An enzyme that catalyzes the hydrolysis of ATP to ADP, releasing energy that is used in the cell; adenosine triphosphatase.
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An enzyme that catalyzes the hydrolysis of ATP to ADP, releasing energy that is used in the cell; adenosine triphosphatase.
Adenosine triphosphatase; an enzyme that catalyzes the hydrolysis of ATP.
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
Some such enzymes are integral membrane proteins (anchored within biological membranes), and move solutes across the membrane. (These are called transmembrane ATPases).
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
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.
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.
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.
| Membrane transport protein: ion pumps | |
|---|---|
| Symporter, Cotransporter | Na+/K+/2Cl- - Na/Pi3 - Na+/Cl- - Na/glucose - Na+/I- |
| Antiporter (exchanger) | Na+/H+ - Na+/Ca2+ (Na+/(Ca2+-K+)) - Cl-/HCO3- (Band 3) |
| ATPase | Cu++ - Ca+ (SERCA-ATP2A2, [[Plasma membrane Ca2+ ATPase|Plasma membrane]]) - [[Na+/K+-ATPase|Na+/K+]] - H+/K+ - ATP synthase - H+ (F-type) - H+ (V-type) |
| Other | Uniporter - Halorhodopsin - Proton pump |
| 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 |
| Acid anhydride hydrolases: ATPases (EC 3.6.3-3.6.4) | |
|---|---|
| 3.6.3 | Cu++ (Menkes, Wilson) - Ca+ (SERCA, [[Plasma membrane Ca2+ ATPase|Plasma membrane]]) - [[Na+/K+-ATPase|Na+/K+]] - H+/K+ - ATP synthase - H+ (F-type) - H+ (V-type) |
| 3.6.4 | Dynein - Kinesin - Myosin |
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