Proton pump
Encyclopedia
A proton pump is an integral membrane protein
that is capable of moving proton
s across a cell membrane
, mitochondrion
, or other organelle
. Mechanisms are based on conformational changes of the protein structure or on the Q cycle
.
of the mitochondrion
into the space between the inner and outer mitochondrial membranes. This action creates a concentration gradient
across the inner mitochondrial membrane, as there are more protons outside the matrix than in. This difference in pH
and electric charge
(ignoring differences in buffer
capacity) establishes an electrochemical potential that acts as a kind of battery or reservoir of stored energy for the cell, that functions in a similar way to a dam in a river. The process could also be seen as analogous to cycling uphill or charging a battery for later use, as it produces potential energy
. It is important to remember that the proton pump does not create energy, but instead creates a gradient that stores energy that is later used to drive cellular processes.
travel along the matrix, like freight boats, navigating up and down the river.
Others such as NADH-Q reductase
, act like ferryboats and cross the matrix. Enzymes that cross the matrix may have a secondary role as proton pumps because they can deliver protons to the inner membrane.
provided by 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
. In the plasma membrane proton ATPase and in the ATPase proton pumps of other cellular membranes, ATP itself powers this transport.
The FoF1 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. To allow the passage of protons a proton channel
temporarily opens in the inner membrane.
The gastric hydrogen potassium ATPase
or H+/K+ ATPase is the proton pump of the stomach
, which is responsible primarily for the acidification of the stomach contents (see gastric acid
).
and other ATP-producing organelles than mitochondria, reducing equivalents
provided by electron transfer or photosynthesis
power the translocation of protons.
CF1 ATP ligase
of chloroplast
s correspond to the human FoF1 ATP synthase in plants.
Bacteriorhodopsin
is a photosynthetic
pigment
used by archaea
, the most notable one being halobacteria
.
Integral membrane protein
An integral membrane protein is a protein molecule that is permanently attached to the biological membrane. Proteins that cross the membrane are surrounded by "annular" lipids, which are defined as lipids that are in direct contact with a membrane protein...
that is capable of moving proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s across a cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
, mitochondrion
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
, or other organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
. Mechanisms are based on conformational changes of the protein structure or on the Q cycle
Q cycle
- History :The Q cycle describes a series of reactions first proposed by Peter Mitchell that describe how the sequential oxidation and reduction of the lipophilic electron carrier, ubiquinol-ubiquinone , can result in the net pumping of protons across a lipid bilayer...
.
Function
In cell respiration, the pump actively transports protons from the matrixMatrix (biology)
In biology, matrix is the material between animal or plant cells, in which more specialized structures are embedded, and a specific part of the mitochondrion that is the site of oxidation of organic molecules. The internal structure of connective tissues is an extracellular matrix...
of the mitochondrion
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
into the space between the inner and outer mitochondrial membranes. This action creates a concentration gradient
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
across the inner mitochondrial membrane, as there are more protons outside the matrix than in. This difference in pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
and electric charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
(ignoring differences in buffer
Buffering agent
A buffering agent is a weak acid or base used to maintain the acidity of a solution at a chosen value. The function of a buffering agent is to prevent a rapid change in pH when acids or bases are added to the solution. Buffering agents have variable properties—some are more soluble than others;...
capacity) establishes an electrochemical potential that acts as a kind of battery or reservoir of stored energy for the cell, that functions in a similar way to a dam in a river. The process could also be seen as analogous to cycling uphill or charging a battery for later use, as it produces potential energy
Potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
. It is important to remember that the proton pump does not create energy, but instead creates a gradient that stores energy that is later used to drive cellular processes.
Mobility
Some of the enzymes involved in the electron transport chainElectron transport chain
An electron transport chain couples electron transfer between an electron donor and an electron acceptor with the transfer of H+ ions across a membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate...
travel along the matrix, like freight boats, navigating up and down the river.
Others such as NADH-Q reductase
Reductase
-Examples:* 5-alpha reductase* Dihydrofolate reductase* HMG-CoA reductase* Methemoglobin reductase* Ribonucleotide reductase* Thioredoxin reductase* E. coli nitroreductase* Methylenetetrahydrofolate reductase...
, act like ferryboats and cross the matrix. Enzymes that cross the matrix may have a secondary role as proton pumps because they can deliver protons to the inner membrane.
