Transmembrane ATPase: Difference between revisions
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#REDIRECT [[ATPase]] |
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'''Transmembrane ATPases''' are [[integral membrane protein]]s that use energy from the [[hydrolysis]] of [[adenosine triphosphate]] (ATP) to transport [[ion]]s and other solutes between the solutions on either side of a [[biological membrane]] and against a solute's natural direction of flow. |
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Transmembrane ATPases import many of the metabolites necessary for [[biological cell|cell]] [[metabolism]] and export toxins, waste 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]]. |
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Besides exchangers, other categories of transmembrane ATPase include cotransporters 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, while others do not. These are called "electrogenic" and "nonelectrogenic" transporters, respectively. |
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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; 3 Na<sup>+</sup> ions inward and 2 K<sup>+</sup> ions outward per ATP hydrolyzed, in the Na<sup>+</sup>/K<sup>+</sup> exchanger. |
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Transmembrane ATPases harness the chemical potential energy of ATP, because they perform [[work]]: They transport solutes in a direction opposite to their [[thermodynamic|thermodynamically]] preferred direction of movement— from the side of the membrane where they are in low concentration to the side where they are in high concentration. This process is called [[active transport]]. |
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The ATP synthetase (or ATP synthase) of [[mitochondria]] and [[chloroplast]]s 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). ATP synthetase can also function in reverse; that is, use energy released by ATP hydrolysis to pump protons against their thermodynamic gradient. |
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Latest revision as of 05:13, 29 August 2004
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