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 ...

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 sign ...

involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

in opposite directions, one into the cell and one out of the cell. Na⁺/H⁺ antiporters have been reviewed. In secondary active transport, 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 ...

, allowing a different species to move against its own electrochemical gradient. This movement is in contrast to

primary 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 cellu ...

, 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) ...

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 an ...

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. Bacter ...

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 '' Esc ...

. 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 in ...

. 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. ...

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 m ...

References

External links

* * Integral membrane proteins Transport phenomena {{membrane-protein-stub

Role in Homeostatic Mechanisms

See also

References

External links