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

TY - JOUR

T1 - Ammonium ion transport by the AMT/Rh homolog TaAMT1;1 is stimulated by acidic pH

AU - Søgaard, Rikke

AU - Alsterfjord, Magnus

AU - Macaulay, Nanna

AU - Zeuthen, Thomas

PY - 2009

Y1 - 2009

N2 - 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.

AB - 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.

U2 - 10.1007/s00424-009-0665-z

DO - 10.1007/s00424-009-0665-z

M3 - Journal article

C2 - 19340454

SN - 0031-6768

VL - 458

SP - 733

EP - 743

JO - Pflügers Archiv - European Journal of Physiology

JF - Pflügers Archiv - European Journal of Physiology

IS - 4

ER -