Xanthine arises as an intermediate product in the breakdown of purine nucleotides to uric acid. It thus represents a central molecule in the context of nucleic acid metabolism. If the breakdown of xanthine is disturbed, so-called xanthineuria occurs.
What is xanthine?
Xanthine is an intermediate product in the breakdown of purines in the organism. The most important starting compounds are the purine bases adenine and guanine, which are derived from nucleic acid metabolism. It is also the lead substance in the xanthine group.
Xanthine consists of a hetero ring with six atoms, to which another hetero ring with five atoms is connected. The basic structure of the xanthines contains a nitrogen atom at positions 1, 3, 7 and 9. Positions 4 and 5 each contain carbon atoms that belong to both rings. The remaining of the total of 9 positions consist of carbon atoms to which different atoms or groups of atoms are bound depending on the compound. In the case of xanthine, positions 2 and 6 are hydroxylated.
However, when the aroma structure is broken up, the hydrogen ion of the hydroxyl group migrates to the ring nitrogen. In the process, C = O double bonds and NH single bonds are formed. Xanthine is a colorless and crystalline solid with a melting point of 360 degrees. It is only sparingly soluble in cold water and moderately soluble in hot water. It also dissolves in alcohol. The xanthines also include the active ingredients caffeine, theobromine and theophylline.
Function, effect & tasks
As mentioned earlier, xanthine is an intermediate product in the breakdown of purines in the body. The reverse reaction from xanthine to the purine bases is not possible. Once it has arisen, it is excreted by the body, converting it into uric acid.
This process removes a large part of the nitrogen in the body. The purine bases as components of the nucleic acids are synthesized from amino acids. No free purine bases are produced during the synthesis, only their nucleotides. Ribose phosphate serves as the starting molecule, on which the basic structure of the purine base is synthesized by adding atoms and groups of atoms. These atom groups come from the amino acid metabolism. Since this process is very energy-intensive, purine bases are recovered from nucleic acids via the so-called salvage pathway and re-incorporated into the nucleic acids as a mononucleotide.
The new synthesis of the purine bases and their breakdown are balanced. The better the salvage pathway, i.e. the recycling of purine bases, works, the less xanthine and thus also uric acid the body produces. When this process is disturbed, the metabolic rate for the formation of xanthine increases. The formation of xanthine is catalyzed by the enzyme xanthine oxidase. With the help of xanthine oxidase, the intermediate products of purine breakdown, hypoxanthine and xanthine, are formed. In addition to its important function as an intermediate in the breakdown of purines, its chemical structure in the body also has a stimulating effect.
Education, occurrence, properties & optimal values
Xanthine is found in the blood, muscles, and liver. It is produced during the hydroxylation of the purine bases at positions 2 and 6. It is also the lead substance of various alkaloids such as caffeine, theobromine or theophylline. These substances are found in coffee beans, cocoa, tea leaves, mate, guarana or cola nuts and are known for their stimulating effect.
The same goes for xanthine. A stimulating effect is ascribed to the xanthine. In wine it is formed to a small extent when yeasts break down. In addition to the other xanthine derivatives, xanthine is also found in coffee beans, tea, mate and even in potatoes. The particularly stimulating effect of the mate tea is said to be due to the influence of xanthine. Like the other purine bases, it forms nucleosides and nucleotides. The nucleoside xanthosine consists of the sugar ribofuranose and xanthine.
A well-known nucleotide is xanthosine monophosphate (XMP), which is formed from xanthine, ribose and phosphate. Guanisimonophosphate (GMP) is formed from XMP in the body as a basic building block of the RNA. Like GMP, XMP is also used as a flavor enhancer. Xanthine can form base pairs with other purine bases via hydrogen bonds. With the help of 2,4-diaminopyrimidine and xanthine, unusual base pairings are investigated to better understand the processes in DNA.
Diseases & Disorders
A disease in connection with xanthine is the so-called xanthineuria. Xanthineuria is a genetic metabolic disorder in the purine metabolism. Due to a mutation, the enzyme xanthine oxidase (XO) is not or only partially functional.
Xanthine oxidase is responsible for catalyzing the breakdown of hypoxanthine and xanthine into uric acid. When the breakdown stops working, xanthine collects in the blood. Hypoxanthine can be recycled via the salvage pathway and returned to the purine metabolism. However, this is no longer possible for xanthine. Since it is soluble in water, it can be excreted in the urine. The uric acid levels are low. In rare cases this can lead to xanthine deposits in the muscles or other organs. In extreme cases, xanthine stones in the kidneys lead to acute kidney failure.
Type II xanthinuria is associated with autism, mental retardation, kidney cysts, nephrocalcinosis, and decreased bone density, among other things. A lot of drinking and a low-purine diet are recommended as therapy. Xanthinuria can also develop from drug treatment of gout with allopurinol. Allopurinol works by blocking the enzyme xanthine oxidase to lower uric acid levels. Instead of increased uric acid production, the xanthine concentration increases. To prevent kidney stone formation, the fluid intake must be increased.
