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Characterization of a glutamine/proton cotransporter from Ricinus comnmnis roots using isolated plasma membrane vesicles
Author(s) -
Weston Kim,
Hall J.L.,
Williams Lorraine E.
Publication year - 1994
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1994.tb02997.x
Subject(s) - glutamine , biochemistry , chemistry , membrane , facilitated diffusion , biophysics , vesicle , membrane transport , ricinus , proton transport , symporter , biology , transporter , amino acid , gene
The mechanism of glutamine transport at the plasma membrane of sink tissue cells was investigated using isolated plasma membrane vesicles from roots of Ricinus communis L. var. sanguineous . Glutamine transport was found to be driven by both the pH gradient (ΔpH) and a membrane potential (ΔΨ) (alkaline and negative internal), which were created artificially across the plasma membrane. Glutamine wus accumulated 15–20‐fold in the presence of both a ΔpH and Δ Ψ . There appeared to be a direct pH effect on Δ PS ‐driven transport, as a higher rate of transport was observed at pH 5.5 than at pH 7.5. The ΔpH +Δ Ψ ‐driven transport showed saturation kinetics with a K m of 287 μ M . Altering the membrane potential changed the V max but had no effect on the K m of glutamine transport. These results are consistent with the presence of a proton‐coupled, carrier‐mediated system for glutamine uptake in Ricinus roots. A range of protein modifiers and transport inhibitors had limited effects on glutamine transport: highest inhibition uas observed with cytochalasin D. When glutamine transport was compared in plasma membrane vesicles isolated from the root lips of Ricinus and from the remainder of the root tissue a lower level of transport was observed in the root tips. A method for the solubilization and reconstitution of glutamine transport activity using the detergent CHAPS is also described.