Antiporter

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Comparison of transport proteins Porters.PNG
Comparison of transport proteins
Antiporter illustration Antiporter.jpg
Antiporter illustration

An antiporter (also called exchanger or counter-transporter) is a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions, one into the cell and one out of the cell. Na+/H+ antiporters have been reviewed. [1]

Contents

In secondary active transport, one species of solute moves along its electrochemical gradient, allowing a different species to move against its own electrochemical gradient. This movement is in contrast to primary active transport, in which all solutes are moved against their concentration gradients, fueled by ATP.

Transport may involve one or more of each type of solute. For example, the Na+/Ca2+ exchanger, found in the plasma membrane of many cells, moves three sodium ions in one direction, and one calcium ion in the other.

Role in Homeostatic Mechanisms

Na+/H+ Antiporters

Antiporters, such as Na+/H+ antiporter protein, allows ions H+ and Na+ to travel across a membrane in order to change a concentration gradient. [2] When pH within a cell is higher or lower than the optimal range it can be detrimental, therefore, the Na+/H+ antiporter detects the pH level out of range and is activated to transport ions as a homeostatic mechanism to bring the pH level back to optimal range. [3]

There are differences among the types of Na+/H+ antiporter families present in eukaryotes and prokaryotes. Prokaryotic organisms contain antiporter families such as NhaA, NhaB, NhaC, NhaD, NhaP, along with NapA. [2] The most prominent functions, including pH regulation, are completed by Na+/H+ antiporter family NhaA in prokaryotes like Escherichia coli. [2]

Plants are sensitive to high amounts of salt, which can halt certain necessary functions of the eukaryotic organism, including photosynthesis. [2] For the organisms to maintain homeostasis and carry out crucial functions, Na+/H+ antiporters are used to rid the cytoplasm of excess sodium by pumping Na+ out of the cell. [2] These antiporters can also close their channel to stop sodium from entering the cell, along with allowing excess sodium within the cell to enter into a vacuole. [2]

See also

Related Research Articles

In cellular biology, active transport is the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellular energy to achieve this movement. There are two types of active transport: primary active transport that uses adenosine triphosphate (ATP), and secondary active transport that uses an electrochemical gradient. Active transport does not follow Fick's first law and Second law of thermodynamics

ATPase dephosphorylation enzyme

ATPases (EC 3.6.1.3, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, SV40 T-antigen, adenosine 5'-triphosphatase, ATP hydrolase, complex V (mitochondrial electron transport), (Ca2+ + Mg2+)-ATPase, HCO3-ATPase, adenosine triphosphatase) are a class of enzymes that catalyze the decomposition of ATP into ADP and a free phosphate ion or the inverse reaction. This dephosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life.

Cotransporter

Cotransporters are a subcategory of membrane transport proteins (transporters) that couple the favorable movement of one molecule with its concentration gradient and unfavorable movement of another molecule against its concentration gradient. They enable cotransport and include antiporters and symporters. In general, cotransporters consist of two out of the three classes of integral membrane proteins known as transporters that move molecules and ions across biomembranes. Uniporters are also transporters but move only one type of molecule down its concentration gradient and are not classified as cotransporters.

Electrochemical gradient

An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the chemical gradient, or difference in solute concentration across a membrane, and the electrical gradient, or difference in charge across a membrane. When there are unequal concentrations of an ion across a permeable membrane, the ion will move across the membrane from the area of higher concentration to the area of lower concentration through simple diffusion. Ions also carry an electric charge that forms an electric potential across a membrane. If there is an unequal distribution of charges across the membrane, then the difference in electric potential generates a force that drives ion diffusion until the charges are balanced on both sides of the membrane.

Ion transporter

In biology, a transporter is a transmembrane protein that moves ions across a biological membrane to accomplish many different biological functions including, cellular communication, maintaining homeostasis, energy production, etc. There are different types of transporters including, pumps, uniporters, antiporters, and symporters. Active transporters or ion pumps are transporters that convert energy from various sources—including adenosine triphosphate (ATP), sunlight, and other redox reactions—to potential energy by pumping an ion up its concentration gradient. This potential energy could then be used by secondary transporters, including ion carriers and ion channels, to drive vital cellular processes, such as ATP synthesis.

