Adenine is a heterobicyclic aromatic compound with a purine backbone that, as an organic nucleic base, forms one of the basic building blocks of genetic information in DNA and RNA along with three other bases. In addition, adenine in the form of a nucleoside or nucleotide plays an important role in metabolism as NAD, FADH2 or ATP, especially in the energy balance of cells, in the mitochondria.
What is adenine?
Adenine, with the chemical molecular formula C5N5H5, consists of a heterobicyclic aromatic ring (purine backbone) with an attached amino group (NH2). Adenine is therefore also known as aminopurine. It is a pale yellow solid that sublimates at 220 degrees Celsius, i.e. passes directly into the gaseous state, and is only poorly soluble in water. Through the addition of a deoxyribose sugar molecule, deoxyadenosine is formed from adenine, one of the 4 building blocks that make up the double helix DNA. The complementary base is deoxythymidine, which is formed from thymidine and the deoxyribose molecule that is also attached. In the case of RNA, the process is slightly modified. Adenine becomes adenosine by attachment of a D-ribose sugar molecule. The adenosine takes the position of the deoxyadenosine of the DNA in the RNA. The complementary base is now not thymine, but uracil in the form of uridine. In addition, adenosine forms the backbone of the nucleotides ATP, ADP and AMP, which assume an important function in the energy balance of cells. Adenosine also performs important roles as a cofactor in a number of enzymes, hormones, and neuromodulators such as coenzyme A, NADPH, and NADH.
Function, effects, and roles
As a component of one strand of the DNA double helix, adenosine forms the base pair adenine-thymine (A-T) via two hydrogen bonds with the complementary nucleic base thymine in the form of deoxythymidine. In RNA, which is usually single-stranded, adenine has an analogous function, but in the formation of the complementary strand, the mRNA (messenger RNA), the complementary base is not thymidine but uracil. As a component of DNA and RNA, adenine is not directly involved in metabolic processes, but only serves in combination with the other nucleic bases to encode amino acid sequences for the synthesis of the corresponding proteins. A part of the energy metabolism of almost all cells, called the respiratory chain, essentially consists of a series of oxidation and reduction processes, so-called redox processes. Within the respiratory chain, adenosine, which is phosphorylated to adenosine triphosphate (ATP), plays a central role. ATP releases a phosphorus group and thus becomes adensoindiphosphate (ADP) or adenosine monophosphate (AMP). Overall, this is an exothermic process that provides energy for metabolism and, for example, for muscle work via the breakdown of carbohydrates. In this function, adenine or adenosine is directly involved in chemical conversions. An important dynamic component in the chain of redox reactions also includes electron transfer from electrons bound to hydrogen (H) or other electron carriers. Again, adenine and adenosine are functional components of enzymes or catalysts such as nicotinic diamide (NAD) and others that ultimately break down the oxidation (combustion) of hydrogen to water into many catalytically controlled individual steps, thus making them available to metabolism without causing combustion damage.
Formation, occurrence, properties, and optimum values
According to the chemical molecular formula C5N5H5, adenine thus consists of the basic building blocks carbon, nitrogen and hydrogen, all of which are abundant in nature. Rare trace elements or minerals are not necessary. Accordingly, there is no need to fear a shortage of basic materials for synthesis, but at most a problem in the body’s own production process. Since synthesis is costly and energy-intensive, the body uses a different pathway for about 90% of its production; it synthesizes adenine by recycling. In the course of purine metabolism, adenine is obtained as a degradation product from more complex compounds. Biochemically, adenine becomes active only as a nucleoside through the addition of a molecule of deoxyribose. Adenine is thereby transformed into deoxyadenosine. With a further addition of one to three phosphate residues, the deoxyadenosine becomes a nucleotide called adenosine monophosphate (AMP), cyclic adenosine monophosphate (cAMP), adenosine diphosphate (ADP), or adenosine triphosphate (ATP).In accordance with the diverse tasks of adenine and its biochemically active manifestations in an environment that corresponds to dynamically changing requirements, and free adenine does not occur in the systemic circulation, any level of adenine cannot be measured. Conclusions about an intact purine metabolism can only be drawn indirectly by observing and measuring certain metabolic processes.
Diseases and disorders
The best-known – but de facto rare – metabolic disorder that occurs in connection with the endogenous formation of adenine and its bioactive forms is Lesch-Nyhan syndrome. It is a gene defect on the x chromosome. The gene mutation results in a complete deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGPRT). The absence of HGPRT leads to a disruption in purine metabolism, eliminating the recycling of the purine bases hypoxanthine and guanine that normally occurs. Instead, the body is forced to continuously produce adenine via neosynthesis. This leads to excessive amounts of uric acid and precipitation of uric acid crystals, which can cause gout or the formation of urinary stones in the joints. In addition, newborns typically experience mental developmental deficits and increased autoaggression. Another rare hereditary disease is Huntington’s disease. Here, a genetic defect is present on chromosome 4. Normally, the base sequence cytosine-adenine-guanine with 10 to 30 repeats is found there in a specific gene. If, due to a gene mutation, there are more than 36 of these so-called triplet repeats, the hereditary disease Huntington’s disease occurs. As the disease progresses, motor problems and nerve damage occur and there is no cure.
