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rBAT is an amino acid exchanger with variable stoichiometry
M J Coady1, X Z Chen, J Y Lapointe
1Département de Physique, Université de Montréal, QC, Canada.
The Journal of Membrane Biology
|January 1, 1996
Summary
The rBAT protein facilitates amino acid transport by requiring substrates on both sides of the membrane. However, influx and efflux are not stoichiometrically linked, suggesting a novel "double gated pore" mechanism for amino acid exchange.
Area of Science:
- Biochemistry
- Molecular Biology
- Membrane Transport
Background:
- The rBAT protein mediates Na(+)-independent transport of neutral and basic amino acids.
- Previous studies showed rBAT generates transmembrane currents upon neutral amino acid addition, stimulating cation efflux.
Purpose of the Study:
- To investigate the transport mechanism of the rBAT protein using aminoisobutyric acid (AIB).
- To challenge the classical exchanger model for rBAT function.
Main Methods:
- Xenopus oocyte expression system.
- Electrophysiological recordings using cut-open oocyte voltage clamp.
- Measurement of radiolabeled amino acid efflux.
Main Results:
- AIB induced outward currents similar to alanine, indicating similar affinity and maximal currents.
- AIB transport rate was significantly lower than alanine, questioning classical exchanger function.
- AIB stimulated efflux of both radiolabeled alanine and arginine from both sides of the membrane.
- Amino acid flux required substrates on both sides, but influx was not stoichiometrically related to efflux.
Conclusions:
- rBAT functions as an exchanger, requiring amino acids on both sides of the membrane.
- The non-stoichiometric relationship between influx and efflux suggests a novel transport mechanism.
- A "double gated pore" model is proposed for rBAT function, diverging from standard transporter models.