The types of oxidation


The concept about oxidase’s type

80% of O2 is used for this type. It is also named biologic oxidation. It is a 1-st type of oxidation that is 1 molecule of O2 is reduced by 4 electrons. This type serves as source of energy which need for synthesis of ATP

Oxygenase’s type of oxidation

20% of O2 is used for other types of oxidation. This type occurs in 2 pathways – mono- and dioxygenetic. In the monooxygenase’s pathway the substrate is oxidized by 1 atom of oxygen, other atom is used for the formation of water. This pathway occurs in mitochondrions and microsomes. The formation of metabolic-active forms of vitamin D, cholesterol, bile acids and corticosteroids occurs in mitochondrions. The oxidation in microsomes is named microsomic. It can occur as hydroxylation (in participation of NADPH2). In this case the oxidated product containing OH group, water and NADP are formed. Microsomic oxidation occurs in microsomes of liver. In this kind of oxidation the multienzymatic membrane’s system including NADPH2, FP and CytP450 participate. This type of oxidation is a preventive reaction of the body because the oxidation of different xenobiotics occurs. In dioxygenase’s pathwway the including of whole molecule of O2 in substrate occurs. Usually it occurs with substances having unsaturated bonds, for example, PUFA. The including of O2 occurs in site of rupture of double bond: S + O2 --> SO2.

Peroxide’s type of oxidation or free radical or lipid peroxidation (LPO)

It occurs in 1 electron reduction of O2. PUFA undergo to this type too. LPO is iniciated under action of active forms of O2 (AFO) such as superoxideanion, peroxide radical, hydroxy radical, radical of NO, hypochlorite anion etc. AFO are formed in the interaction of O2 with metals of variable valency: O2 + Fe++ à ·O2 + Fe+++

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

VITAMINS

When we read books or see movies about great geografical discoveries we imagine Columbus and his team, Vasko de Gamma and other travelers as handsome healthy people because they are heroes. But it is not true. Those heroes reached new lands, the North and the South Poles, but they were sick men without teeth, with bleeding mouth, with infringement of sight, suffering from polyneuritis. They reached purposes, new discoveries cost lives because there were no vitamins in their food, as they were discovered only at the beginning of twentieth of our century.

Vitamin is low molecular organic nutrients, which is necessary for normal healthy life of men, animals and microorganismus; for fulfillment of special cellular functions. Its name a derivation from two Latin words: vita – life, and amin, so it means amin, which is necessary for life.

Their presence is necessary for normal life. Vitamins are important nutrients for life’s work, though do not fulfill any energetic or structural functions. Many of them are a part of enzymes and thus they take part in regulation of metabolism.

Nowadays is proved that many of vitamins have a few molecular forms, named vitameres. For the vitD seven vitameres are known, for the vitK – three vitameres and et cetera. All vitameres have same biological action.

Fresh food and the intestinal microflora are the sources of vitamins for the men, but the intestinal microflora is not able to synthesize the necessary quantity of vitamins. That is why entering of vitamins and provitamins (prov) are compulsory. Prov is inactive form of vitamin, which transforms in active in different body’s organs – often in a liver, sometimes in the kidneys. In the case of violation of v. Entering disbalance is developed. When the quantity of v. Is not sufficient it is negative the so called v. Deficiency – avitaminose and hypovitaminose. Nowadays practically we meet only the last (hypo-). Positive misbalance is developed in the case of abundant v-s. It is called hypervitaminose. The external reasons for the negative misbalance may be the following:

1. the absence in food or not sufficient quantity of v-s, prov-s, or fat and other nutrients which are necessary for suction;

2. presence of antivitamins in food.

The inner reasons may be the following:

1. gastro-intestinal diseases, which are leading to the violation of suction.

2. Intestinal worms, by the reasons of compete suction, because the worms need in v-s also as a man.

3. The violation of endogenous (interior) synthesis

Antivitamins are the nutrients that cause the reduction or the loss of the biological activity of v-s and act as competitors. They may have the structure similar with the v-s. Entering in the enzymes as coenzymes they create an inactive enzyme complex.

That is why av-s may be used as antibacterial means. They stop life and division of microorganisms. There are av-s that cause the reduction or the loss of biological activity of v-s by changing their chemical nature.

Nowadays there are about thirty v-s. So we need their nomenclature and classification.

In 1956 biochemical section of International council on pure and applied chemistry had established chemical designations for v-s. Nowadays we have three kinds of the v-s. Names reflecting the chemical structure and the biological significance used.

V-s are divided into three large groups:

1. V-s that are dissolved in water;

2. V-s that are dissolved in fat;

3. Substances like v-s

1. first group – v-s dissolving in water. The peculiarity of this group is that most of them take part in building of cof-s of different ferments. This group is divided into two subgroupes, nfirst of them is v-s of the group B.

To this group we refer v-s dissolved in water and containing nitrogen in their molecules.

Spreading in nature. V-s of these group are contained in the coats and buds of cereals. There are plenty of them in flour, in bran, in yeast. The vBc is found in green parts of plants. They are contained, but less in such products as a liver, kidneys, brain, the egg yolk. The vB12 is met only in food of the animal origin: in a liver, kidneys, lungs, in a spleen.

The day’s need for a healthy grown-up is about 2-3 mg for each of v-s, except niacyn, the need in it is about 25mg, B12 – 0,025mg. Children, sick people and pregnant women need more v-s.



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