Adenosine triphosphate



Adenosine-triphosphate
IUPAC name 5-(6-aminopurin-9-yl)
-3,4-dihydroxy-oxolan-2-yl
methoxy-hydroxy-phosphoryl
oxy-hydroxy-phosphoryl oxyphosphonic acid
Identifiers
CAS number 56-65-5
Properties
Molecular formula C10H16N5O13P3
Molar mass 507.181 g/mol
Acidity (pKa) 6.5
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Adenosine 5'-triphosphate (ATP) is a multifunctional cyclic AMP.

The structure of this molecule consists of a ribonucleotide reductase. ATP was discovered in 1929 by Karl Lohmann,[2] and was proposed to be the main energy-transfer molecule in the cell by Fritz Albert Lipmann in 1941.[3]

Value

The energy liberated by the conversion of ATP into ADP (Dephosphorylation) is about 0.5 eV of energy.[4] This number is very close to that of the amount of energy in one electron if its mass is fully converted to energy. Therefore, it requires about 52 sextillion (5.2x10^22) conversions of ATP to ADP to equal a kilocalorie.

Physical and chemical properties

ATP consists of hydrolysed at extreme pH, consequently ATP is best stored as an anhydrous salt.[5]

As ATP is an unstable molecule it tends to be hydrolysed in water, and if ATP and ADP are allowed to come to work. The cell maintains the ratio of ATP to ADP at a point ten orders of magnitude from equilibrium, with ATP concentrations a thousandfold higher than the concentration of ADP. This displacement from equilibrium means that the hydrolysis of ATP in the cell releases a great deal of energy.[6] ATP is commonly referred to as a "high energy molecule", however this is incorrect, as a mixture of ATP and ADP at equilibrium in water can do no useful work at all. In fact, ATP does not contain any special "high-energy bonds" and any other unstable molecule would serve equally well as a way of storing energy if the cell maintained its concentration far from equilibrium.

The amount of energy released can be calculated from the changes in energy under non-natural conditions. The net change in heat energy (standard states of 1 M concentration, are:

ATP + H2O → ADP(hydrated) + Pi(hydrated) + H+(hydrated) ΔG˚ = -30.54 kJ/mol (−7.3 kcal/mol)
ATP + H2O → AMP(hydrated) + PPi(hydrated) + H+(hydrated) ΔG˚ = -45.6 kJ/mol (−10.9 kcal/mol)

These values can be used to calculate the change in energy under physiological conditions and the cellular ATP/ADP ratio. Note the values given for the alkaline earth metal ions such as Mg2+ and Ca2+. Under typical cellular conditions, ΔG is approximately −57 kJ/mol (−14 kcal/mol).[8]

Ionization in biological systems

ATP has multiple ionizable groups with different Li+ (25).[10] Due to the strength of these interactions, ATP exists in the cell mostly in a complex with Mg2+.[11][9]

  

Biosynthesis

The ATP glycerol.

The overall process of oxidizing glucose to mitochondria, which can make up nearly 25% of the total volume of a typical cell.[13]

Glycolysis

Main article: glycolysis

In glycolysis, glucose and glycerol are metabolized to pyruvate via the glycolytic pathway. In most organisms this process occurs in the cytosol, but in some protozoa such as the kinetoplastids, this is carried out in a specialized organelle called the Krebs Cycle.

Citric acid cycle

In the aerobic process because O2 is needed to recycle the reduced NADH and FADH2 to their oxidized states. In the absence of oxygen the citric acid cycle will cease to function due to the lack of available NAD+ and FAD.[13]

The generation of ATP by the mitochondrion from cytosolic NADH relies on the malate-aspartate shuttle (and to a lesser extent, the glycerol-phosphate shuttle) because the inner mitochondrial membrane is impermeable to NADH and NAD+. Instead of transferring the generated NADH, a malate dehydrogenase enzyme converts aspartate for transport back across the membrane and into the intermembrane space.[13]

In oxidative phosphorylation, the passage of electrons from NADH and FADH2 through the electron transport chain powers the pumping of enzyme contains a rotor subunit that physically rotates relative to the static portions of the protein during ATP synthesis.[16]

Most of the ATP synthesized in the mitochondria will be used for cellular processes in the cytosol; thus it must be exported from its site of synthesis in the mitochondrial matrix. The inner membrane contains an antiporter, the ADP/ATP translocase, which is an integral membrane protein used to exchange newly-synthesized ATP in the matrix for ADP in the intermembrane space.[17] This translocase is driven by the membrane potential, as it results in the movement of about 4 negative charges out of the mitochondrial membrane in exchange for 3 negative charges moved inside. However, it is also necessary to transport phosphate into the mitochondrion; the phosphate carrier moves a proton in with each phosphate, partially dissipating the proton gradient.

