Different Transport Mechanisms in Plant and Human AMT/Rh-type Ammonium Transporters
| Autor: | Jean-Pierre Cartron, Yves Colin, Petra Neumann, Claude Lopez, Uwe Ludewig, Maria Mayer, I Mouro, Gabriel Schaaf |
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| Rok vydání: | 2006 |
| Předmět: |
inorganic chemicals
Patch-Clamp Techniques Physiology Xenopus Saccharomyces cerevisiae Article Membrane Potentials Methylamines chemistry.chemical_compound Solanum lycopersicum Ammonia Animals Humans Ammonium Cation Transport Proteins Plant Proteins Ion Transport Membrane Glycoproteins biology Membrane transport protein food and beverages Articles Hydrogen-Ion Concentration biology.organism_classification Yeast Quaternary Ammonium Compounds Cytosol chemistry Biochemistry RHCG Oocytes biology.protein Biophysics Female Heterologous expression Ammonium transport |
| Zdroj: | The Journal of General Physiology |
| ISSN: | 1540-7748 0022-1295 |
| DOI: | 10.1085/jgp.200509369 |
| Popis: | The conserved family of AMT/Rh proteins facilitates ammonium transport across animal, plant, and microbial membranes. A bacterial homologue, AmtB, forms a channel-like structure and appears to function as an NH3 gas channel. To evaluate the function of eukaryotic homologues, the human RhCG glycoprotein and the tomato plant ammonium transporter LeAMT1;2 were expressed and compared in Xenopus oocytes and yeast. RhCG mediated the electroneutral transport of methylammonium (MeA), which saturated with Km = 3.8 mM at pHo 7.5. Uptake was strongly favored by increasing the pHo and was inhibited by ammonium. Ammonium induced rapid cytosolic alkalinization in RhCG-expressing oocytes. Additionally, RhCG expression was associated with an alkali-cation conductance, which was not significantly permeable to NH4+ and was apparently uncoupled from the ammonium transport. In contrast, expression of the homologous LeAMT1;2 induced pHo-independent MeA+ uptake and specific NH4+ and MeA+ currents that were distinct from endogenous currents. The different mechanisms of transport, including the RhCG-associated alkali-cation conductance, were verified by heterologous expression in appropriate yeast strains. Thus, homologous AMT/Rh-type proteins function in a distinct manner; while LeAMT1;2 carries specifically NH4+, or cotransports NH3/H+, RhCG mediates electroneutral NH3 transport. |
| Databáze: | OpenAIRE |
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