Uphill transport of beta-alanine in intestinal brush-border membrane vesicles.
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).
Miyamoto
Y
Y
Department of Physiology, School of Food and Nutritional Sciences, University of Shizuoka, Japan.
Nakamura
H
H
Hoshi
T
T
Ganapathy
V
V
Leibach
F H
FH
D000409:Alanine / Q000378:metabolism*; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000494:pharmacology; D004386:Duodenum / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D007700:Kinetics; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D015091:beta-Alanine / Q000378:metabolism*
D000596:Amino Acids; D002712:Chlorides; D015091:beta-Alanine; D012964:Sodium; D000409:Alanine