Symporter
Encyclopedia
A cotransporter is an integral membrane protein
that is involved in secondary active transport
. It works by binding to two molecule
s or ions at a time and using the gradient
of one solute
's concentration
to force the other molecule or ion against its gradient.
It is sometimes equated with symporter
, a word made up of a conjunction of the Greek syn- or sym- for "together, with" (cf. symphony, synonym) and -porter. Symporter is also sometimes misspelled simporter because of the simultaneous transport of molecules (and the phonetic resemblance to symporter).
In order for any protein
to do work
, it must harness energy
from some source. In particular, symporters do not require the splitting of ATP
because they derive the necessary energy for the movement of one molecule from the movement of the another. Overall, the movement of the two molecules still acts to increase entropy
.
Proton-sucrose cotransporters are common in plant cell membranes. An ATP molecule in the cell phosphorylates a carrier protein, causing a conformational change that shuttles a proton across the membrane. The proton binds with sucrose in the extracellular fluid, then undergoes passive transport down its concentration gradient (i.e. up the concentration gradient of sucrose).
In August 1960, in Prague, Robert K. Crane
presented for the first time his discovery of the sodium-glucose cotransport
as the mechanism for intestinal glucose absorption. Crane
's discovery of cotransport
was the first ever proposal of flux coupling in biology.
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 involved in secondary active transport
Active transport
Active 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...
. It works by binding to two molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s or ions at a time and using the 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....
of one solute
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
's concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
to force the other molecule or ion against its gradient.
It is sometimes equated with symporter
Symporter
A cotransporter is an integral membrane protein that is involved in secondary active transport. It works by binding to two molecules or ions at a time and using the gradient of one solute's concentration to force the other molecule or ion against its gradient....
, a word made up of a conjunction of the Greek syn- or sym- for "together, with" (cf. symphony, synonym) and -porter. Symporter is also sometimes misspelled simporter because of the simultaneous transport of molecules (and the phonetic resemblance to symporter).
In order for any protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
to do work
Mechanical work
In physics, work is a scalar quantity that can be described as the product of a force times the distance through which it acts, and it is called the work of the force. Only the component of a force in the direction of the movement of its point of application does work...
, it must harness energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
from some source. In particular, symporters do not require the splitting of ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
because they derive the necessary energy for the movement of one molecule from the movement of the another. Overall, the movement of the two molecules still acts to increase entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
.
Proton-sucrose cotransporters are common in plant cell membranes. An ATP molecule in the cell phosphorylates a carrier protein, causing a conformational change that shuttles a proton across the membrane. The proton binds with sucrose in the extracellular fluid, then undergoes passive transport down its concentration gradient (i.e. up the concentration gradient of sucrose).
In August 1960, in Prague, Robert K. Crane
Robert K. Crane
Robert Kellogg Crane is an American biochemist best known for his discovery of sodium-glucose cotransport.-Biography:...
presented for the first time his discovery of the sodium-glucose cotransport
Co-transport
Co-transport, also known as coupled transport or secondary active transport, refers to the simultaneous or sequential passive transfer of molecules or ions across biological membranes in a fixed ratio...
as the mechanism for intestinal glucose absorption. Crane
Robert K. Crane
Robert Kellogg Crane is an American biochemist best known for his discovery of sodium-glucose cotransport.-Biography:...
's discovery of cotransport
Co-transport
Co-transport, also known as coupled transport or secondary active transport, refers to the simultaneous or sequential passive transfer of molecules or ions across biological membranes in a fixed ratio...
was the first ever proposal of flux coupling in biology.
See also
- Na-K-2Cl symporterNa-K-2Cl symporterThe Na-K-Cl cotransporter is a protein that aids in the active transport of sodium, potassium, and chloride into and out of cells. There are two varieties, or isoforms, of this membrane transport protein, called NKCC1 and NKCC2. NKCC1 is widely distributed throughout the body; it has important...
- K-Cl cotransporter
- Sodium/phosphate cotransporterSodium/phosphate cotransporterThe sodium/phosphate cotransporter is a protein found in the proximal tubule of the nephron. It is responsible for reabsorbing phosphate that has been filtered out at the glomerulus.-See also:* Renal physiology* Cotransporter...
- Sodium-glucose transport proteinsSodium-glucose transport proteinsSodium-dependent glucose cotransporters are a family of glucose transporter found in the intestinal mucosa of the small intestine and the proximal tubule of the nephron . They contribute to renal glucose reabsorption...
- Glucose transporterGlucose transporterGlucose transporters are a wide group of membrane proteins that facilitate the transport of glucose over a plasma membrane. Because glucose is a vital source of energy for all life these transporters are present in all phyla...
- Co-transportCo-transportCo-transport, also known as coupled transport or secondary active transport, refers to the simultaneous or sequential passive transfer of molecules or ions across biological membranes in a fixed ratio...