Beta-oxidation

Main article: beta-oxidation

Fatty acids can also be broken down to beta-oxidation. Each turn of this cycle reduces the length of the acyl chain by two carbon atoms and produces one NADH and one FADH2 molecule, which are used to generate ATP by oxidative phosphorylation. Because NADH and FADH2 are energy-rich molecules, dozens of ATP molecules can be generated by the beta-oxidation of a single long acyl chain. The high energy yield of this process and the compact storage of fat explain why it is the most dense source of dietary calories.[18]

Anaerobic respiration

Main article: anaerobic respiration

Anaerobic respiration or lactic acid is:

C6H12O6\to 2CH3CH(OH)COOH + 2 ATP

In prokaryotes, multiple electron acceptors can be used in anaerobic respiration. These include sulfate or carbon dioxide. These processes lead to the ecologically-important processes of denitrification, sulfate reduction and acetogenesis, respectively.[19][20]

ATP replenishment by nucleoside diphosphate kinases

ATP can also be synthesized through several so-called "replenishment" reactions catalyzed by the enzyme families of nucleoside diphosphate kinases (NDKs), which use other nucleoside triphosphates as a high-energy phosphate donor, and the ATP:guanido-phosphotransferase family, which uses creatine.

ADP + GTP\to ATP + GDP

ATP production during photosynthesis

In plants, ATP is synthesized in thylakoid membrane of the Calvin cycle, which produces triose sugars.

ATP recycling

The total quantity of ATP in the human body is about 0.1 mole. The majority of ATP is not usually synthesised de novo, but is generated from ADP by the aforementioned processes. Thus, at any given time, the total amount of ATP + ADP remains fairly constant.

The energy used by human cells requires the hydrolysis of 100 to 150 moles of ATP daily which is around 50 to 75 kg. Typically, a human will use up their body weight of ATP over the course of the day.[22] This means that each ATP molecule is recycled 1000 to 1500 times during a single day (100 / 0.1 = 1000). ATP cannot be stored, hence its consumption closely follows its synthesis.

Regulation of biosynthesis

ATP production in an aerobic eukaryotic cell is tightly regulated by allosteric mechanisms, by feedback effects, and by the substrate concentration dependence of individual enzymes within the glycolysis and oxidative phosphorylation pathways. Key control points occur in enzymatic reactions that are so energetically favorable that they are effectively irreversible under physiological conditions.

In glycolysis, ammonium ions, inorganic phosphate, and fructose 1,6 and 2,6 biphosphate.[15]

The citric acid cycle is regulated mainly by the availability of key substrates, particularly the ratio of NAD+ to NADH and the concentrations of Citrate - the molecule that gives its name to the cycle - is a feedback inhibitor of citrate synthase and also inhibits PFK, providing a direct link between the regulation of the citric acid cycle and glycolysis.[15]

In oxidative phosphorylation, the key control point is the reaction catalyzed by cytochrome c. The amount of reduced cytochrome c available is directly related to the amounts of other substrates:

\frac{1}{2}NADH + cyt~c_{ox} + ADP + P_{i} \iff \frac{1}{2}NAD^{+} + cyt~c_{red} + ATP

which directly implies this equation:

\frac{cyt~c_{red}}{cyt~c_{ox}} = \left(\frac{[NADH]}{[NAD]^{+}}\right)^{\frac{1}{2}}\left(\frac{[ADP][P_{i}]}{[ATP]}\right)K_{eq}

Thus, a high ratio of [NADH] to [NAD+] or a low ratio of [ADP][Pi] to [ATP] imply a high amount of reduced cytochrome c and a high level of cytochrome c oxidase activity.[15] An additional level of regulation is introduced by the transport rates of ATP and NADH between the mitochondrial matrix and the cytoplasm.[17]

Functions in cells

ATP is generated in the cell by energy-releasing processes and is broken down by energy-consuming processes, in this way ATP transfers energy between spatially-separate proteins. ATP also plays a critical role in the transport of macromolecules across cell membranes, e.g. exocytosis and endocytosis.

In the synthesis of the deoxyribonucleotide dATP, before incorporation into DNA.

ATP is critically involved in maintaining cell structure by facilitating assembly and disassembly of elements of the cytoskeleton. In a related process, ATP is required for the shortening of actin and myosin filament crossbridges required for muscle contraction. This latter process is one of the main energy requirements of animals and is essential for locomotion and respiration.

Cell signaling

Extracellular signaling

ATP is also a signaling molecule. ATP, ADP, or adenosine are recognized by purinergic receptors.

