Editing Proton pump

{{Short description|Transport protein}}
{{About|biochemical proton pumps|generators of [[proton beam]]s|synchrotron|and|cyclotron}}

[[File:Structure_of_the_V-ATPase_proton_pump.jpg | thumb | right | A V-ATPase proton pump]]
A '''proton pump''' is an [[integral membrane protein]] pump that builds up a [[electrochemical gradient|proton gradient]] across a [[biological membrane]]. Proton pumps catalyze the following reaction:

:{{chem|H|+}}<sub>[on one side of a biological membrane]</sub> + energy  {{eqm}}  {{chem|H|+}}<sub>[on the other side of the membrane]</sub>

Mechanisms are based on energy-induced [[Protein conformation|conformational]] changes of the protein structure or on the [[Q cycle]].

During evolution, proton pumps have arisen independently on multiple occasions. Thus, not only throughout nature, but also within single cells, different proton pumps that are evolutionarily unrelated can be found. Proton pumps are divided into different major classes of pumps that use different sources of energy, exhibiting different polypeptide compositions and evolutionary origins.

==Function==
Transport of the positively charged proton is typically electrogenic, i.e.: it generates an electric field across the membrane also called the [[membrane potential]]. Proton transport becomes electrogenic if not neutralized electrically by transport of either a corresponding negative charge in the same direction or a corresponding positive charge in the opposite direction. An example of a proton pump that is not electrogenic, is the [[Hydrogen potassium ATPase|proton/potassium pump]] of the [[gastric mucosa]] which catalyzes a balanced exchange of protons and potassium ions.{{Citation needed|date=August 2023}}

The combined transmembrane gradient of protons and charges created by proton pumps is called an [[electrochemical gradient]]. An electrochemical gradient represents a store of energy ([[potential energy]]) that can be used to drive a multitude of biological processes such as [[ATP synthesis]], nutrient uptake and action potential formation.{{Citation needed|date=August 2023}}

In [[cell respiration]], the proton pump uses energy to transport protons from the [[matrix (biology)|matrix]] of the [[mitochondrion]] to the inter-membrane space.<ref>
{{cite book
|first1=Shinya
|last1= Yoshikawa
|first2=Atsuhiro
|last2=Shimada
|first3=Kyoko
|last3=Shinzawa-Itoh
|editor=Peter M.H. Kroneck and Martha E. Sosa Torres
|title=Sustaining Life on Planet Earth: Metalloenzymes Mastering Dioxygen and Other Chewy Gases
|series=Metal Ions in Life Sciences
|volume=15
|year=2015
|publisher=Springer
|chapter=Chapter 4, Section 4 ''Proton Pump Mechanism''
|pages=108–111
|doi=10.1007/978-3-319-12415-5_4
|pmid= 25707467
}}
</ref> It is an active pump that generates a proton [[gradient|concentration gradient]] across the inner mitochondrial membrane, because there are more protons outside the matrix than inside. The difference in [[pH]] and [[electric charge]] (ignoring differences in [[Buffering agent|buffer]] capacity) creates an [[electrochemical potential]] difference that works similar to that of a battery or energy storing unit for the cell.<ref>Campbell, N.A., 2008. Resource Acquisition and Transport in Vascular Plants. 8th ed., Biology. San Francisco: Pearson Benjamin Cummings.</ref>
The process could also be seen as analogous to cycling uphill or charging a battery for later use, as it produces [[potential energy]]. The proton pump does not create energy, but forms a gradient that stores energy for later use.<ref>{{cite journal | doi=10.1038/465428a | title=Piston drives a proton pump | year=2010 | last1=Ohnishi | first1=Tomoko | journal=Nature | volume=465 | issue=7297 | pages=428–429 | pmid=20505714 | s2cid=205055904 | doi-access=free }}</ref>

==Diversity==
The energy required for the proton pumping reaction may come from light (light energy; [[bacteriorhodopsin]]s), electron transfer (electrical energy; electron transport complexes [[NADH dehydrogenase (ubiquinone)|I]], [[Coenzyme Q – cytochrome c reductase|III]] and [[Cytochrome c oxidase|IV]]) or energy-rich metabolites (chemical energy) such as [[pyrophosphate]] (PPi; [[proton-pumping pyrophosphatase]]) or [[adenosine triphosphate]] (ATP; [[proton ATPase]]s).{{Citation needed|date=August 2023}}

==Electron-transport-driven proton pumps==
{{See also|Electron transport chain}}
===Electron transport complex I===
{{Main|NADH dehydrogenase (ubiquinone)}}

