Electroneutral ammonium transport by basolateral rhesus B glycoprotein
1Pflanzenphysiologie, Zentrum für Molekularbiologie der Pflanzen, Universität Tübingen, Auf der Morgenstelle 1, D-72076, Germany. uwe.ludewig@zmbp.uni-tuebingen.de
The Journal of Physiology
|July 31, 2004
Summary
Rhesus B glycoprotein (RhBG) facilitates electroneutral ammonium transport in the kidney. This protein functions as an ammonium-hydrogen exchanger, crucial for kidney and liver ammonium metabolism.
Area of Science:
- Physiology
- Molecular Biology
- Biochemistry
Background:
- The liver and kidney are key organs for ammonium (NH4+/NH3) metabolism and excretion.
- Rhesus B glycoprotein (RhBG) is a membrane protein found in the liver and kidney, structurally similar to ammonium transporters.
- In the kidney, RhBG is primarily located in the basolateral membranes of distal tubule epithelia.
Purpose of the Study:
- To investigate the transport mechanism of RhBG.
- To determine if RhBG mediates electroneutral ammonium transport.
- To characterize the kinetic properties and functional role of RhBG in ammonium transport.
Main Methods:
- Heterologous expression of human RhBG in Xenopus oocytes.
- Measurement of methylammonium uptake kinetics.
- Inhibition studies using ammonium.
- Electrophysiological measurements and intracellular pH monitoring.
Main Results:
- Human RhBG mediates saturable, electroneutral transport of methylammonium.
- Methylammonium uptake exhibits Michaelis-Menten kinetics with a Km of 2.6 mM.
- Ammonium inhibits methylammonium uptake with a Ki of approximately 3 mM.
- Data suggest RhBG functions as an electroneutral NH4+-H+ exchanger.
Conclusions:
- RhBG plays a significant role in kidney ammonium transport.
- The protein facilitates electroneutral ammonium-hydrogen exchange in distal tubule epithelia.
- RhBG's function is critical for maintaining ammonium homeostasis in the kidney.
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