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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/09/06 13:31:31」(JST)

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How it works

A symporter is an integral membrane protein that is involved in movement of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in the same direction, and is, therefore, a type of cotransporter. Typically, the ion(s) will move down the electrochemical gradient, allowing the other molecule(s) to move against the concentration gradient. The movement of the ion(s) across the membrane is facilitated diffusion, and is coupled with the active transport of the molecule(s). Although two or more types of molecule are transported, there may be several molecules transported of each type.

Examples

SGLT1 in the intestinal epithelium transports sodium ions (Na⁺) and glucose across luminal membrane of the epithelial cells so that it can be absorbed into the bloodstream. This is the basis of oral rehydration therapy. If this symporter did not exist, individual sodium channels and glucose uniporters would not be able to transfer glucose against the concentration gradient and into the bloodstream.

Na⁺/K⁺/2Cl^- symporter in the loop of Henle in the renal tubules of the kidney transports 4 molecules of 3 different types; a sodium ion (Na⁺), a potassium ion (K⁺) and two chloride ions (2Cl^-). Loop diuretics such as furosemide (Lasix) act on this protein.

In the roots of plants, the H+/K+ symporters are only one member of a group of several symporters/antiporters that specifically allow only one charged hydrogen ion (more commonly known as a proton) and one charged K+ ion. This group of carriers all contribute to modulate the chemiosmotic potential inside the cell. Initially H+ is pumped into the area outside the root by H+ ATPase. This change in both the pH and electrochemical potential gradient between the inside of the cell and the outside produces a proton motive force, as the protons will want to naturally flow back into the area of low concentration and with a voltage closer to zero from their current situation of being in an area of high concentration of positively charged protons.

The reasons for this are twofold. For one, substances in nature have a tendency to move from areas of high concentration to areas of low concentration, as is evident by dropping a drop of food coloring in a glass of water. It does not aggregate, but begins to move from the highly concentrated areas (the colored areas) to the areas of low concentration (clear areas). Second, large groups of predominantly positively charged or negatively charged particles will naturally repel each other. This is demonstrated by attempting to push the two positive poles or two negative poles of a magnet together. Depending on the strength of the magnet, the repulsion may be so strong that it is impossible to push the magnets together unless aided by machinery. Proton motive force does work on the system by bringing ions back towards the epidermis of the root or surface of a root hair along with the protons. From the surface of the soil/root interface, specific carriers, like H+/K+ symporters allow the specific ions to come into the cell and the out the plasmodesmata/symporters/anitporters of the side of the cell facing away from the soil so that the essential element can make its way up the plant to the area it is needed so that it may supply the plant with important nutrients that are vital to the plant's being able to reach maturity.

The H+/K+ symporter, also called a proton pump, is used to increase acidity of stomach acid. Proton pump inhibitors irreversibly inhibit this enzyme, and so are used as pharmaceuticals whose main action is a pronounced and long-lasting reduction of gastric acid production.

External links

Symporters at the US National Library of Medicine Medical Subject Headings (MeSH)

English Journal

Transportation and kinetic analysis of Mo(VI) ions through a MDLM system containing TNOA as carrier.

Donat R1, Durmaz Ö2, Cetişli H1.
Journal of hazardous materials.J Hazard Mater.2015 Aug 30;294:17-26. doi: 10.1016/j.jhazmat.2015.03.031. Epub 2015 Mar 18.
In this report, Mo(VI) ions are transported from an aqueous donor phase into an aqueous acceptor phase by a newly designed method called as multi dropped liquid membrane (MDLM) system prepared by dissolving TNOA as carrier in kerosene. During the extraction of Mo(VI) ions by the liquid membrane syst
PMID 25841083

Interface-mediated fabrication of bowl-like and deflated ballon-like hollow carbon nanospheres.

Zhang H1, Li X2.
Journal of colloid and interface science.J Colloid Interface Sci.2015 Aug 15;452:141-7. doi: 10.1016/j.jcis.2015.04.027. Epub 2015 Apr 22.
In our work, two kinds of hollow carbon nanospheres with controlled morphologies have been successfully prepared from low-cost and nontoxic glucose as the sole carbon precursor under neutral aqueous medium via a simple hydrothermal route. During the process, sodium dodecylbenzene sulfonate (SDBS) an
PMID 25935285

Applicability of Donnan equilibrium theory at nanochannel-reservoir interfaces.

Tian H1, Zhang L1, Wang M2.
Journal of colloid and interface science.J Colloid Interface Sci.2015 Aug 15;452:78-88. doi: 10.1016/j.jcis.2015.03.064. Epub 2015 Apr 18.
Understanding ionic transport in nanochannels has attracted broad attention from various areas in energy and environmental fields. In most pervious research, Donnan equilibrium has been applied widely to nanofluidic systems to obtain ionic concentration and electrical potential at channel-reservoir
PMID 25932967

Japanese Journal

X線結晶構造解析と分子動力学シミュレーションで紐解く膜輸送体の分子機構

石谷隆一郎,道喜慎太郎,加藤英明 [他]
生物物理 54(2), 85-90,113, 2014-04
NAID 40020062424

X線結晶構造解析と分子動力学シミュレーションで紐解く膜輸送体の分子機構

石谷隆一郎,道喜慎太郎,加藤英明,濡木理
生物物理 54(2), 085-090, 2014
Membrane transporters transport their substrates across the membrane, thereby contributing to the maintenance of the cellular environments. One of the largest superfamily of the membrane transporters …
NAID 130003391407

Uptake Kinetics of 2,4-Dichlorophenoxyacetate by Delftia acidovorans MC1 and Derivative Strains : Complex Characteristics in Response to pH and Growth Substrate

Muller Roland H.,Hoffmann Doreen
Bioscience, biotechnology, and biochemistry 70(7), 1642-1654, 2006-07-23
… The presence of carbonylcyanide <I>m</I>-chlorophenylhydrazone led to the subsequent strong inhibition of 2,4-D uptake, suggesting proton symport as the likely active mechanism. …
NAID 130000029813

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★リンクテーブル★

リンク元	「ion transport」「active ion transport」「cotransport」「co-transport」「共輸送」
拡張検索	「sodium-bicarbonate symporter」「sodium-potassium-chloride symporter inhibitor」「sodium-potassium-chloride symporter」