Transporter (membrane protein)
Transporters (also: Carrier ) are membrane-based transport proteins , the main transport process of which is coupled with the single transport ( carrier or permeases for the Uniport ; example: GLUT1 ) of a solute or with a second transport process ( Symport , Antiport; example: SGLT1 ) through a conformational change . Transporters differ from the completely passive channel- and pore-forming proteins (since a conformational change is necessary for transport) and from the active ATPases (active energy consumption). In the case of the Uniport, one speaks of facilitated diffusion and of the Sym- and Antiport of secondary active transport. Many transport proteins that are important for all living beings belong to the transporters. They form subclass 2.A. in the TCDB classification.
Membrane proteins, which function according to a symport mechanism, transport the substrate and the coupling ion in the same direction. If, on the other hand, two substrates are transported in opposite directions, one speaks of an anti-port system.
Important families within the transporter subclass are the major facilitator proteins (with the glucose transporters ), the solutes: sodium symporters (SSS), the mitochondrial carriers , the chloride carriers / channels , the organo-anion transporters and the oligopeptide transporters .