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[[Image:ATP chemical structure.png|thumb|[[Adenosine triphosphate]]]]
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[[Image:ADP chemical structure.png|thumb|[[Adenosine diphosphate]]]]
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'''ATPases''' are a class of [[enzyme]]s that [[catalysis|catalyze]] the [[decomposition]] of [[adenosine triphosphate]] (ATP) into [[adenosine diphosphate]] (ADP) and a free [[phosphate]] [[ion]]. This [[dephosphorylation]] reaction releases [[energy]], which the enzyme (in most cases) harnesses to drive other [[chemical reaction]]s that would not otherwise occur. This process is widely used in all known forms of [[life]].
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Some such enzymes are [[integral membrane protein]]s (anchored within [[biological membrane]]s), and move [[solute]]s across the membrane. (These are called ''transmembrane ATPases'').
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==Functions==
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[[Image:Sodium-Potassium pump.svg|thumb|250px|[[NaKATPase|Na<sup>+</sup>/K<sup>+</sup>ATPase]] ]]
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Transmembrane ATPases import many of the metabolites necessary for [[cell (biology)|cell]] [[metabolism]] and export toxins, wastes, and solutes that can hinder cellular processes. An important example is the sodium-potassium exchanger (or [[NaKATPase|Na<sup>+</sup>/K<sup>+</sup>ATPase]]), which establishes the ionic concentration balance that maintains the [[cell potential]]. Another example is the [[hydrogen potassium ATPase]] (H<sup>+</sup>/K<sup>+</sup>ATPase or gastric proton pump) that acidifies the contents of the stomach.
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Besides exchangers, other categories of transmembrane ATPase include [[co-transport]]ers and pumps (however, some exchangers are also pumps). Some of these, like the Na<sup>+</sup>/K<sup>+</sup>ATPase, cause a net flow of charge, but others do not. These are called "electrogenic" and "nonelectrogenic" transporters, respectively.
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==Mechanism==
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The coupling between ATP hydrolysis and transport is more or less a strict chemical reaction, in which a fixed number of solute molecules are transported for each ATP molecule that is hydrolyzed; for example, 3 Na<sup>+</sup> ions out of the cell and 2 K<sup>+</sup> ions inward per ATP hydrolyzed, for the Na<sup>+</sup>/K<sup>+</sup> exchanger.
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Transmembrane ATPases harness the chemical potential energy of ATP, because they perform [[mechanical work]]: they transport solutes in a direction opposite to their [[thermodynamic|thermodynamically]] preferred direction of movement&mdash;that is, from the side of the membrane where they are in low concentration to the side where they are in high concentration. This process is considered [[active transport]].
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For example, the blocking of the vesicular H+-ATPAses would increase the pH inside vesicles and decrease the pH of the cytoplasm.
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==ATP synthase==
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The [[ATP synthase]] of [[mitochondria]] and [[chloroplast]]s is an [[Anabolism|anabolic]] enzyme that harnesses the energy of a transmembrane [[proton]] gradient as an energy source for adding an [[inorganic phosphate]] group to a molecule of [[adenosine diphosphate]] (ADP) to form a molecule of adenosine triphosphate (ATP).
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This enzyme works when a proton moves down the concentration gradient, giving the enzyme a spinning motion. This unique spinning motion bonds ADP and P together to create ATP.
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ATP synthase can also function in reverse, that is, use energy released by ATP hydrolysis to pump protons against their thermodynamic gradient.
