|C 10 H 16 N 5 O 13 P 3
|External identifiers / databases
|507.18 g mol −1
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .
Adenosine triphosphate is the universal and immediately available energy carrier in cells and an important regulator of energy-supplying processes. The adenosine triphosphate molecule consists of an adenine residue , the sugar ribose and three phosphates (α to γ) in ester (α) or anhydride bonds (β and γ).
Adenosine triphosphate was discovered in 1929 by the German biochemist Karl Lohmann . A chemical synthesis of ATP was first published in 1949 by James Baddiley and Alexander Robertus Todd . The role as the main source of energy in cells was elucidated by Fritz Lipmann from 1939 to 1941 , after Vladimir Alexandrowitsch Engelhardt had shown in 1935 that ATP is necessary for muscle contractions, and Herman Moritz Kalckar had demonstrated the connection between cellular respiration and the biosynthesis of ATP in 1937. Subunits of the responsible ATP synthase were first isolated by Efraim Racker from 1960.
Processes in cells also need energy in order to perform chemical work such as the synthesis of organic molecules, osmotic work such as active substance transport through biomembrane and mechanical work such as muscle contraction . ATP is primarily used as a carrier of energy. The phosphate residues of this nucleoside triphosphate are connected to one another via phosphorus anhydride bonds ( acid anhydride bonds). One or two phosphate groups can be split off by enzyme-catalyzed hydrolysis and adenosine diphosphate (ADP) and monophosphate or adenosine monophosphate (AMP) and pyrophosphate are formed . When the phosphate bonds are cleaved, 32.3 kJ / mol when one bond is broken or 64.6 kJ / mol when both bonds are broken can be used for work under standard conditions .
ATP is a co- substrate of kinases , a group of phosphate-transferring enzymes that play a key role in metabolism and metabolic regulation . Important members of the latter group are the protein kinases , which, depending on their activation mechanism, are called protein kinase A (PKA, cAMP -dependent), protein kinase C (PKC, calcium -dependent), calmodulin -dependent kinase, or insulin-stimulated protein kinase (ISPK) to name just a few examples. Under blood sugar , some basic principles are addressed according to which a series of kinases can be interconnected to form an enzyme cascade .
ATP (like ADP and adenosine) is an agonist of purinergic receptors that play a role in both the central and peripheral nervous systems . It is therefore involved in processes such as blood flow regulation or the mediation of inflammatory reactions . It is released after neural injuries and can stimulate the proliferation of astrocytes and neurons .
The cell regenerates the ATP from the AMP or ADP created during the energy release from ATP. There are two different ways of doing this, called substrate chain phosphorylation and electron transport phosphorylation (respiratory chain).
In substrate chain phosphorylation , a phosphate residue is bound to an intermediate product from the breakdown of material energy sources and, after further reconstruction of the intermediate product, is transferred to ADP.
In electron transport phosphorylation, the transport of electrons along a redox gradient via various electron and hydrogen carriers in a membrane transports protons from one space in the cell enclosed by the membrane to another. In bacteria, protons are pumped outwards. In eukaryotes, these processes take place in the mitochondria . There protons are exported from the matrix of the mitochondrion into the intermembrane space . In both cases, a proton gradient is generated and used as the chemiosmotic potential ΔP , which is made up of a proton concentration difference ΔpH and an electrical potential difference ΔΨ. The reflux of the protons through the enzyme ATP synthase , which is also located in the membrane, drives the energy-consuming binding of inorganic phosphate residues to the ADP, which is catalyzed by this enzyme. In some organisms sodium ions are used instead of protons; they have an analogous Na + -dependent ATP synthase.
In chemotrophic organisms, the electrons are fed into the respiratory chain in the form of the reducing agents NADH , NADPH , FADH 2 or reduced ferredoxin . These come from the oxidative breakdown of high-energy compounds, such as carbohydrates or fatty acids. In aerobic organisms, the electrons are transferred to oxygen, which creates water. In the anaerobic respiration of other electron acceptors can be used, for example sulfur or iron (II). In both cases there is an electrochemical difference that is used to generate ATP. In eukaryotes the process takes place in the mitochondria , in prokaryotes in the cytoplasm.
In phototrophic organisms, after light is absorbed by chlorophylls, these electrons are given off at a high energy level. The light energy is used to generate an electrochemical difference. In green plants this takes place in the chloroplasts , in bacteria in the cytoplasm . Because of the use of light, one speaks in this case of photophosphorylation .
Short-term regeneration in muscle cells
Since oxidative phosphorylation is a relatively slow process in the respiratory chain, the ATP supply in heavily stressed cells (muscle cells) must be replenished at short notice. The ATP supply (approx. 6 mmol / kg muscle in the muscle cell) is only sufficient for about 2-3 seconds at maximum contraction. Molecules with a higher group transfer potential than ATP represent a reserve. Mammalian muscle cells keep a supply of creatine phosphate (21 mmol / kg muscle; 0.08% per body weight) ready. The creatine kinase catalyzes the transfer of phosphoryl from creatine phosphate to ADP. If this supply is used up after 6–10 seconds, the above-mentioned mechanisms must be responsible for the ATP regeneration alone.
Energy supply in muscle cells
During vigorous muscle exertion, muscle cells break down glucose to lactate in lactic acid fermentation in order to quickly produce ATP. Lactate itself is built up again in the liver to pyruvate and then to glucose with consumption of ATP ( gluconeogenesis ). This glucose is then made available to the muscle as an energy source. This cycle is also known as the Cori cycle .
In an emergency, the body's own proteins are also broken down to generate energy. Proteins are broken down into amino acids and these are mostly broken down into pyruvate. In a way similar to the Cori cycle, pyruvate is first transaminated to alanine and transported to the liver. There these steps are reversed and the liver produces glucose again from pyruvate, which is then made available to the muscles. This cycle is also known as the glucose-alanine cycle.
Energy supply in the heart muscle
The heart muscle uses fatty acids as fuel, these are broken down in the β-oxidation in the numerous mitochondria. Furthermore, glucose, lactate (via reoxidation to pyruvate), ketone bodies and glycogen can also be broken down. At high loads, up to 60% of the energy can be obtained from the oxidation of lactate.
The ATP concentration is a control variable in the cell : The drop below 4–5 mmol / l activates energy-supplying reactions (see phosphofructokinase ); exceeding the threshold causes energy storage, e.g. B. through the formation of creatine phosphate as quickly available (ATP-supplying) storage in the muscle or the formation of glycogen as an "energy cushion" in the liver. However, carbohydrate and protein stores are limited. Any excess energy leads to the storage of fat (via acetyl-CoA ).
In the average adult, the amount of ATP that is built up and broken down in his body every day is about half his body mass. A man weighing 80 kg converts around 40 kg of ATP per day, which corresponds to around 78.8 mol or 10 25 molecules that are newly formed. With intensive physical work, the ATP turnover can increase to 0.5 kg per minute.
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- HM Kalckar: Phosphorylation in Kidney Tissue . In: Enzymologia . 2, 1937, pp. 47-53.
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