Xanthine is formed as an intermediate in the breakdown of purine nucleotides to uric acid. Thus, it represents a central molecule in the context of nucleic acid metabolism. When xanthine degradation is disturbed, so-called xanthinuria occurs.
What is xanthine?
Xanthine represents an intermediate product in purine degradation in the organism. The most important starting compounds are the purine bases adenine and guanine, which originate from nucleic acid metabolism. It is also the lead substance in the group of xanthines. Xanthine consists of a hetero ring with six atoms, to which another hetero ring with five atoms is attached. The basic skeleton of xanthines contains a nitrogen atom at positions 1, 3, 7 and 9, respectively. Positions 4 and 5 each contain carbon atoms, which belong to both rings. The remaining 9 positions consist of carbon atoms to which different atoms or groups of atoms are attached, depending on the compound. In the case of xanthine, positions 2 and 6 are hydroxylated in each case. 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 shows up as a colorless and crystalline solid with a melting point of 360 degrees. It is only slightly soluble in cold water and moderately soluble in hot water. Furthermore, it dissolves in alcohol. Xanthines also include the active ingredients caffeine, theobromine, or theophylline, among others.
Function, effect and tasks
As mentioned earlier, xanthine is an intermediate in the breakdown of purines in the body. The reverse reaction of xanthine to purine bases is not possible. Once it is formed, it is excreted from the body under conversion to uric acid. Through this process, much of the nitrogen in the body is disposed of. Purine bases, as components of nucleic acids, are synthesized from amino acids. During synthesis, no free purine bases are formed, only their nucleotides. Ribose phosphate serves as the starting molecule, to which the basic structure of the purine base is synthesized by attaching atoms and atom groups. These atom groups originate from amino acid metabolism. Since this process is very energy-intensive, purine bases are recovered from nucleic acids via the so-called salvage pathway and reincorporated into the nucleic acids as mononucleotides. The new synthesis of purine bases and their degradation balance each other out. The better the salvage pathway, i.e. the recycling of the purine bases, functions, the less xanthine and thus uric acid the body produces. When this process is disturbed, the metabolic rate to form xanthine increases. The formation of xanthine is catalyzed by the enzyme xanthine oxidase. With the help of xanthine oxidase, the intermediates of purine degradation, hypoxanthine and xanthine, are formed. In addition to its important function as an intermediate in the breakdown of purines, it also has a stimulating effect due to its chemical structure in the body.
Formation, occurrence, properties, and optimal values
Xanthine is found in the blood, muscles and liver. It is formed during the hydroxylation of purine bases at positions 2 and 6. It also represents 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 kola nuts and are known for their stimulating effect. The same is true for xanthine. Thus, xanthine is also said to have a stimulating effect. In wine, it is formed to a small extent during the decomposition of yeasts. In addition to the other xanthine derivatives, xanthine is also found in coffee beans, tea, mate and even potatoes. The particular stimulating effect of mate tea is said to be due to the influence of xanthine. Like the other purine bases, it forms nucleosides and nucleotides. Thus, 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. XMP forms guanisimonophosphate (GMP) in the body as a basic building block of 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 being studied to better understand processes in DNA.
Diseases and disorders
One disorder associated with xanthine is known as xanthinuria.Xanthinuria is a genetically caused metabolic disorder in purine metabolism. Due to a mutation, the enzyme xanthine oxidase (XO) is not functional or only partially functional. Xanthine oxidase is responsible for catalyzing the breakdown of hypoxanthine and xanthine into uric acid. When the degradation stops functioning, xanthine accumulates in the blood. Hypoxanthine can be recycled via the salvage pathway and returned to purine metabolism. However, this is no longer possible for xanthine. Since it is water-soluble, it can be excreted in the urine. 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, delayed mental development, renal cysts, nephrocalcinosis and reduced bone density, among other symptoms. Recommended therapy includes drinking plenty of fluids and eating a low-purine diet. Xanthinuria can also develop as a result of drug treatment for gout with allopurinol. Allopurinol inhibits the enzyme xanthine oxidase to lower uric acid levels. Instead of increased uric acid formation, there is now an increase in xanthine concentration. To prevent kidney stone formation, fluid intake must be increased.
