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  • Title: Uphill transport of beta-alanine in intestinal brush-border membrane vesicles.
    Author: Miyamoto Y, Nakamura H, Hoshi T, Ganapathy V, Leibach FH.
    Journal: Am J Physiol; 1990 Sep; 259(3 Pt 1):G372-9. PubMed ID: 2119146.
    Abstract:
    The characteristics of beta-alaline uptake were studied in brush-border membrane vesicles isolated from the proximal small intestine of rabbits and were compared with those of L-alpha-alanine uptake. The uptake of beta-alanine as well as L-alpha-alanine was significantly stimulated by imposing an inwardly directed Na+ gradient. Studies on transstimulation and substrate specificity provide evidence that the transport system serving beta-alanine is distinct from the system serving alpha-alanine. The beta-system also accepts taurine as a substrate. The Na(+)-dependent uptakes of beta-alanine and L-alpha-alanine were differentially influenced by anions. The order in which anions supported uptake was Cl- = SCN- greater than F- greater than NO3- = SO2(-4) for beta-alanine, whereas it was SCN- greater than F- = Cl- = NO3- greater than SO2(-4) for L-alpha-alanine. Cl- appeared to be the preferred anion to support the uptake of beta-alanine. beta-Alanine uptake was greater in the presence of an inwardly directed Cl- gradient than in the presence of Cl- at equal concentrations on both sides of the membrane. The uptake was maximal when a Na+ gradient and a Cl- gradient were present simultaneously. The NaCl gradient-driven beta-alanine uptake was stimulated by an inside-negative K(+)-diffusion potential induced by valinomycin, showing that the uptake process is electrogenic. Stoichiometric analyses suggest that multiple Na+ and one Cl- are associated with the uptake of one beta-alanine molecule. The kinetic study shows that the transporter for beta-alanine is a high-affinity, low-capacity system (Kt = 46 +/- 1 microM; Vmax = 30 +/- 1 pmol.mg protein-1.15 s-1).
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