Primary Active Transporters. These transporters use a primary source of energy to drive active transport of a solute against a concentration gradient. A secondary ion gradient is not considered a primary energy source because it is created by the expenditure of a primary energy source. Primary energy sources known to be coupled to transport are chemical, electrical and solar.
3.A. P-P-bond hydrolysis-driven transporters. Transport systems are included in this subclass if they hydrolyze the diphosphate bond of inorganic pyrophosphate, ATP, or another nucleoside triphosphate, to drive the active uptake and/or extrusion of a solute or solutes. The transport protein may or may not be transiently phosphorylated, but the substrate is not phosphorylated.
3.B. Decarboxylation-driven transporters. Transport systems that drive solute (e.g., ion) uptake or extrusion by decarboxylation of a cytoplasmic substrate are included in this subclass. These transporters are currently thought to be restricted to prokaryotes.
3.C. Methyltransfer-driven transporters. A single characterized multisubunit protein family currently falls into this subclass, the Na+-transporting methyltetrahydromethanopterin:coenzyme M methyltransferase. These transporter complexes are currently thought to be restricted to archaea.
3.D. Oxidoreduction-driven transporters. Transport systems that drive transport of a solute (e.g., an ion) energized by the exothermic flow of electrons from a reduced substrate to an oxidized substrate are included in this subclass.
3.E. Light absorption-driven transporters. Transport systems that utilize light energy to drive transport of a solute (e.g., an ion) are included in this subclass.