Transmembrane ATPases are membrane-bound enzyme complexes/ion transporters that use ATP hydrolysis to drive the transport of protons across a membrane. Some transmembrane ATPases also work in reverse harnessing 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. There are several different types of transmembrane ATPases which can differ in function (ATP hydrolysis and/or synthesis) structure (e.g. F- V- and A-ATPases which contain rotary motors) and in the type of ions they transport . The different types include:
- 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).
- V-ATPases (V1V0-ATPases) which are primarily found in eukaryotic vacuoles and catalyse ATP hydrolysis to transport solutes and lower pH in organelles.
- 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).
- 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.
- E-ATPases which are cell-surface enzymes that hydrolyse a range of NTPs including extracellular ATP.
P-ATPases (also known as E1-E2 ATPases) (
) are found in bacteria and in a number of eukaryotic plasma membranes and organelles
. 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 which transport specific types of ion: H+
. P-ATPases can be composed of one or two polypeptides and can usually assume two main conformations called E1 and E2. This entry represents the alpha subunit found in the P-type cation exchange ATPases located in the plasma membranes of animal cells. These P-ATPases include both H+
) and Na+
) which belong to the IIC subfamily of ATPases
. These ATPases catalyse the hydrolysis of ATP coupled with the exchange of cations pumping one cation out of the cell (H+
) in exchange for K+
. These ATPases contain an alpha subunit that is the catalytic component and a regulatory beta subunit (
) that stabilises the alpha/beta assembly
. Different alpha and beta isoforms exist permitting greater regulatory control.An example of a H+
-ATPase is the gastric pump responsible for acid secretion in the stomach transporting protons from the cytoplasm of parietal cells to create a large pH gradient in exchange for the internalisation of potassium ions using ATP hydrolysis to drive the pump