An antiporter (also called exchanger or counter-transporter) is a
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 e ...
and
integral membrane protein
An integral, or intrinsic, membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All ''transmembrane proteins'' are IMPs, but not all IMPs are transmembrane proteins. IMPs comprise a signi ...
involved in
secondary active transport
In cellular biology, ''active transport'' is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellul ...
of two or more different molecules or ions across a
phospholipid membrane
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many viru ...
such as the
plasma membrane in opposite directions, one into the cell and one out of the cell.
Na+/H+ antiporters have been reviewed.
In
secondary active transport
In cellular biology, ''active transport'' is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellul ...
, one species of solute moves along its
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 th ...
, 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 gradient
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) o ...
s, 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.
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
In chemistry, pH (), historically denoting "potential of hydrogen" (or "power of hydrogen"), is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of ions) are me ...
out of range and is activated to transport
ions
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
as a
homeostatic
In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
mechanism to bring the pH level back to optimal range.
There are differences among the types of Na+/H+ antiporter families present in
eukaryotes
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
and
prokaryotes. Prokaryotic organisms contain antiporter families such as
NhaA,
NhaB,
NhaC,
NhaD, NhaP, along with NapA.
The most prominent functions, including pH regulation, are completed by Na+/H+ antiporter family NhaA in prokaryotes like
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
.
Plants are sensitive to high amounts of salt, which can halt certain necessary functions of the eukaryotic organism, including
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
.
For the organisms to maintain homeostasis and carry out crucial functions, Na+/H+ antiporters are used to rid the
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...
of excess sodium by pumping Na+ out of the cell.
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
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
.
See also
*
Uniporter
A uniporter is a membrane transport protein that transports a single species of substrate ( charged or uncharged) across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one ...
*
Symporter
*
Facilitated diffusion
Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembra ...
References
External links
*
*
Integral membrane proteins
Transport phenomena
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