Sunday, October 18, 2009
symport- -celltransport-cellbiology-4th unit-btechbiotechnology-jntusyllabus-2-1
An antiporter (also called exchanger or counter-transporter) is an integral membrane protein which is involved in secondary active transport of two or more different molecules or ions (i.e. solutes) across a phospholipid membrane such as the plasma membrane in opposite directions.
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, used by many cells to remove cytoplasmic calcium, exchanges one calcium ion for three sodium ions.
The sodium-calcium exchanger (often denoted Na+/Ca2+ exchanger, NCX, or exchange protein) is an antiporter membrane protein which removes calcium from cells. It uses the energy that is stored in the electrochemical gradient of sodium (Na+) by allowing Na+ to flow down its gradient across the plasma membrane in exchange for the countertransport of calcium ions (Ca2+). The NCX removes a single calcium ion in exchange for the import of three sodium ions. The exchanger exists in many different cell types and animal species. The NCX is considered one of the most important cellular mechanisms for removing Ca2+.
The exchanger is usually found in the plasma membranes and the mitochondria and endoplasmic reticulum of excitable cells.