In eukaryotes
In mitochondria, reducing equivalentsElectrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
provided by electron transfer or photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
power this translocation of protons. For example, the translocation of protons by cytochrome c oxidase
Cytochrome c oxidase
The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria and the mitochondrion.It is the last enzyme in the respiratory electron transport chain of mitochondria located in the mitochondrial membrane...
is powered by reducing equivalents provided by reduced cytochrome c
Cytochrome c
The Cytochrome complex, or cyt c is a small heme protein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins. Cytochrome c is a highly soluble protein, unlike other cytochromes, with a solubility of about 100 g/L and is an...
. In the plasma membrane proton ATPase and in the ATPase proton pumps of other cellular membranes, ATP itself powers this transport.
The FoF1 ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
of mitochondria, in contrast, usually conduct protons from high to low concentration across the membrane while drawing energy from this flow to synthesize ATP. To allow the passage of protons a proton channel
Ion channel
Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...
temporarily opens in the inner membrane.
The gastric hydrogen potassium ATPase
Hydrogen potassium ATPase
Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
or H+/K+ ATPase is the proton pump of the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, which is responsible primarily for the acidification of the stomach contents (see gastric acid
Gastric acid
Gastric acid is a digestive fluid, formed in the stomach. It has a pH of 1 to 2 and is composed of hydrochloric acid , and large quantities of potassium chloride and sodium chloride...
).
In prokaryotes
In bacteriaBacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and other ATP-producing organelles than mitochondria, reducing equivalents
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
provided by electron transfer or photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
power the translocation of protons.
CF1 ATP ligase
Ligase
In biochemistry, ligase is an enzyme that can catalyse the joining of two large molecules by forming a new chemical bond, usually with accompanying hydrolysis of a small chemical group dependent to one of the larger molecules...
of chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
s correspond to the human FoF1 ATP synthase in plants.
Bacteriorhodopsin
Bacteriorhodopsin
Bacteriorhodopsin is a protein used by Archaea, the most notable one being Halobacteria. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell...
is a photosynthetic
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
used by archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
, the most notable one being halobacteria
Halobacteria
In taxonomy, the Halobacteria are a class of the Euryarchaeota, found in water saturated or nearly saturated with salt. They are also called halophiles, though this name is also used for other organisms which live in somewhat less concentrated salt water...
.
See also
- transmembrane ATPase
- active transportActive transportActive transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
- cytochromeCytochromeCytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....
- mitochondrionMitochondrionIn cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
- chloroplastChloroplastChloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
- electron transfer chain
- proton pump inhibitorProton pump inhibitorProton-pump inhibitors are a group of drugs whose main action is a pronounced and long-lasting reduction of gastric acid production. They are the most potent inhibitors of acid secretion available today. The group followed and has largely superseded another group of pharmaceuticals with similar...
- uncoupling proteinUncoupling proteinAn uncoupling protein is a mitochondrial inner membrane protein that can dissipate the proton gradient before it can be used to provide the energy for oxidative phosphorylation.There are five types known in mammals:* UCP1, also known as thermogenin* UCP2...
- protonophoreProtonophoreA protonophore, also known as a proton translocator, is an ionophore that allows protons to cross lipid bilayers. This would otherwise not occur as protons have positive charge and hydrophilic properties, making them unable to cross without a channel or transporter...
- 2,4-Dinitrophenol2,4-Dinitrophenol2,4-Dinitrophenol , C6H4N2O5, is a cellular metabolic poison. It uncouples oxidative phosphorylation by carrying protons across the mitochondrial membrane, leading to a rapid consumption of energy without generation of ATP....
- ATP synthaseATP synthaseright|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
- V-ATPaseV-ATPaseVacuolar-type H+-ATPase is a highly conserved evolutionarily ancient enzyme with remarkably diverse functions in eukaryotic organisms. V-ATPases acidify a wide array of intracellular organelles and pump protons across the plasma membranes of numerous cell types...
- proton ATPaseProton ATPaseIn the field of enzymology, the proton-ATPase is an enzyme that catalyzes the following chemical reaction:The 3 substrates of this enzyme are ATP, H2O, and H+, whereas its 3 products are ADP, phosphate, and H+....