Uniport of NH4+ by the root hair plasma membrane ammonium transporter LeAMT1;1
Uniport of NH4+ by the root hair plasma membrane ammonium transporter LeAMT1;1
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DOI：
10.1074/jbc.m200739200
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发表时间：
2002-04-19
影响因子：
4.8
通讯作者：
Frommer, WB
中科院分区：
文献类型：
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作者：
Ludewig, U;von Wirén, N;Frommer, WB
铵/氨的转运是氮素获取和代谢的关键过程。铵转运由AMT/MEP/Rh膜蛋白家族介导，这些膜蛋白在微生物、植物和动物中发现，包括人类中的恒河猴血型抗原。虽然所有王国的铵转运蛋白已被功能表达和部分表征，运输机制，以及真正的底物（NH 4+或NH3）的身份仍然不清楚。在这里，我们描述了LeAMT 1：1，从番茄（番茄）根毛铵转运蛋白在非洲爪蟾卵母细胞的功能表达和表征。微摩尔浓度的外部铵被发现诱导浓度和电压依赖性内向电流的卵母细胞注射LeAMT 1;1 cRNA，但不是在水注射的控制卵母细胞。NH 4+诱导的电流比甲基铵电流大3倍以上，并且不受Na+或K+的抑制。LeAMT 1;1对其底物的亲和力的电压依赖性强烈表明，带电的NH 4+而不是NH3才是真正的4转运底物。此外，铵运输是独立的外部质子浓度之间的pH 5.5和pH 8.5。LeAMT 1;1介导电位驱动的NH 4+吸收和回收依赖于根膜电位和NH 4+浓度梯度。
The transport of ammonium/ammonia is a key process for the acquisition and metabolism of nitrogen. Ammonium transport is mediated by the AMT/MEP/Rh family of membrane proteins which are found in microorganisms, plants, and animals, including the Rhesus blood group antigens in humans. Although ammonium transporters from all kingdoms have been functionally expressed and partially characterized, the transport mechanism, as well as the identity of the true substrate (NH4+ or NH3) remains unclear. Here we describe the functional expression and characterization of LeAMT1:1, a root hair ammonium transporter from tomato (Lycopersicon esculentum) in Xenopus oocytes. Micromolar concentrations of external ammonium were found to induce concentration- and voltage-dependent inward currents in oocytes injected with LeAMT1;1 cRNA, but not in water-injected control oocytes. The NH4+-induced currents were more than 3-fold larger than methylammonium currents and were not subject to inhibition by Na+ or K+. The voltage dependence of the affinity of LeAMT1;1 toward its substrate strongly suggests that charged NH4+, rather than NH3, is the true 4 transport substrate. Furthermore, ammonium transport was independent of the external proton concentration between pH 5.5 and pH 8.5. LeAMT1;1 is concluded to mediate potential-driven NH4+ uptake and retrieval depending on root membrane potential and NH4+ concentration gradient.