wine, chocolate, etc. Antioxidant protection is unclear - chelate Fe + Cu, Inhibit superoxide producing enzymes, free radical scavengers?

- alpha tocopherol - lipid soluble, stays in membrane - donates electron to radical, e.g. LOO· ->forms tocopheryl radical - radical form tends to DONATE SECOND ELECTRON, thereby stopping another radical chain, rather than seeking to oxidise something else.