[[NADH dehydrogenase (ubiquinone)|Complex I]] (EC 1.6.5.3) (also referred to as [https://www.life.illinois.edu/crofts/bioph354/complex_i.html NADH:ubiquinone oxidoreductase] or, especially in the context of the human protein, [[NADH dehydrogenase]]) is a proton pump driven by electron transport. It belongs to the [[Respiratory complex I|H<sup>+</sup> or Na<sup>+</sup>-translocating NADH Dehydrogenase (NDH) Family]] (TC# 3.D.1), a member of the Na<sup>+</sup> transporting [[Mrp superfamily]]. It [[wikt:catalyze|catalyzes]] the transfer of electrons from NADH to [[Coenzyme Q10|coenzyme Q10 (CoQ10]]) and, in [[eukaryote]]s, it is located in the [[inner mitochondrial membrane]]. This enzyme helps to establish a transmembrane difference of proton electrochemical potential that the [[ATP synthase]] then uses to [https://www.britannica.com/science/metabolism/ATP-synthesis-in-mitochondria synthesize ATP].{{Citation needed|date=August 2023}}

===Electron transport complex III===
{{Main|Coenzyme Q – cytochrome c reductase}}

[[Coenzyme Q – cytochrome c reductase|Complex III]] (EC 1.10.2.2) (also referred to as [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC372766/ cytochrome b<sub>c</sub>1] or the [[Coenzyme Q – cytochrome c reductase|coenzyme Q : cytochrome c – oxidoreductase]]) is a proton pump driven by electron transport. Complex III is a multi-subunit [[transmembrane protein]] encoded by both the [[Cytochrome b|mitochondrial (cytochrome b)]] and the [[Nuclear DNA|nuclear genomes]] (all other subunits). Complex III is present in the inner mitochondrial membrane of all aerobic eukaryotes and the inner membranes of most eubacteria. This enzyme helps to establish a transmembrane difference of proton electrochemical potential that the ATP synthase of mitochondria then uses to synthesize ATP.{{Citation needed|date=August 2023}}

===The cytochrome b<sub>6</sub>f complex===
{{Main|Cytochrome b6f complex}}

The [[Cytochrome b6f complex|cytochrome b<sub>6</sub>f complex]] (EC 1.10.99.1) (also called plastoquinol—plastocyanin reductase) is an enzyme related to Complex III but found in the [[Thylakoid|thylakoid membrane]] in chloroplasts of plants, [[cyanobacteria]], and green algae. This proton pump is driven by electron transport and catalyzes the transfer of electrons from [[Plastoquinone|plastoquinol]] to [[plastocyanin]]. The reaction is analogous to the reaction catalyzed by Complex III (cytochrome bc1) of the [[mitochondrial electron transport chain]]. This enzyme helps to establish a transmembrane difference of proton electrochemical potential that the ATP synthase of chloroplasts then uses to synthesize ATP.{{Citation needed|date=August 2023}}

===Electron transport complex IV===
{{Main|Cytochrome c oxidase}}

[[Cytochrome c oxidase|Complex IV]] (EC 1.9.3.1) (also referred to as cytochrome c oxidase), is a proton pump driven by electron transport.  This enzyme is a large transmembrane protein complex found in bacteria and inner mitochondrial membrane of eukaryotes. It receives an electron from each of four [[Cytochrome c|cytochrome c molecules]], and transfers them to one oxygen molecule, converting molecular oxygen to two molecules of water. In the process, it binds four protons from the inner aqueous phase to make water and in addition [[wikt:translocate|translocates]] four protons across the membrane. This enzyme helps to establish a transmembrane difference of proton electrochemical potential that the ATP synthase of mitochondria then uses to synthesize ATP.{{Citation needed|date=August 2023}}

==ATP-driven proton pumps==
{{Main|Proton ATPase}}

[[Proton ATPase|Proton pumps driven by adenosine triphosphate (ATP)]] (also referred to as proton ATPases or {{chem|H|+}}-ATPases) are proton pumps driven by the hydrolysis of [[adenosine triphosphate]] (ATP). Three classes of proton ATPases are found in nature. In a single cell (for example those of fungi and plants), representatives from all three groups of proton ATPases may be present.{{Citation needed|date=August 2023}}

===P-type proton ATPase===
{{Main|Plasma membrane H+-ATPase}}

The [[Plasma membrane H+-ATPase|plasma membrane {{chem|H|+}}-ATPase]] is a single subunit P-type ATPase found in the plasma membrane of [[plants]], [[fungi]], [[protists]] and many [[prokaryotes]].{{Citation needed|date=August 2023}}

The [[Plasma membrane H+-ATPase|plasma membrane {{chem|H|+}}-ATPase]] creates the [[electrochemical gradients]] in the [[plasma membrane]] of [[plants]], [[fungi]], [[protists]], and many [[prokaryotes]]. Here, proton gradients are used to drive [[Secondary active transport|secondary transport]] processes. As such, it is essential for the uptake of most [[metabolites]], and also for responses to the environment (e.g., movement of leaves in plants).{{Citation needed|date=August 2023}}

