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Superoxide anion

2H⁺ + ·O2 + ·O2 -----à H2O2 + O2 (SOD)

H2O2 à 2H2O + O2 (catalase)

H2O2 + ·O2 --à ·OH + ^–OH + O2 (Haber-Weis reaction)

H2O2 + HCl à H2O + HOCl (myeloperoxidase)

2GSH + ROOH à GSSG + H2O +ROH (GPO)

GSSG à 2GSH (with NADPH2 and GR)

Hydrogen peroxide (H2O2) interacting with ·O2 can form ·OH. AFO are dangerous for cells in a large amount. ·O2 can cause the depolymerization of GAG, oxidation of epinephrine and thiols. Hydrogen peroxide is toxic too. Its excess causes the oxidation of thiogroups of proteins and can lead to formation of ·OH. The main danger of AFO is their ability to initiate LPO.

LPO has a chain character. In normal conditions LPO occurs in a small scale and is necessary for: 1) formation of prostanoids; 2) utilization of PUFA. Proteins and nucleic acids undergo to LPO too. It causes a derangement of their functions. A high velocity of LPO is able to cause the damage of membrane and death of cells. But in small scale LPO is necessary for renew of cells membranes. The velocity of LPO is controlled by antioxidant system (AOS). It is divided into enzymatic and nonenzymatic. To enzymatic AOS are referred: 1) SOD which translates ·O2 to H2O2: 2·O2 + 2H⁺ à H2O2 + O2; 2) catalase which breaks H2O2 to water and O2; 3) glutathione peroxidase (GPO) which reduces the hydroperoxides of lipids to oxiacids. in the result of reaction the oxidated glutathione (GSSG) and water are formed; 4) glutathione reductase (GR) reducing the oxidated glutathione. The cells of animals usually contain a large quantity of reduced and less quantity of oxidated glutathione. There are also present mix disulfides of reduced glutathione with proteins in the cells.

Fat soluble vitamins, vitamin C, P, B2, carnosine (which neutralizes ·OH), ferritin (binds Fe⁺⁺ ), ceruloplasmin (binds Cu⁺⁺ ), metalothineins (bind some metals), taurine (neutralizes OHCl) are referred to nonenzymatic AOS.

Peroxidase’s type

It occurs with participation of some substances possesing by autooxidability. Some flavoproteins (xanthine oxidase, MAO, DAO etc) are referred to these substances.

SH2 + FP à FPH2 + S (oxidated);

FPH2 + O2 à FP + H2O2.

This type is a collateral pathway of oxidation. It is usually observed in damage of cytochrome system or in the case when the substrate isn’t oxidized by other way, for example uric acid

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