<p>ATPases (or ATP synthases) are membrane-bound enzyme complexes/ion transporters that combine ATP synthesis and/or hydrolysis with the transport of protons across a membrane. ATPases can harness the energy from a proton gradient, using the flux of ions across the membrane via the ATPase proton channel to drive the synthesis of ATP. Some ATPases work in reverse, using the energy from the hydrolysis of ATP to create a proton gradient. There are different types of ATPases, which can differ in function (ATP synthesis and/or hydrolysis), structure (e.g., F-, V- and A-ATPases, which contain rotary motors) and in the type of ions they transport [<cite idref="PUB00020603"/>, <cite idref="PUB00020604"/>]. The different types include:</p><p> <ul><li>F-ATPases (F1F0-ATPases), which are found in mitochondria, chloroplasts and bacterial plasma membranes where they are the prime producers of ATP, using the proton gradient generated by oxidative phosphorylation (mitochondria) or photosynthesis (chloroplasts).</li><li>V-ATPases (V1V0-ATPases), which are primarily found in eukaryotic vacuoles and catalyse ATP hydrolysis to transport solutes and lower pH in organelles.</li><li>A-ATPases (A1A0-ATPases), which are found in Archaea and function like F-ATPases (though with respect to their structure and some inhibitor responses, A-ATPases are more closely related to the V-ATPases).</li><li>P-ATPases (E1E2-ATPases), which are found in bacteria and in eukaryotic plasma membranes and organelles, and function to transport a variety of different ions across membranes.</li><li>E-ATPases, which are cell-surface enzymes that hydrolyse a range of NTPs, including extracellular ATP.</li> </ul> </p><p>P-ATPases (sometime known as E1-E2 ATPases) (<db_xref db="EC" dbkey="3.6.3.-"/>) are found in bacteria and in a number of eukaryotic plasma membranes and organelles [<cite idref="PUB00009616"/>]. P-ATPases function to transport a variety of different compounds, including ions and phospholipids, across a membrane using ATP hydrolysis for energy. There are many different classes of P-ATPases, each of which transports a specific type of ion: H<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Mg<sup>2+</sup>, Ca<sup>2+</sup>, Ag<sup>+</sup> and Ag<sup>2+</sup>, Zn<sup>2+</sup>, Co<sup>2+</sup>, Pb<sup>2+</sup>, Ni<sup>2+</sup>, Cd<sup>2+</sup>, Cu<sup>+</sup> and Cu<sup>2+</sup>. P-ATPases can be composed of one or two polypeptides, and can usually assume two main conformations called E1 and E2.</p><p>H+-Transporting ATPases (proton pumps) are the main ion pumps in the plasma membrane and play a central role [<cite idref="PUB00004574"/>] in the physiology and bioenergetics of plant cells. They are the primary active transporters of the plasma membrane and are responsible for generating the membrane potential that drives translocation of cations, amino-acids, sugars, and hormones, whilst also contributing to the maintenance of intracellular and extracellular pH and cell turgor [<cite idref="PUB00002571"/>]. Proton pumps are members of the P-type (or E1-E2-type) cation-transporting ATPase superfamily, which has evolved from a common ancestral gene [<cite idref="PUB00003431"/>]. The sequences are believed to contain 8-10 transmembrane helices, some of which are well conserved throughout the superfamily. They may thus all operate via a similar mechanism, with an aspartylphosphoryl enzyme intermediate [<cite idref="PUB00002426"/>] being formed during the catalytic cycle.</p><p>More information about this protein can be found at Protein of the Month: ATP Synthases [<cite idref="PUB00020719"/>].</p>