Endogenous L-glutamate transport in oocytes of Xenopus laevis.
The existence of an endogenous Na(+)-glutamate cotransporter in the oocytes of Xenopus laevis is demonstrated. The transporter does not accept D-glutamate as substrate. The dependence on substrate displays two saturating components with low (K1/2 = 9 mM) and high (K1/2 = 0.35 microM) affinities for L-glutamate. The dependence on external Na+ exhibits a saturating component with a K1/2 value of about 5 mM and a component that has not saturated up to 110 mM Na+. In voltage-clamped oocytes, it is possible to demonstrate that Na(+)-dependent L-glutamate transport is directly coupled to countertransport of Rb+. The analysis of the voltage dependence of the Na+,K(+)-dependent L-glutamate uptake suggests that positive charges are moved inwardly during the transport cycle.
Max-Planck-Institut für Biophysik, Frankfurt/Main, F.R.G.
J
J
Steffgen
H
H
Koepsell
W
W
Schwarz
D027322:Amino Acid Transport System X-AG; D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D004563:Electrochemistry; D005260:Female; D050491:Glutamate Plasma Membrane Transport Proteins; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D066298:In Vitro Techniques; D007700:Kinetics; D009865:Oocytes / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013379:Substrate Specificity; D027981:Symporters; D014982:Xenopus laevis
D027322:Amino Acid Transport System X-AG; D002352:Carrier Proteins; D050491:Glutamate Plasma Membrane Transport Proteins; D005971:Glutamates; D027981:Symporters; D018698:Glutamic Acid; D012964:Sodium; D012413:Rubidium