The electrochemical proton gradient across membranes and the acidic lumenal pH play vital bioenergetic or physiological roles in organelles, cells and tissues of animals and plants. They are required for ATP synthesis, solute transport, protein processing, exocytosis, endocytosis, etc. Proton-pumping ATPases are the major players in the transport of protons across membranes. The three classes of the ATPase family are the P-ATPase, F-ATPase and V-ATPase, the nomenclature being based on acyl phosphate intermediates, factors of oxidative phosphorylation and a pump found initially in vacuoles, respectively. F-ATPase and V-ATPase are similar in subunit structure and mechanism. However, F-ATPase is a ubiquitous ATP synthase in mitochondria, chloroplasts, and bacterial membranes, whereas V-ATPase is a proton pump in diverse endomembrane organelles such as lysosomes and endosomes. 


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