Journal Article

Proton-Symport of <span class="smallCaps">l</span>-Valine in Plasma Membrane Vesicles Isolated from Leaves of the Wild-Type and the Val<sup>r</sup>-2 Mutant of <i>Nicotiana tabacum</i> L.

Adrianus C. Borstlap and Jolanda A.M.J. Schuurmans

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 41, issue 11, pages 1210-1217
Published in print November 2000 | ISSN: 0032-0781
Published online November 2000 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcd058
Proton-Symport of l-Valine in Plasma Membrane Vesicles Isolated from Leaves of the Wild-Type and the Valr-2 Mutant of Nicotiana tabacum L.

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Transport of amino acids across the plasma membranes of various cell types is a key process in controlling the nitrogen balance of leaves. We studied the transport of the neutral amino acid l-valine into plasma membrane vesicles obtained by aqueous polymer two-phase partitioning of a microsomal fraction isolated from leaves of the wild-type and the Valr-2 mutant of tobacco (Nicotiana tabacum L.). Initial influxes were determined after the imposition of a pH-gradient (ΔpH, inside alkaline) and/or an electrical gradient (Δψ, inside negative) across the vesicle membrane. The initial magnitudes of the imposed gradients were ΔpH=2 and Δψ=−68 mV. In vesicles from the wild-type, the ΔpH-dependent valine influx could be analysed into a high-affinity (Km ≈20 µM) and a low-affinity (Km ≈3 mM) component. The influx of valine by the low-affinity system was stimulated about twofold, and that by the high-affinity system more than sixfold by the imposition of Δψ. This strong stimulation of the high-affinity system may indicate that it transports 2H+/amino acid. In the Valr-2 mutant the high-affinity component appeared to be completely absent.

Keywords: Key words: Amino acids — H+-symport — Membrane transport — Nicotiana tabacum L. — Plasma membrane vesicles — Valine resistant mutant.; Abbreviations: BSA, bovine serum albumin; CCCP, carbonyl cyanide m-chlorophenyl-hydrazone; DTT, dithiothreitol.

Journal Article.  5766 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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