Purine bases are substances that are formed in the human body mainly from low molecular weight precursors - products of the metabolism of carbohydrates and proteins. They play an important role in the construction of deoxyribonucleic and ribonucleic acids that carry genetic information. Various disorders of purine metabolism lead to severe health problems.
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 salts with mineral acids.
All purine bases are poorly soluble in water. With the addition of organic acids (benzoic, salicylic), their salts and an increase in temperature, the solubility of caffeine increases. The preparation of drugs with its content (diuretics, drugs for the treatment of migraine, infectious pathologies and poisonings accompanied by inhibition of the nervous system) is based on this property. Theophylline and theobromine are able to form salts with metals, which makes it possible to identify them.
Substance formation
Purine bases are synthesized in all cells of the human body, but mainly in the liver. 6 ATP molecules are spent on their formation.
External metabolism of these substances takes place in several stages:
Nucleoproteins enter the body with food.
Under the influence of enzymes of the class of hydrolases, they break down and release nucleic acids in the intestine.
Pancreatic juice hydrolyzes nucleic acids to polynucleotides.
In the intestine, they are further cleaved to mononucleotides.
Under the influence of enzymes, the latter turn into nucleosides containing nitrogenous bases associated with sugar.
Nucleosides are either absorbed in the intestinal lumen, or decompose to purine and pyrimidine bases.
Purine bases are substances that are regulated by the method of negative feedback. In other words, the final reaction product suppresses the initial stages of the process (using adenosine monophosphate and guanosine monophosphate). Key reactions of their synthesis are currently used to develop new antitumor agents.
Adenine and guanine
Adenine and guanine are purine bases, its amino derivatives. They are part of nucleotides, which are monomeric units of nucleic acids. The most important functions of purine bases in DNA are:
Adenine and guanine under laboratory conditions are obtained by hydrolysis of nucleic acids. Guanine is also isolated from fish scales and used in cosmetics as a pearlescent pigment.
Other functions in the body
In addition to nucleic acids, adenine and guanine are components of such important organic compounds as:
Adenosine, participating in biochemical processes (energy and nerve impulse transmission, anti-inflammatory effect). Scientists believe that this substance plays a role in regulating sleep.
Adenosine phosphates, which are necessary for the synthesis of ATP. 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 management, 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 effects on the body:
diuretic;
CNS stimulation, especially pronounced in caffeine;
increased heart rate;
an increase in the lumen of blood vessels (mainly those located in the muscles, brain, heart, and kidneys);
decrease in thrombosis.
Theobromine is also used to treat bronchopulmonary pathologies. Like caffeine, it stimulates the heart muscle and increases the amount of urine excreted. It is included in the composition of toothpastes to restore the mineralization of enamel and increase its hardness, resistance to caries. Theobromine is obtained from cocoa beans, ground, fat-free and boiled with a solution of sulfuric acid. After that, it is treated with lead oxide, washed and precipitated with ammonia.
Decay
The final substances in the metabolism of purine nucleic bases in the human body, 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 along with feces (up to 20%). Those compounds that are not oxidized in the intestinal lumen, but are absorbed, further decompose to uric acid.
According to scientists, nucleic acids that enter the body along with food are not sources of these substances, although their content in food reaches a significant amount.
The decomposition of purine bases in animals can occur before ammonia and urea. Some mammals also have an enzyme like uratoxidase. It converts uric acid to 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. Removal of uric acid through the intestine 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 in a healthy person per day is about 0.6 g.
Reuse
Reutilization of purine bases is a phenomenon consisting in their repeated use. This process is observed in tissues that grow rapidly (in embryos, during the regeneration of injuries, 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 in a shorter way, using the enzyme hypoxanthine guanine phosphoribosyl transferase. In the presence of genetic deficiency of this substance in children, a whole complex of pathological symptoms occurs, which are called Lesch-Nihan syndrome. Outwardly, this rare and almost incurable disease manifests itself in the form of mental retardation, impaired coordination of movements and extreme aggressiveness directed against himself.
Metabolic disorders
Violation of the 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 caused glycogen disease.
Xanthuria is a hereditary deficiency of the xanthine oxidase enzyme.
The formation of stones in the urinary system.
Gout and urolithiasis
With gout, uric acid synthesis far exceeds its amount excreted from the body. Since the solubility of the salts of this substance is small, they accumulate in the blood, soft tissues, 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 with the exception of foods rich in purine bases. Allopurinol, which inhibits the activity of converting the purine base of xanthine to uric acid, as well as agents to enhance its excretion (Anturan, Tsingofen and others), are used as medications.
Impaired metabolism of purine bases is one of the causes of urolithiasis. It is detected in half of people with gout. The increased content of urate 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 urate.
Nutrition
Natural and artificial sources of purine nucleic acid bases are:
caffeine - green tea leaves, coffee tree, cocoa, guarana (climbing vine of the genus Paullinia), soft drinks (cola and others);
theobromine - bean husk;
theophylline - green tea, coffee grains.
These compounds are also found in chocolate, meat, liver and red wine.