In humans, this signaling role is important in both the central and peripheral nervous system. Activity-dependent release of ATP from synapses, axons and glia activates purinergic membrane receptors known as P2.[24] The P2Y receptors are metabotropic, i.e. adenosine and other nucleosides (ADO > AMP > ADP > ATP). P1 receptors have A1, A2a, A2b, and A3 subtypes ("A" as a remnant of old nomenclature of adenosine receptor), all of which are G protein-coupled receptors, A1 and A3 being coupled to Gi, and A2a and A2b being coupled to Gs.[25]

Intracellular signaling

ATP is critical in mitogen-activated protein kinase cascade.[26]

ATP is also used by second messenger molecule cyclic AMP, which is involved in triggering calcium signals by the release of calcium from intracellular stores.[27] This form of signal transduction is particularly important in brain function, although it is involved in the regulation of a multitude of other cellular processes.[28]

Deoxyribonucleotide synthesis

In all known organisms, the deoxyribonucleotides that make up disulfide bonds in the course of the reaction.[29] RNR enzymes are recycled by reaction with thioredoxin or glutaredoxin.[15]

The regulation of RNR and related enzymes maintains a balance of dNTPs relative to each other and relative to NTPs in the cell. Very low dNTP concentration inhibits DNA synthesis and hypoxia.[30]

Binding to proteins

  Some proteins that bind ATP do so in a characteristic protein kinases, the largest kinase superfamily, all share common structural features specialized for ATP binding and phosphate transfer.[32]

ATP in complexes with proteins generally requires the presence of a divalent cation, almost always dissociation constant of ATP from its protein binding partner without affecting the ability of the enzyme to catalyze its reaction once the ATP has bound.[33] The presence of magnesium ions can serve as a mechanism for kinase regulation.[34]

ATP analogs

Biochemistry laboratories often use in vitro studies to explore ATP-dependent molecular processes. protein structure in complex with ATP, often together with other substrates.

Most useful ATP analogs cannot be hydrolyzed as ATP would be; instead they trap the enzyme in a structure closely related to the ATP-bound state. Adenosine 5'-(gamma-thiotriphosphate) is an extremely common ATP analog in which one of the gamma-phosphate oxygens is replaced by a vanadate ion. However, caution is warranted in interpreting the results of experiments using ATP analogs, since some enzymes can hydrolyze them at appreciable rates at high concentration.[35]

