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In the field of enzymology, a proton ATPase, or H⁺-ATPase, is an enzyme that catalyzes the following chemical reaction:

ATP + H
₂O + H⁺
_in

\rightleftharpoons

ADP + phosphate + H⁺
_out

The 3 substrates of this enzyme are ATP, H
₂O, and H⁺
, whereas its 3 products are ADP, phosphate, and H⁺
.

Proton ATPases are divided into three groups^[1] as outlined below:

P-type proton ATPase

P-type ATPases form a covalent phosphorylated (hence the symbol ’P') intermediate as part of its reaction cycle. P-type ATPases undergo major conformational changes during the catalytic cycle. P-type ATPases are not evolutionary related to V- and F-type ATPases.^[1]

Plasma membrane H⁺-ATPase

P-type proton ATPase^[2]^[3]^[4]^[5] (or plasma membrane H⁺
-ATPase) is found in the plasma membranes of eubacteria, archaea, protozoa, fungi and plants. Here it serves as a functional equivalent to the Na⁺/K⁺ ATPase of animal cells; i.e. it energizes the plasma membrane by forming an electrochemical gradient of protons (Na⁺ in animal cells), that in turn drives secondary active transport processes across the membrane. The plasma membrane H⁺-ATPase is a P3A ATPase with a single polypeptide of 70-100 kDa.

Gastric H⁺/K⁺ ATPase

Animals have a gastric hydrogen potassium ATPase or H⁺/K⁺ ATPase that belongs to the P-type ATPase family and functions as an electroneutral proton pump. This pump is found in the plasma membrane of cells in the gastric mucosa and functions to acidify the stomach.^[6] This enzyme is a P2C ATPase, characterized by having a supporting beta-subunit, and is closely related to the Na⁺/K⁺ ATPase.

V-type proton ATPase

V-type proton ATPase^[7]^[8]^[9] (or V-ATPase) translocate protons into intracellular organelles other than mitochondria and chloroplasts, but in certain cell types they are also found in the plasma membrane. V-type ATPases acidify the lumen of the vacuole (hence the symbol 'V') of fungi and plants, and that of the lysosome in animal cells. Furthermore, they are found in endosomes, clathrin coated vesicles, hormone storage granules, secretory granules, Golgi vesicles and in the plasma membrane of a variety of animal cells. Like F-type ATPases, V-type ATPases are composed of multiple subunits and carry out rotary catalysis.^[10] The reaction cycle involves tight binding of ATP but proceeds without formation of a covalent phosphorylated intermediate. V-type ATPases are evolutionary related to F-type ATPases.^[11]

F-type proton ATPase

F-type proton ATPase^[12]^[13] (or F-ATPase) typically operates as an ATP synthase that dissipates a proton gradient rather than generating one; i.e. protons flow in the reverse direction compared to V-type ATPases. In eubacteria, F-type ATPases are found in plasma membranes. In eukaryotes, they are found in the mitochondrial inner membranes and in chloroplast thylakoid membranes. Like V-type ATPases, F-type ATPases are composed of multiple subunits and carry out rotary catalysis. The reaction cycle involves tight binding of ATP but proceeds without formation of a covalent phosphorylated intermediate. F-type ATPases are evolutionary related to V-type ATPases.^[11]

References

^ ^a ^b Pedersen PL, Carafoli E (1987). "Ion motive ATPases. I. Ubiquity, properties, and significance to cell function". Trends in Biochemical Sciences. 12: 146–50. doi:10.1016/0968-0004(87)90071-5.
^ Goffeau A, Slayman CW (December 1981). "The proton-translocating ATPase of the fungal plasma membrane". Biochimica et Biophysica Acta (BBA) - Reviews on Bioenergetics. 639 (3–4): 197–223. doi:10.1016/0304-4173(81)90010-0. PMID 6461354.
^ Morsomme P, Slayman CW, Goffeau A (November 2000). "Mutagenic study of the structure, function and biogenesis of the yeast plasma membrane H(+)-ATPase". Biochimica et Biophysica Acta (BBA) - Reviews on Biomembranes. 1469 (3): 133–57. doi:10.1016/S0304-4157(00)00015-0. PMID 11063881.
^ Palmgren MG (June 2001). "PLANT PLASMA MEMBRANE H+-ATPases: Powerhouses for Nutrient Uptake". Annual Review of Plant Physiology and Plant Molecular Biology. 52: 817–845. doi:10.1146/annurev.arplant.52.1.817. PMID 11337417.
^ Morth JP, Pedersen BP, Buch-Pedersen MJ, Andersen JP, Vilsen B, Palmgren MG, Nissen P (January 2011). "A structural overview of the plasma membrane Na+,K+-ATPase and H+-ATPase ion pumps". Nature Reviews. Molecular Cell Biology. 12 (1): 60–70. doi:10.1038/nrm3031. PMID 21179061.
^ Sachs G, Shin JM, Briving C, Wallmark B, Hersey S (1995). "The pharmacology of the gastric acid pump: the H+,K+ ATPase". Annu Rev Pharmacol Toxicol. 35: 277–305. doi:10.1146/annurev.pa.35.040195.001425. PMID 7598495.
^ Beyenbach KW, Wieczorek H (February 2006). "The V-type H+ ATPase: molecular structure and function, physiological roles and regulation". The Journal of Experimental Biology. 209 (Pt 4): 577–89. doi:10.1242/jeb.02014. PMID 16449553.
^ Nelson N (November 1992). "The vacuolar H(+)-ATPase--one of the most fundamental ion pumps in nature". The Journal of Experimental Biology. 172: 19–27. PMID 1337091.
^ Marshansky V, Rubinstein JL, Grüber G (June 2014). "Eukaryotic V-ATPase: novel structural findings and functional insights". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1837 (6): 857–79. doi:10.1016/j.bbabio.2014.01.018. PMID 24508215.
^ Stewart AG, Laming EM, Sobti M, Stock D (April 2014). "Rotary ATPases--dynamic molecular machines". Current Opinion in Structural Biology. 25: 40–8. doi:10.1016/j.sbi.2013.11.013. PMID 24878343.
^ ^a ^b Mulkidjanian AY, Makarova KS, Galperin MY, Koonin EV (November 2007). "Inventing the dynamo machine: the evolution of the F-type and V-type ATPases". Nature Reviews. Microbiology. 5 (11): 892–9. doi:10.1038/nrmicro1767. PMID 17938630.
^ Boyer PD (1997). "The ATP synthase--a splendid molecular machine". Annual Review of Biochemistry. 66: 717–49. doi:10.1146/annurev.biochem.66.1.717. PMID 9242922.
^ Junge W, Nelson N (2015). "ATP synthase". Annual Review of Biochemistry. 84: 631–57. doi:10.1146/annurev-biochem-060614-034124. PMID 25839341.