Characterization of tryptophan transport in human placental brush-border membrane vesicles

M. E. Ganapathy, F. H. Leibach, V. B. Mahesh, J. C. Howard, Lawrence D Devoe

Research output: Contribution to journalArticle

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Abstract

The characteristics of tryptophan uptake in isolated human placental brush-border membrane vesicles were investigated. Tryptophan uptake in these vesicles was predominantly Na+-independent. Uptake of tryptophan as measured with short incubations occurred exclusively by a carrier-mediated process, but significant binding of this amino acid to the membrane vescicles was observed with longer incubations. The carrier-mediated system obeyed Michaelis-Menten kinetics, with an apparent affinity constant of 12.7 ± 1.0 μM and a maximal velocity of 91 ± 5 pmol/15 s per mg of protein. The kinetic constants were similar in the presence and absence of a Na+ gradient. Competition experiments showed that tryptophan uptake was effectively inhibited by many neutral amino acids except proline, hydroxyproline and 2-(methylamino)isobutyric acid. The inhibitory amino acids included aromatic amino acids as well as other system-1-specific amino acids (system 1 refers to the classical L system, according to the most recent nomenclature of amino acid transport systems). The transport system showed very low affinity for D-isomers, was not affected by phloretin or glucose but was inhibited by p-azidophenylalanine and N-ethylmaleimide. The uptake rates were only minimally affected by change in pH over the range 4.5-8.0. Tryptophan uptake markedly responded to trans-stimulation, and the amino acids capable of causing trans-stimulation included all amino acids with system-1-specificity. The patterns of inhibition of uptake of tryptophan and leucine by various amino acids were very similar. We conclude that system t, which is specific for aromatic amino acids, is absent from human placenta and that tryptophan transport in this tissue occurs via system 1, which has very broad specificity.

Original languageEnglish (US)
Pages (from-to)201-208
Number of pages8
JournalBiochemical Journal
Volume238
Issue number1
DOIs
StatePublished - Jan 1 1986
Externally publishedYes

Fingerprint

Brushes
Microvilli
Tryptophan
Membranes
Amino Acids
Aromatic Amino Acids
tryptophan-leucine
Phloretin
Neutral Amino Acids
Amino Acid Transport Systems
Kinetics
Ethylmaleimide
Hydroxyproline
Terminology
Proline
Isomers
Placenta
Tissue
Glucose
Proteins

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

Characterization of tryptophan transport in human placental brush-border membrane vesicles. / Ganapathy, M. E.; Leibach, F. H.; Mahesh, V. B.; Howard, J. C.; Devoe, Lawrence D.

In: Biochemical Journal, Vol. 238, No. 1, 01.01.1986, p. 201-208.

Research output: Contribution to journalArticle

Ganapathy, M. E. ; Leibach, F. H. ; Mahesh, V. B. ; Howard, J. C. ; Devoe, Lawrence D. / Characterization of tryptophan transport in human placental brush-border membrane vesicles. In: Biochemical Journal. 1986 ; Vol. 238, No. 1. pp. 201-208.
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