In biology, an ion transporter, also called an ion pump, is a transmembrane protein that moves ions across a plasma membrane against their concentration gradient, in contrast to ion channels, where ions go through passive transport. These primary transporters are enzymes that convert energy from various sources, including ATP, sunlight, and other redox reactions, to potential energy stored in an electrochemical gradient. This energy is then used by secondary transporters, including ion carriers and ion channels, to drive vital cellular processes, such as ATP synthesis.
Such ion pumps can use energy from a variety of sources, including ATP or the concentration gradient of another ion (sometimes called an "ion exchanger"). Symporters transport anions down their concentration gradient to fuel the transport of another type of ion in the same direction, while antiporters also use the concentration gradient in this same manner but transport in the opposite direction. In contrast, uniporters transport a single ion down its concentration gradient. In all of these cases, there is at least one driving ion that travels down its concentration gradient, thereby providing the energy of the system. Ions that are moved up their concentration gradients are called the driven ion. For a more detailed description of one particular kind of ion pump, see Na+/K+-ATPase.