All functionally characterised members of the ammonium transporter family are ammonia or ammonium uptake transporters. Some, but not others, also transport methylammonium. Uptake of ammonium/ammonia by AtmB protein from E. coli is electrogenic. Following sequestration of NH4+ at the periplasmic face, NH4+ is deprotonated and neutral NH3 is transported into the cytoplasm. Neutral NH3 and charged H+ are carried separately across the membrane on a unique two-lane pathway, before recombining to NH4+ inside the cell. It also acts as a sensor of the extracellular ammonium concentration [, ].This entry represents ammonium transporters belonging to the Amt family, but it does not include the Rhesus (Rh) subgroup.
