F-ATPase

F-ATPase, also known as F-Type ATPase, is a transmembrane protein found in bacterial plasma membranes, mitochondrial inner membranes and in chloroplast thylakoid membranes. It uses a proton gradient to drive ATP synthesis by allowing the passive flux of protons across the membrane down their electrochemical gradient and using the energy released by the transport reaction to synthesise ATP from ADP and inorganic phosphate. In some bacteria, sodium ions may be used instead.

F-ATPase consists of two domains:
 * the Fo domain which is integral in the membrane
 * the F1 which is peripheral (on the side of the membrane that the protons are moving into).

Both of these domains consist of assemblies of subunit polypeptides, and together they form a rotary motor. As the protons bind to the subunits of the F0 domains they cause parts of it to rotate. This rotation is propagated by a 'camshaft' to the F1 domain. ADP and Pi (inorganic phosphate) bind spontaneously to the three β subunits of the F1 domain, so that every time it goes through a 120° rotation ATP is released (rotational catalysis).

The Bovine Mitochondrial F1-ATPase Complexed with the Inhibitor Protein If1 is commonly cited in the relevant literature. Examples of its use may be found in many cellular fundamental metabolic activities such as acidosis and alkalosis and respiratory gas exchange. See also acidemia.

V-ATPase is structurally similar although it works in reverse, hydrolysing ATP to build the proton gradient.