Purine bases are substances that are formed in the human body mainly from low molecular weight precursors - products of carbohydrate and protein metabolism. They play an important role in the construction of deoxyribonucleic and ribonucleic acids, which carry genetic information. Various disorders of purine metabolism lead to severe he alth disorders.
Description
Purine bases are derivatives of purine, organic natural compounds. The most famous and common of them are adenine, guanine, caffeine, theobromine, theophylline. The last three substances are very weak bases. Caffeine can be considered an almost neutral compound. Purines do not form s alts with mineral acids.
All purine bases are poorly soluble in water. With the addition of organic acids (benzoic, salicylic), their s alts and an increase in temperature, the solubility of caffeine increases. This property is based on obtainingdrugs with its content (diuretics, drugs for the treatment of migraine, infectious pathologies and poisonings, accompanied by depression of the nervous system). Theophylline and theobromine are able to form s alts with metals, which makes it possible to identify them.
Formation of substances
Synthesis of purine bases is produced in all cells of the human body, but mainly in the liver. It takes 6 ATP molecules to form them.
External metabolism of these substances takes place in several stages:
- Nucleoproteins enter the body with food.
- Under the influence of enzymes of the hydrolase class, they are cleaved and nucleic acids are released in the intestine.
- Pancreatic juice hydrolyses nucleic acids to polynucleotides.
- In the intestine, they are further broken down to mononucleotides.
- Under the influence of enzymes, the latter are converted into nucleosides containing nitrogenous bases associated with sugar.
- Nucleosides are either absorbed in the intestinal lumen or decomposed to purine and pyrimidine bases.
Purine bases are substances whose formation is regulated by a negative feedback method. In other words, the end product of the reaction suppresses the initial stages of the process (with the help of adenosine monophosphate and guanosine monophosphate). Keyreactions of their synthesis are currently used to develop new anticancer drugs.
Adenine and guanine
Adenine and guanine are purine bases, its amino derivatives. They are part of the nucleotides, which are the monomeric units of nucleic acids. The most important functions of purine bases in DNA are:
- storage and transmission of genetic information;
- participation in the process of cell division;
- protein biosynthesis;
- building cells.
Adenine and guanine in the laboratory are obtained by hydrolysis of nucleic acids. Guanine is also isolated from fish scales and used as a pearlescent pigment in cosmetics.
Other functions in the body
In addition to nucleic acids, adenine and guanine are constituents of such important organic compounds as:
-
Adenosine involved in biochemical processes (transmission of energy and nerve impulses, anti-inflammatory action). Scientists believe that this substance plays a role in regulating sleep.
- Adenosine phosphates, which are essential for ATP synthesis. The latter is an important source of energy in all biochemical processes in animals.
- Adenosine phosphoric acids (mono-, di- and triphosphoric) involved in protein biosynthesis, hormone regulation, lipid metabolism, steroid formation, regulation of cell membrane permeability.
- Adenine nucleotides responsible for lowering blood pressure, contractility of the uterus and heart muscle.
Purine bases are biologically active substances that have the following effect on the body:
- diuretic;
- stimulating the CNS, especially with caffeine;
- increased heart rate;
- enlargement of the lumen of blood vessels (mainly those in the muscles, brain, heart and kidneys);
- decrease in blood clots.
Theobromine is also used to treat bronchopulmonary pathologies. Like caffeine, it excites the heart muscle and increases the amount of urine produced. It is included in the composition of toothpastes to restore enamel mineralization and increase its hardness, resistance to caries. Theobromine is obtained from cocoa beans, ground, defatted and boiled with a solution of sulfuric acid. After that, it is treated with lead oxide, washed and precipitated with ammonia.
Decomposition
The final substances of the metabolism of purine nucleic bases in the body of humans, primates, birds and many mammals are hypoxanthine and uric acid, which is excreted mainly with urine, and only a small amount of it is released from the body with feces (up to 20%). Those compounds that are not oxidized in the intestinal lumen, but are absorbed, are also further decomposed to uric acid.
According to scientists, nucleic acids that enter the body with food are not sources of these substances, although their content in food reaches a significant amount.
Decomposition of purine bases in animals can occur to ammonia and urea. Some mammals also have an enzyme like urate oxidase. It converts uric acid into allantoin, which is more soluble in water. In metabolic disorders in humans, acid crystals are deposited in the muscles, fingers and cartilage, leading to the development of gout.
The decomposition of these compounds mainly occurs in the liver, small intestine and kidneys. The removal of uric acid through the intestines occurs along with bile, where, under the influence of microflora, this compound breaks down into carbon dioxide and water. The total amount of acid excreted per day in a he althy person is about 0.6 g.
Reuse
Recycling of purine bases is a phenomenon that consists in their repeated use. This process is observed in tissues that grow rapidly (in embryos, during the regeneration of damage, in tumors). In these cases, there is an active synthesis of nucleic acids, and the loss of their precursors (purine bases) becomes unacceptable.
The synthesis of nucleotides occurs along a shorter path, with the help of the enzyme hypoxanthine-guanine-phosphoribosyltransferase. In the presence of a genetic deficiency of this substance in children, a whole complex of pathological symptoms occurs,called the Lesch-Nyhan syndrome. Outwardly, this rare and practically incurable disease manifests itself in the form of mental retardation, impaired coordination of movements and extreme aggressiveness directed against oneself.
Violation of metabolic processes
Impaired metabolism of purine bases of nucleotide acids also leads to the following pathologies:
- Immunodeficiency caused by the absence of the enzyme nucleoside phosphorylase.
- Girke's disease is a genetically determined glycogen disease.
- Xanthinuria is a hereditary deficiency of the enzyme xanthine oxidase.
- Formation of stones in the urinary system.
Gout and urolithiasis
In gout, the synthesis of uric acid far exceeds the amount excreted from the body. Since the solubility of the s alts of this substance is low, they accumulate in the blood, soft tissues, and joints. This leads to the appearance of nodes and the development of inflammation (gouty arthritis). One of the symptoms of this disease is severe pain at night in the big toes.
In men, this pathology occurs 20 times more often than in women. The treatment for gout is a strict diet that avoids foods rich in purine bases. As medications, allopurinol is used, which inhibits the activity of converting the purine base of xanthine into uric acid, as well as agents to enhance its excretion.("Anturan", "Zinhofen" and others).
Violation of the exchange of purine bases is one of the causes of urolithiasis. It is found in half of people with gout. The increased content of urates in the urine leads to their deposition in the urinary tract. As a treatment, it is also recommended to follow a diet consisting mainly of plant foods. This promotes alkalization of urine and dissolution of urates.
Food
Natural and artificial sources of purine bases of nucleic acids are:
- caffeine - green tea leaves, coffee tree, cocoa, guarana (climbing liana of the genus Paulinia), soft drinks (cola and others);
- theobromine - bean husk;
- theophylline - green tea, coffee beans.
Also found in chocolate, meat, liver and red wine.