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==Human genes==
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* [[Na+/K+-ATPase|Na+/K+ transporting]]: {{Gene|ATP1A1}}, {{Gene|ATP1A2}}, {{Gene|ATP1A3}}, {{Gene|ATP1A4}}, {{Gene|ATP1B1}}, {{Gene|ATP1B2}}, {{Gene|ATP1B3}}, {{Gene|ATP1B4}}
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* [[Calcium ATPase|Ca++ transporting]]: {{Gene|ATP2A1}}, {{Gene|ATP2A2}}, {{Gene|ATP2A3}}, {{Gene|ATP2B1}}, {{Gene|ATP2B2}}, {{Gene|ATP2B3}}, {{Gene|ATP2B4}}, {{Gene|ATP2C1}}
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* Mg++ transporting: {{Gene|ATP3}}
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* [[Hydrogen potassium ATPase|H+/K+ exchanging]]: {{Gene|ATP4A}}, {{Gene|ATP4B}}
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* H+ transporting, mitochondrial: {{Gene|ATP5A1}}, {{Gene|ATP5B}}, {{Gene|ATP5C1}}, {{Gene|ATP5C2}}, {{Gene|ATP5D}}, {{Gene|ATP5E}}, {{Gene|ATP5F1}}, {{Gene|ATP5G1}}, {{Gene|ATP5G2}}, {{Gene|ATP5G3}}, {{Gene|ATP5H}}, {{Gene|ATP5I}}, {{Gene|ATP5J}}, {{Gene|ATP5J2}}, {{Gene|ATP5L}}, {{Gene|ATP5L2}}, {{Gene|ATP5O}}, {{Gene|ATP5S}}
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* [[V-ATPase|H+ transporting, lysosomal]]: {{Gene|ATP6AP1}}, {{Gene|ATP6AP2}}, {{Gene|ATP6V1A}}, {{Gene|ATP6V1B1}}, {{Gene|ATP6V1B2}}, {{Gene|ATP6V1C1}}, {{Gene|ATP6V1C2}}, {{Gene|ATP6V1D}}, {{Gene|ATP6V1E1}}, {{Gene|ATP6V1E2}}, {{Gene|ATP6V1F}}, {{Gene|ATP6V1G1}}, {{Gene|ATP6V1G2}}, {{Gene|ATP6V1G3}}, {{Gene|ATP6V1H}}, {{Gene|ATP6V0A1}}, {{Gene|ATP6V0A2}}, {{Gene|ATP6V0A4}}, {{Gene|ATP6V0B}}, {{Gene|ATP6V0C}}, {{Gene|ATP6V0D1}}, {{Gene|ATP6V0D2}}, {{Gene|ATP6V0E}}
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* Cu++ transporting: {{Gene|ATP7A}} (see also [[ATP7A]]), {{Gene|ATP7B}}
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* Class I, type 8: {{Gene|ATP8A1}}, {{Gene|ATP8B1}}, {{Gene|ATP8B2}}, {{Gene|ATP8B3}}, {{Gene|ATP8B4}}
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* Class II, type 9: {{Gene|ATP9A}}, {{Gene|ATP9B}}
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* Class V, type 10: {{Gene|ATP10A}}, {{Gene|ATP10B}}, {{Gene|ATP10D}}
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* Class VI, type 11: {{Gene|ATP11A}}, {{Gene|ATP11B}}, {{Gene|ATP11C}}
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* H+/K+ transporting, nongastric: {{Gene|ATP12A}}
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* type 13: {{Gene|ATP13A1}}, {{Gene|ATP13A2}}, {{Gene|ATP13A3}}, {{Gene|ATP13A4}}, {{Gene|ATP13A5}}
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==See also==
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[[AAA proteins]]
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==Additional images==
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<gallery>
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Image:AAA+ ATPases (three examples).png|AAA+ ATPases (three examples)
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</gallery>
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==External links==
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*[http://www.biologie.uni-osnabrueck.de/biophysik/Feniouk/Home.html "ATP synthase - a splendid molecular machine"]
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* {{MeshName|ATPase}}
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* {{UMichOPM|families|superfamily|5}} - Proton or sodium translocating F- and V-type ATPases
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* {{UMichOPM|families|superfamily|22}} - Different conformations of P-type ATPase
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{{Ion pumps}}
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{{Acid anhydride hydrolases}}
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{{ATPases}}
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[[Category:EC 3.6.3]]
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[[Category:Integral membrane proteins]]
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{{enWP|ATPase}}

