Ammonium ion transport by the AMT/Rh homolog TaAMT1;1 is stimulated by acidic pH

作者：Sogaard Rikke; Alsterfjord Magnus; MacAulay Nanna; Zeuthen Thomas^*

来源：Pflugers Archiv-European Journal of Physiology, 2009, 458(4): 733-743.

DOI：10.1007/s00424-009-0665-z

• Ammonium transporters
• Molecular model
• pH dependence
• Xenopus oocytes
• Voltage clamp
• Amt/Mep/Rh superfamily
• Electrophysiology

It is unclear how ammonia is transported by proteins from the Amt/Mep/Rh superfamily. We investigated this for the ammonium transporter TaAMT1;1 from wheat expressed in Xenopus oocytes by two-electrode voltage clamp and radio-labeled uptakes. Inward currents were activated by NH (4) ( ) or methylammonium ions (MeA( )). Importantly, currents increased fivefold when the external pH was decreased from 7.4 to 5.5; this type of pH dependence is unique and is a strong indication of NH (4) ( ) or MeA( ) transport. This was confirmed by the close correlation between the uptake of radio-labeled MeA( ) and MeA( )-induced currents. Homology models of members of the Amt/Mep/Rh superfamily exhibited major divergences in their cytoplasmic regions. A point mutation in this region of TaAMT1;1 abolished the pH sensitivity and decreased the apparent affinities for NH (4) ( ) and MeA( ). We suggest a model where NH (4) ( ) is transported as NH(3) and H( ) via separate pathways but the latter two recombine before leaving the protein.

• 出版日期2009-8