<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>A-ATPases (or A1A0-ATPase) (<db_xref db="EC" dbkey="3.6.3.14"/>) are found exclusively in Archaea and display a close resemblance in structure and subunit composition with V-ATPases, although their function in both ATP synthesis and ATP hydrolysis is closer to that of F-ATPases [<cite idref="PUB00020617"/>]. A-ATPases are composed of two linked complexes: the A1 complex consisting of seven subunits contains the catalytic core that synthesizes/hydrolyses ATP, while the A0 complex consisting of at least two subunits forms the membrane-spanning pore [<cite idref="PUB00002959"/>]. The rotary motor in A-ATPases is composed of only two subunits, the stator subunit I and the rotor subunit C [<cite idref="PUB00020618"/>]. A-ATPases may have arisen as an adaptation to the different cellular needs and the more extreme environmental conditions faced by Archaeal species.</p><p>This entry represents the subunit C of the A1 complex.</p> ATPase, A1 complex, subunit C