ATPase

Adenosinetriphosphatase
Identifiers
EC number	3.6.1.3
CAS number	Template:CAS
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Search PMC articles PubMed articles NCBI proteins

Adenosine triphosphate

Adenosine diphosphate

ATPases (EC 3.6.1.3, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, SV40 T-antigen, adenosine 5'-triphosphatase, ATP hydrolase, complex V (mitochondrial electron transport), (Ca²⁺ + Mg²⁺)-ATPase, HCO₃⁻-ATPase, adenosine triphosphatase) are a class of enzymes that catalyze the decomposition of ATP into 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, typically against their concentration gradient. These are called transmembrane ATPases.

Functions

Na⁺/K⁺ATPase

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) that maintains the cell membrane potential. And 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.

Mechanism

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.

Transmembrane ATP synthases

Main article: ATP synthase

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 electrochemical gradient.

Classification

There are different types of ATPases, which can differ in function (ATP synthesis and/or hydrolysis), structure (F-, V- and A-ATPases contain rotary motors) and in the type of ions they transport.

• F-ATPases (F1FO-ATPases) in mitochondria, chloroplasts and bacterial plasma membranes are the prime producers of ATP, using the proton gradient generated by oxidative phosphorylation (mitochondria) or photosynthesis (chloroplasts).
• V-ATPases (V1VO-ATPases) are primarily found in eukaryotic vacuoles, catalysing ATP hydrolysis to transport solutes and lower pH in organelles like proton pump of lysosome.
• A-ATPases (A1AO-ATPases) are found in Archaea and function like F-ATPases
• P-ATPases (E1E2-ATPases) are found in bacteria, fungi and in eukaryotic plasma membranes and organelles, and function to transport a variety of different ions across membranes.
• E-ATPases are cell-surface enzymes that hydrolyse a range of NTPs, including extracellular ATP.

P-ATPase

Main article: P-ATPase

P-ATPases (sometime known as E1-E2 ATPases) are found in bacteria and also in eukaryotic plasma membranes and organelles. Its name is due to short time attachment of inorganic phosphate at the aspartate residues at the time of activation. Function of P-ATPase is to transport a variety of different compounds, like ions and phospholipids, across a membrane using ATP hydrolysis for energy. There are many different classes of P-ATPases, which transports a specific type of ion. P-ATPases may be composed of one or two polypeptides, and can usually take two main conformations, E1 and E2.

Human genes

(See Human ATPase)

• Na⁺/K⁺ transporting: ATP1A1, ATP1A2, ATP1A3, ATP1A4, ATP1B1, ATP1B2, ATP1B3, ATP1B4
• Ca⁺⁺ transporting: ATP2A1, ATP2A2, ATP2A3, ATP2B1, ATP2B2, ATP2B3, ATP2B4, ATP2C1, ATP2C2
• Mg⁺⁺ transporting: ATP3
• H⁺/K⁺ exchanging: ATP4A
• H⁺ transporting, mitochondrial: ATP5A1, ATP5B, ATP5C1, ATP5C2, ATP5D, ATP5E, ATP5F1, ATP5G1, ATP5G2, ATP5G3, ATP5H, ATP5I, ATP5J, ATP5J2, ATP5L, ATP5L2, ATP5O, ATP5S
• H⁺ transporting, lysosomal: ATP6AP1, ATP6AP2, ATP6V1A, ATP6V1B1, ATP6V1B2, ATP6V1C1, ATP6V1C2, ATP6V1D, ATP6V1E1, ATP6V1E2, ATP6V1F, ATP6V1G1, ATP6V1G2, ATP6V1G3, ATP6V1H, ATP6V0A1, ATP6V0A2, ATP6V0A4, ATP6V0B, ATP6V0C, ATP6V0D1, ATP6V0D2, ATP6V0E
• Cu⁺⁺ transporting: ATP7A, ATP7B
• Class I, type 8: ATP8A1, ATP8B1, ATP8B2, ATP8B3, ATP8B4
• Class II, type 9: ATP9A, ATP9B
• Class V, type 10: ATP10A, ATP10B, ATP10D
• Class VI, type 11: ATP11A, ATP11B, ATP11C
• H⁺/K⁺ transporting, nongastric: ATP12A
• type 13: ATP13A1, ATP13A2, ATP13A3, ATP13A4, ATP13A5

See also

• ATP synthase
• ATP synthase alpha/beta subunits
• AAA proteins
• P-ATPase

External links

• "ATP synthase - a splendid molecular machine"
• ATPase at the US National Library of Medicine Medical Subject Headings (MeSH)
• UMich Orientation of Proteins in Membranes families/superfamily-5 - Proton or sodium translocating F- and V-type ATPases
• UMich Orientation of Proteins in Membranes families/superfamily-22 - Different conformations of P-type ATPase
• Electron microscopy structures of ATPases from the EM Data Bank(EMDB)