Oxaloacetate decarboxylase

Oxaloacetate decarboxylase is a carboxy-lyase involved in the conversion of oxaloacetate into pyruvate.

Cell physiology is the biological study of the activities that take place in a cell to keep it alive. The term physiology refers to normal functions in a living organism. Animal cells, plant cells and microorganism cells show similarities in their functions even though they vary in structure.

Sodium–hydrogen antiporter

The sodium–hydrogen antiporter or sodium–proton exchanger (Na+/H+ exchanger) is a membrane protein that transports Na+ into the cell, and H+ out of the cell (antiport).

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

Propionigenium modestum is a gram-negative, strictly anaerobic organism. It is rod-shaped and around 0.5-0.6 x 0.5-2.0μm in size. It is important in the elucidation of mechanism of ATP synthase.

SLC9B2

Solute carrier family 9, subfamily B, member 2 is a protein that in humans is encoded by the SLC9B2 gene.

The ion transporter (IT) superfamily is a superfamily of secondary carriers that transport charged substrates.

NhaA family

Na+/H+ antiporter A (NhaA) family (TC# 2.A.33) contains a number of bacterial sodium-proton antiporter (SPAP) proteins. These are integral membrane proteins that catalyse the exchange of H+ for Na+ in a manner that is highly pH dependent. Homologues have been sequenced from a number of bacteria and archaea. Prokaryotes possess multiple paralogues. A representative list of the proteins that belong to the NhaA family can be found in the Transporter Classification Database.

The NhaB family belongs to the ion transporter (IT) superfamily. A representative list of proteins belonging to the NhaB family can be found in the Transporter Classification Database.

The NhaC family belongs to the Ion Transporter (IT) Superfamily. A representative list of proteins belonging to the NhaC family can be found in the Transporter Classification Database.

The NhaD family belongs to the Ion Transporter (IT) Superfamily. A representative list of proteins belonging to the NhaD family can be found in the Transporter Classification Database.

The NhaE family belongs to the Ion Transporter (IT) Superfamily. A representative list of proteins belonging to the NhaE family can be found in the Transporter Classification Database.

The Monovalent Cation (K+ or Na+):Proton Antiporter-3 (CPA3) Family (TC# 2.A.63) is a member of the Na+ transporting Mrp superfamily. The CPA3 family consists of bacterial multicomponent K+:H+ and Na+:H+ antiporters. The best characterized systems are the PhaABCDEFG system of Sinorhizobium meliloti (TC# 2.A.63.1.1) that functions in pH adaptation and as a K+ efflux system, and the MnhABCDEFG system of Staphylococcus aureus (TC# 2.A.63.1.3) that functions as a Na+ efflux Na+:H+ antiporter.

The inorganic phosphate transporter (PiT) family is a group of carrier proteins derived from Gram-negative and Gram-positive bacteria, archaea, and eukaryotes.

The Na+-transporting Carboxylic Acid Decarboxylase (NaT-DC) Family (TC# 3.B.1) is a family of porters that belong to the CPA superfamily. Members of this family have been characterized in both Gram-positive and Gram-negative bacteria. A representative list of proteins belonging to the NaT-DC family can be found in the Transporter Classification Database.

References

  1. Padan, Etana; Landau, Meytal (2016). "Chapter 12. Sodium-Proton (Na+/H+) Antiporters: Properties and Roles in Health and Disease". In Astrid, Sigel; Helmut, Sigel; Roland K.O., Sigel (eds.). The Alkali Metal Ions: Their Role in Life. Metal Ions in Life Sciences. 16. Springer. pp. 391–458. doi:10.1007/978-3-319-21756-7_12. PMID   26860308.
  2. 1 2 3 4 5 6 Padan, Etana; Venturi, Miro; Gerchman, Yoram; Dover, Nir (2001-05-01). "Na+/H+ antiporters". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1505 (1): 144–157. doi: 10.1016/S0005-2728(00)00284-X . ISSN   0005-2728. PMID   11248196.
  3. Padan, Etana (2014-07-01). "Functional and structural dynamics of NhaA, a prototype for Na+ and H+ antiporters, which are responsible for Na+ and H+ homeostasis in cells". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1837 (7): 1047–1062. doi: 10.1016/j.bbabio.2013.12.007 . ISSN   0005-2728. PMID   24361841.