Adenosine triphosphate or ATP is the most energy-rich molecule in the organism and is responsible for all energy-transferring processes. It is a mononucleotide of the purine base adenine and therefore also represents a building block of nucleic acids. Disturbances in the synthesis of ATP inhibit the release of energy and lead to states of exhaustion.
What is adenosine triphosphate?
Adenosine triphosphate (ATP) is a mononucleotide of adenine with three phosphate groups, each linked by an anhydride bond. ATP is the central molecule for the transfer of energy in the organism. The energy is mainly bound in the anhydride bond of the beta phosphate residue to the gamma phosphate residue. When a phosphate residue is removed to form adenosine diphosphate, energy is released. This energy is then used for energy-consuming processes. As a nucleotide, ATP consists of the purine base adenine, the sugar ribose and three phosphate residues. There is a glycosidic bond between adenine and ribose. Furthermore, the alphaphosphate residue is linked to ribose by an ester bond. An anhydride bond exists between alpha- beta- and gamma-phosphate. After the removal of two phosphates, the nucleotide adenosine monophosphate (AMP) is formed. This molecule is an important building block of RNA.
Function, action, and roles
Adenosine triphosphate performs multiple functions in the organism. Its most important function is the storage and transfer of energy. All processes in the body involve energy transfers and energy transformations. Thus, the organism must perform chemical, osmotic or mechanical work. For all these processes, ATP quickly provides energy. ATP is a short-term energy store, which is quickly depleted and therefore must be synthesized again and again. The majority of energy-consuming processes represent transport processes within the cell and out of the cell. In these processes, biomolecules are transported to the sites of their reaction and conversion. Anabolic processes such as protein synthesis or the formation of body fat also require ATP as an energy-transferring agent. Molecule transports across the cell membrane or the membranes of various cell organelles are also energy dependent. Furthermore, the mechanical energy for muscle contractions can only be provided by the action of ATP from energy supplying processes. In addition to its function as an energy carrier, ATP is also an important signaling molecule. It acts as a cosubstrate for the so-called kinases. Kinases are enzymes that transfer phosphate groups to other molecules. These are mainly protein kinases that influence the activity of various enzymes by phosphorylating them. Extracellularly, ATP is an agonist of receptors of cells of the peripheral and central nervous system. Thus, it participates in the regulation of blood flow and the initiation of inflammatory responses. When nervous tissue is injured, it is released in greater amounts to mediate increased formation of astrocytes and neurons.
Formation, occurrence, properties, and optimal levels
Adenosine triphosphate is only a short-term energy store and is depleted within seconds during energy-consuming processes. Therefore, its constant regeneration is a vital task. The molecule plays such a central role that ATP with a mass of half the body weight is produced within one day. In this process, adenosine diphosphate is transformed into adenosine triphosphate by an additional binding with phosphate under energy consumption, which immediately provides energy again by splitting off the phosphate under reconversion into ADP. Two different reaction principles are available for the regeneration of ATP. One principle is substrate chain phosphorylation. In this reaction, a phosphate residue is transferred directly to an intermediate molecule in an energy-supplying process, which is immediately transferred to ADP with the formation of ATP. A second reaction principle is part of the respiratory chain as electron transport phosphorylation. This reaction takes place only in the mitochondria. As part of this process, an electrical potential is established through the membrane via various proton transporting reactions. The reflux of protons results in the formation of ATP from ADP with the release of energy. This reaction is catalyzed by the enzyme ATP synthetase.Overall, these regeneration processes are still too slow for some requirements. During muscle contraction, for example, all supplies of ATP are used up after two to three seconds. For this purpose, energy-rich creatine phosphate is available in muscle cells, which immediately makes its phosphate available for the formation of ATP from ADP. This supply is now exhausted after six to ten seconds. After that, the general regeneration processes must come into play again. However, due to the effect of creatine phosphate, it is possible to extend muscle training somewhat without premature exhaustion.
Diseases and disorders
When too little adenosine triphosphate is produced, fatigue conditions occur. ATP is synthesized mainly in mitochondria via electron transport phosphorylation. When mitochondrial function is impaired, the production of ATP is also reduced. For example, studies have found that patients with chronic fatigue syndrome (CFS) had decreased ATP concentrations. This decreased production of ATP always correlated with disorders in the mitochondria (mitochondriopathies). Causes of mitochondriopathies included cellular hypoxia, infections with EBV, fibromyalgias, or chronic degenerative inflammatory processes. There are both genetic and acquired disorders of mitochondria. Thus, about 150 different diseases have been described which lead to mitochondriopathy. These include diabetes mellitus, allergies, autoimmune diseases, dementia, chronic inflammation or immunodeficiency diseases. The states of exhaustion in the context of these diseases are caused by a lower energy supply due to the reduced production of ATP. As a result, disorders of mitochondrial function can lead to multiorgan diseases.