Latest revision as of 06:04, August 24, 2007

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ATP chemical structure
Adenosine triphosphate
PhloxBotAdded by PhloxBot
ADP chemical structure
Adenosine diphosphate
PhloxBotAdded by PhloxBot

ATPases are a class of enzymes that catalyze the decomposition of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and a free phosphate ion. This dephosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life.

Some such enzymes are integral membrane proteins (anchored within biological membranes), and move solutes across the membrane. (These are called transmembrane ATPases).

Contents

FunctionsEdit

Sodium-Potassium pump
Na+/K+ATPase
Dr Joe KiffAdded by Dr Joe Kiff

Transmembrane ATPases import many of the metabolites necessary for cell metabolism and export toxins, wastes, and solutes that can hinder cellular processes. An important example is the sodium-potassium exchanger (or Na+/K+ATPase), which establishes the ionic concentration balance that maintains the cell potential. Another example is the hydrogen potassium ATPase (H+/K+ATPase or gastric proton pump) that acidifies the contents of the stomach.

Besides exchangers, other categories of transmembrane ATPase include co-transporters and pumps (however, some exchangers are also pumps). Some of these, like the Na+/K+ATPase, cause a net flow of charge, but others do not. These are called "electrogenic" and "nonelectrogenic" transporters, respectively.

MechanismEdit

The coupling between ATP hydrolysis and transport is more or less a strict chemical reaction, in which a fixed number of solute molecules are transported for each ATP molecule that is hydrolyzed; for example, 3 Na+ ions out of the cell and 2 K+ ions inward per ATP hydrolyzed, for the Na+/K+ exchanger.

Transmembrane ATPases harness the chemical potential energy of ATP, because they perform mechanical work: they transport solutes in a direction opposite to their thermodynamically preferred direction of movement—that is, from the side of the membrane where they are in low concentration to the side where they are in high concentration. This process is considered active transport.

For example, the blocking of the vesicular H+-ATPAses would increase the pH inside vesicles and decrease the pH of the cytoplasm.

ATP synthaseEdit

The ATP synthase of mitochondria and chloroplasts is an anabolic enzyme that harnesses the energy of a transmembrane proton gradient as an energy source for adding an inorganic phosphate group to a molecule of adenosine diphosphate (ADP) to form a molecule of adenosine triphosphate (ATP).

This enzyme works when a proton moves down the concentration gradient, giving the enzyme a spinning motion. This unique spinning motion bonds ADP and P together to create ATP.

ATP synthase can also function in reverse, that is, use energy released by ATP hydrolysis to pump protons against their thermodynamic gradient.

Human genesEdit

See alsoEdit

AAA proteins

Additional imagesEdit

External linksEdit

-  Proton or sodium translocating F- and V-type ATPases

- Different conformations of P-type ATPase
Membrane transport protein: ion pumps

Uniporter - Cotransporter

Symporter: Na+/K+/2Cl- - Na/Pi3 - Na+/Cl- - Na/glucose

Antiporter (exchanger): Na+/H+ - Na+/Ca2+ - Cl-/HCO3- (Band 3)

ATPase: F - V - H/K+ - Na+/K+ - Ca+ (SERCA, Plasma membrane)

Halorhodopsin - Proton pump

v·d·e
Hydrolases: acid anhydride hydrolases (EC 3.6)
3.6.1

Pyrophosphatase (Inorganic, Thiamine) - Apyrase - Thiamine triphosphatase

3.6.3-4

ATPase

3.6.5

GTPase


v·d·e
Acid anhydride hydrolases: ATPases (EC 3.6.3-3.6.4)
3.6.3

Cu++ (Menkes, Wilson) - Ca+ (SERCA, Plasma membrane) - Na+/K+ - H+/K+ - ATP synthase - H+ (F-type) - H+ (V-type)

3.6.4

Dynein - Kinesin - Myosin

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