Humans (and probably other mammals) have a gastric [[hydrogen potassium ATPase]] or H<sup>+</sup>/K<sup>+</sup> ATPase that also belongs to the [[P-type ATPase|P-type ATPase family]]. This enzyme functions as the proton pump of the [[stomach]], primarily responsible for the acidification of the stomach contents (see [[gastric acid]]).{{Citation needed|date=August 2023}}

===V-type proton ATPase===
{{Main|V-ATPase}}

The [[V-ATPase|V-type proton ATPase]] is a multi-subunit enzyme of the [[V-ATPase|V-type]]. It is found in various different membranes where it serves to acidify [[Organelle|intracellular organelles]] or the [[Cell membrane|cell exterior]].{{Citation needed|date=August 2023}}

===F-type proton ATPase===
{{Main|F-ATPase}}

The [[ATP synthase|F-type proton ATPase]] is a multi-subunit enzyme of the [[F-ATPase|F-type]]  (also referred to as [[ATP synthase]] or F<sub>O</sub>F<sub>1</sub> ATPase). It is found in the mitochondrial inner membrane where it functions as a proton transport-driven [[ATP synthase]].

In [[mitochondria]], [[electrochemistry|reducing equivalents]] provided by [[electron transfer chain|electron transfer]] or [[photosynthesis]] power this translocation of protons. For example, the translocation of protons by [[cytochrome c oxidase]] is powered by reducing equivalents provided by reduced [[cytochrome c]]. ATP itself powers this transport in the [[plasma membrane]] proton ATPase and in the [[transmembrane ATPase|ATPase]] proton pumps of other cellular membranes.{{Citation needed|date=August 2023}}

The F<sub>o</sub>F<sub>1</sub> [[ATP synthase]] of mitochondria, in contrast, usually conduct protons from high to low concentration across the membrane while drawing energy from this flow to synthesize ATP. Protons translocate across the inner mitochondrial membrane via proton wire. This series of conformational changes, channeled through the a and b subunits of the F<sub>O</sub> particle, drives a series of conformational changes in the stalk connecting the F<sub>O</sub> to the F<sub>1</sub> subunit. This process effectively couples the translocation of protons to the mechanical motion between the Loose, Tight, and Open states of F<sub>1</sub> necessary to phosphorylate ADP.{{Citation needed|date=August 2023}}

In [[bacteria]] and ATP-producing organelles other than mitochondria, [[electrochemistry|reducing equivalents]] provided by [[electron transfer chain|electron transfer]] or [[photosynthesis]] power the translocation of protons.{{Citation needed|date=August 2023}}

CF<sub>1</sub> ATP [[ligase]] of [[chloroplast]]s correspond to the human F<sub>O</sub>F<sub>1</sub> ATP synthase in plants.{{Citation needed|date=August 2023}}

==Pyrophosphate driven proton pumps==
{{Main|H+, Na+-translocating pyrophosphatase family}}

[[H+, Na+-translocating pyrophosphatase family|Proton pumping pyrophosphatase]] (also referred to as H{{chem|H|+}}-PPase or vacuolar-type inorganic pyrophosphatases (V-PPase; V is for vacuolar)) is a proton pump driven by the hydrolysis of inorganic pyrophosphate (PPi). In plants, H{{chem|H|+}}-PPase is localized to the vacuolar membrane (the tonoplast). This membrane of plants contains two different proton pumps for acidifying the interior of the [[vacuole]], the V-PPase and the V-ATPase.{{Citation needed|date=August 2023}}

==Light driven proton pumps==
{{Main|Bacteriorhodopsin}}

[[Bacteriorhodopsin]] is a light-driven proton pump used by [[Archaea]], most notably in [[Haloarchaea]]. Light is absorbed by a [[retinal]] pigment covalently linked to the protein, that results in a conformational change of the molecule that is transmitted to the pump protein associated with proton pumping.{{Citation needed|date=August 2023}}

==See also==
* [[Active transport]]
* [[Chemiosmosis]]
* [[Cytochrome]]
* [[Protonophore]]
* [[Proton-pump inhibitor]]
* [[Uncoupler]]
* [[2,4-Dinitrophenol]]
* [[V-ATPase]]

==References==
{{reflist}}

==External links==
* [https://web.archive.org/web/20090414122958/http://www.1lec.com/Biochemistry/Proton%20Pump/index.html Proton pump animation]
* {{MeshName|Proton+Pumps}}

{{Ion pumps}}
{{Proton pumps}}

{{DEFAULTSORT:Proton pump}}
[[Category:Transport proteins]]
[[Category:Proton]]