Sequential Amino Acid Exchange across b0,+-like System in Chicken Brush Border Jejunum |
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Authors: | M Torras-Llort D Torrents JF Soriano-García JL Gelpí R Estévez R Ferrer M Palacín M Moretó |
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Institution: | (1) Departament de Fisiologia-Divisió IV, Facultat de Farmàcia, Universitat de Barcelona, Av. Joan XXIII s/n, 08028 Barcelona, Spain, ES;(2) Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain, ES |
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Abstract: | In the small intestine, cationic amino acids are transported by y+-like and b0,+-like systems present in the luminal side of the epithelium. Here, we report the characterization of a b0,+-like system in the apical membrane of the chicken jejunum, and its properties as an amino acid exchanger. Analysis of the
brush border membrane by Western blot points out the presence of rBAT (protein related to b0,+ amino acid transport system) in these membranes. A functional mechanism for amino acid exchange across this system was established
by kinetic analysis measuring fluxes at varying substrate concentrations both in internal (in) and external (out) vesicle
compartments. This intestinal b0,+-like system functions for l-arginine as an obligatory exchanger since its transport capacity increases 100–200 fold in exchange conditions, thus suggesting
an important role in the intestinal absorption of cationic amino acids. The kinetic analysis of Argin efflux velocities is compatible with the formation of a ternary complex and excludes a model involving a ping-pong mechanism. The binding affinity of Argout is higher than that of Argin, suggesting a possible order of binding (Argout first) for the formation of the ternary complex during the exchange cycle. A model of double translocation pathways with
alternating access is discussed.
Received: 23 March 2000/Revised: 29 December 2000 |
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Keywords: | :l-arginine — Kinetic mechanism — Homoexchange — Heteroexchange — rBAT — Vesicles |
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