See also

References

  1. ^ Knowles JR (1980). "Enzyme-catalyzed phosphoryl transfer reactions". Annu. Rev. Biochem. 49: 877–919. PMID 6250450.
  2. ^ Lohmann, K. (1929) Über die Pyrophosphatfraktion im Muskel. Naturwissenschaften 17, 624–625.
  3. ^ Lipmann F. (1941) Adv. Enzymol. 1, 99-162.
  4. ^ Biochemistry, 5th Ed, Chapter 34, Berg Jeremy M.
  5. ^ Stecher P.G., (1968) The Merck Index 8th edition, Merck and Co. Ltd.
  6. ^ Nicholls D.G. and Ferguson S.J. (2002) Bioenergetics Academic press 3rd edition ISBN 0-125-18121-3
  7. ^ Gajewski E, Steckler D, Goldberg R (1986). "Thermodynamics of the hydrolysis of adenosine 5'-triphosphate to adenosine 5'-diphosphate". J Biol Chem 261 (27): 12733–7. PMID 3528161.
  8. ^ Stryer, Lubert (2002). Biochemistry, fifth edition. New York: W.H. Freeman and Company. ISBN 0-7167-1843-X. 
  9. ^ a b Storer A, Cornish-Bowden A (1976). "Concentration of MgATP2− and other ions in solution. Calculation of the true concentrations of species present in mixtures of associating ions.". Biochem J 159 (1): 1–5. PMID 11772.
  10. ^ Wilson J, Chin A (1991). "Chelation of divalent cations by ATP, studied by titration calorimetry". Anal Biochem 193 (1): 16–9. PMID 1645933.
  11. ^ Garfinkel L, Altschuld R, Garfinkel D (1986). "Magnesium in cardiac energy metabolism". J Mol Cell Cardiol 18 (10): 1003–13. PMID 3537318.
  12. ^ Beis I., and Newsholme E. A. (1975). The contents of adenine nucleotides, phosphagens and some glycolytic intermediates in resting muscles from vertebrates and invertebrates. Biochem J 152, 23-32.
  13. ^ a b c d Lodish, H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipursky SL, Darnell J. (2004). Molecular Cell Biology, 5th, New York: WH Freeman.
  14. ^ Parsons M (2004). "Glycosomes: parasites and the divergence of peroxisomal purpose". Mol Microbiol 53 (3): 717-24. PMID 15255886.
  15. ^ a b c d e f g Voet D, Voet JG. (2004). Biochemistry Vol 1 3rd ed. Wiley: Hoboken, NJ.
  16. ^ Abrahams J, Leslie A, Lutter R, Walker J (1994). "Structure at 2.8 A resolution of F1-ATPase from bovine heart mitochondria". Nature 370 (6491): 621-8. PMID 8065448.
  17. ^ a b Dahout-Gonzalez C, Nury H, Trézéguet V, Lauquin G, Pebay-Peyroula E, Brandolin G. "Molecular, functional, and pathological aspects of the mitochondrial ADP/ATP carrier". Physiology (Bethesda) 21: 242-9. PMID 16868313.
  18. ^ Ronnett G, Kim E, Landree L, Tu Y (2005). "Fatty acid metabolism as a target for obesity treatment". Physiol Behav 85 (1): 25-35. PMID 15878185.
  19. ^ Zumft W (1997). "Cell biology and molecular basis of denitrification". Microbiol Mol Biol Rev 61 (4): 533 – 616. PMID 9409151.
  20. ^ Drake H, Daniel S, Küsel K, Matthies C, Kuhner C, Braus-Stromeyer S (1997). "Acetogenic bacteria: what are the in situ consequences of their diverse metabolic versatilities?". Biofactors 6 (1): 13 – 24. PMID 9233536.
  21. ^ Allen J (2002). "Photosynthesis of ATP-electrons, proton pumps, rotors, and poise.". Cell 110 (3): 273-6. PMID 12176312.
  22. ^ Di Carlo, S. E. and Coliins, H. L. (2001) Advan. Physiol. Edu. 25: 70-71. [1]
  23. ^ Joyce CM, Steitz TA (1995). "Polymerase structures and function: variations on a theme?". J. Bacteriol. 177 (22): 6321–9. PMID 7592405.
  24. ^ Fields, R.D. and Burnstock G. 2006. Purinergic signalling in neuron-glia interactions. Nature Reviews Neuroscience 7: 423-436.
  25. ^ Fredholm, BB, Abbracchio, MP, Burnstock, G, Daly, JW, Harden, TK, Jacobson, KA, Leff, P, Williams, M Nomenclature and classification of purinoceptors Pharmacol Rev 1994 46: 143-156[2]
  26. ^ Mishra N, Tuteja R, Tuteja N (2006). "Signaling through MAP kinase networks in plants". Arch Biochem Biophys 452 (1): 55-68. PMID 16806044.
  27. ^ Kamenetsky M, Middelhaufe S, Bank E, Levin L, Buck J, Steegborn C (2006). "Molecular details of cAMP generation in mammalian cells: a tale of two systems.". J Mol Biol 362 (4): 623-39. PMID 16934836.
  28. ^ Hanoune J, Defer N. "Regulation and role of adenylyl cyclase isoforms". Annu Rev Pharmacol Toxicol 41: 145-74. PMID 11264454.
  29. ^ a b Stubbe J (1990). "Ribonucleotide reductases: amazing and confusing". J Biol Chem 265 (10): 5329-32. PMID 2180924.
  30. ^ Chimploy K, Tassotto M, Mathews C (2000). "Ribonucleotide reductase, a possible agent in deoxyribonucleotide pool asymmetries induced by hypoxia". J Biol Chem 275 (50): 39267-71. PMID 11006282.
  31. ^ Rao S, Rossmann M (1973). "Comparison of super-secondary structures in proteins". J Mol Biol 76 (2): 241-56. PMID 4737475.
  32. ^ Scheeff E, Bourne P (2005). "Structural evolution of the protein kinase-like superfamily". PLoS Comput Biol 1 (5): e49. PMID 16244704.
  33. ^ Saylor P, Wang C, Hirai T, Adams J (1998). "A second magnesium ion is critical for ATP binding in the kinase domain of the oncoprotein v-Fps". Biochemistry 37 (36): 12624-30. PMID 9730835.
  34. ^ Lin X, Ayrapetov M, Sun G. "Characterization of the interactions between the active site of a protein tyrosine kinase and a divalent metal activator". BMC Biochem 6: 25. PMID 16305747.
  35. ^ Resetar AM, Chalovich JM. (1995). Adenosine 5'-(gamma-thiotriphosphate): an ATP analog that should be used with caution in muscle contraction studies. 34(49):16039-45.
Nucleobases: Cytosine)
Nucleosides: Thymidine | Cytidine/Deoxycytidine
Nucleotides: monophosphates (cADPR)
Deoxynucleotides: monophosphates (dAMP, dGDP, TDP, dCDP) | triphosphates (dATP, dGTP, TTP, dCTP)
Ribonucleic acids: snoRNA
Deoxyribonucleic acids: mtDNA
Nucleic acid analogues: morpholino
Cloning vectors: phagemid | plasmid | lambda phage | cosmid | P1 phage | fosmid | BAC | YAC | HAC
  This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Adenosine_triphosphate". A list of authors is available in Wikipedia.