Characterization of a binding protein-dependent glutamate transport system of Rhodobacter sphaeroides.
The mechanism of L-glutamate uptake was studied in Rhodobacter sphaeroides. Uptake of L-glutamate is mediated by a high-affinity (Kt of 1.2 microM), shock-sensitive transport system that is inhibited by vanadate and dependent on the internal pH. From the shock fluid, an L-glutamate-binding protein was isolated and purified. The protein binds L-glutamate (apparent Kd of 1.3 microM) and L-glutamine (Ki of 15 microM) with high affinity. The expression level of this binding protein is maximal at limiting concentrations of glutamine in the growth medium. The glutamate-binding protein restores the uptake of L-glutamate in spheroplasts. L-Aspartate is a strong competitive inhibitor of L-glutamate uptake (Ki of 3 microM) but competes only poorly with L-glutamate for binding to the binding protein (Ki of > 200 microM). The uptake of L-aspartate in R. sphaeroides also involves a binding protein which is distinct from the L-glutamate-binding protein. These data suggest that in R. sphaeroides, the L-glutamate- and L-aspartate-binding proteins interact with the same membrane transporter.
Jacobs
M H
MH
Department of Microbiology, University of Groningen, Haren, The Netherlands.
Driessen
A J
AJ
Konings
W N
WN
D000255:Adenosine Triphosphate / Q000378:metabolism; D001224:Aspartic Acid / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013379:Substrate Specificity; D014638:Vanadates / Q000494:pharmacology
D002352:Carrier Proteins; D001224:Aspartic Acid; D018698:Glutamic Acid; D014638:Vanadates; D000255:Adenosine Triphosphate