Among all the substances on Earth, oxygen gas occupies a special place among them. It is its presence that makes our planet unique among all others, special. Thanks to this substance, so many beautiful creatures live in the world: plants, animals, people. Oxygen is an indispensable, unique and extremely important compound.
Oxygen is literally "the one that produces acid. The Russian word goes back to M.V. Lomonosov and is a tracing of the French word oxygène proposed by A.Lavoisier (from the Greek word ὀξύς - "acidic" and γεννάω - "born"). The atomic number of oxygen is 8; the atomic mass is 15,9994. The density of liquid oxygen is 1.144; the melting point is -218 ° C and the boiling point is -183 ° C. Oxygen is the third most abundant oxygen element in the Universe after hydrogen and helium. It is the most widespread chemical element on Earth - 47% of the mass of the Earth's crust, 85.7% of the mass of the hydrosphere, 23.15% of the mass of the atmosphere, 79% and 65% of the mass of plants and animals, respectively. The volume of oxygen is 92% of the Earth's crust.
- Functions of oxygen in living organisms - Participation in de novo biosynthesis of biologically active compounds;
- Participation in decontamination of biologically active or toxic metabolites;
- In reactions catalyzed by enzymes-oxygenases (exchange of Hairdryer and Tyre);
- 80-90% of the oxygen supply to cells is spent mainly on oxidation of substrates in tissue respiration;
- 2% of the Oxygen Fund is spent on the formation of NSAs.
Participation in de novo biosynthesis of biologically active compounds.
Attack and disruption of the peptide bond
The reaction sequence begins with the extraction of the hydrogen atom by the hydroxyl radical from any of the amino acid residues from the α-atom, resulting in the formation of the alkyl radical and water (a). Subsequent addition of the oxygen molecule to the alkyl radical results in the formation of an alkyl peroxyl radical (b), which then reacts with protonated superoxide anion (NO.2), or with Fe2+ and H+ (c). The formed alkyl peroxide can react with either (NF.2) or Fe2+ and H+, turning into an alkoxy radical. At this stage, it is possible either to break the peptide bond or to oxidize again by protonated superoxide or Fe2+ and H+ to the hydroxy derivative peptide (d). Alkyl-, peroxyl- and alkoxyl radicals of peptides can also abstract hydrogen atoms from amino acid residues, thus generating new radicals capable of entering into similar radicals. In the absence or lack of O2, two alkyl derivatives of peptides can interact with each other to form intra- and/or inter-peptide cross-links.
There are 4 mechanisms of peptide bonding breaking caused by active oxygen forms:
- Splitting of alkoxyl derivatives of peptides through the α-amide pathway
- A diamide nitrogen cyanide derivative is formed from the N-terminus of the peptide
- Splitting alkoxyl derivatives of peptides through the diamide pathway
- Diamide and α-ketoacid derivative are formed from the former N-terminus
- 3) Oxidation of side parts of glutamylic and aspartic residues
- Example: Oxidation of glutamate
- The decomposition begins with the extraction of the hydrogen atom by the hydroxyl radical from the γ-atom of the carbon glutamine residue. This is followed by a series of transformations similar to the above, and oxalic acid is formed and the peptide bond is broken down. The fragment formed from the N-terminal part of the initial polypeptide is represented by amide, and from the C-terminal part - by pyruvial part.
- 4) Proline residue oxidation
- If polypeptide contains residues of monoamine dicarboxylic acids, they can also be oxidized by specific decomposition of peptide bonds.
G. Schüssler and K. Schilling found that the number of peptides produced is comparable to the number of proline residues. And the oxidation of proline residues leads to the formation of 2-pyrrolidine derivatives and the splitting of the peptide bond. As a result of acid hydrolysis, 2-pyrrolidone turns into 4-amino-butyric acid, its presence is regarded as proof of the splitting of peptides along 2 pyrrolidone pathways.
Iron ions play a huge role in the free radical oxidation of proteins. They are electron donors and thus initiate this process. In several pathological cases, iron ions can be released from cellular depots, which leads to the intensification of free-radical processes with the resulting consequences.