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Tryptophan Transport into Plasma Membrane Vesicles Derived from Rat Brain Synaptosomes

Authors

  • E. Herrero,

    1. Departamento de Bioquímica y Biología Molecular, Centra de Biología Molecular, Facultad de Ciencias, Universidad Autónoma, Madrid, Spain
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  • M. C. Aragón,

    1. Departamento de Bioquímica y Biología Molecular, Centra de Biología Molecular, Facultad de Ciencias, Universidad Autónoma, Madrid, Spain
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  • C. Giménez,

    1. Departamento de Bioquímica y Biología Molecular, Centra de Biología Molecular, Facultad de Ciencias, Universidad Autónoma, Madrid, Spain
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  • F. Valdivieso

    Corresponding author
    1. Departamento de Bioquímica y Biología Molecular, Centra de Biología Molecular, Facultad de Ciencias, Universidad Autónoma, Madrid, Spain
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Address correspondence and reprint requests to Prof. Fernando Valdivieso, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad Autónoma, Madrid-34, Spain.

Abstract

Abstract: Tryptophan uptake by membrane vesicles derived from rat brain was investigated. The uptake is dependent on the Na+ gradient [Na+] outside > [Na+] inside and is maximal when both Na+ and Cl are present. The uptake represents transport into an os-motically active space and not a binding artifact, as indicated by the effect of increasing the medium osmo-larity. The uptake of tryptophan is stimulated by a membrane potential (interior negative) as demonstrated by the effects of the ionophores valinomycin and carbonyl cyanide m-chlorophenylhydrazone and anions with different permeabilities. Kinetic data show that tryptophan is accumulated by two systems with different affinities. Ouabain, an inhibitor of Na+, K+-activated ATPase, does not affect tryptophan transport. The uptake of tryptophan is inhibited by high concentrations of phenylalanine, tyrosine, leucine and 3, 4-dihydroxyphenylalanine.

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