Sodium-Ion Stimulated Amino Acid Uptake in Membrane Vesicles of Alkalophilic Bacillus No. 8–1

The transport of L-alanine and L-leucine into membrane vesicles isolated from mature canine ventricular myocardium was studied. Transport was assessed in purified sarcolemma and in vesicles differentially enriched either for sarcolemma or sarcoplasmic reticulum to further localize these transport systems. An imposed inward gradient of a NaNO3 stimulated uptake of L-alanine but not L-leucine by these vesicles. Amino acid uptake by these vesicles occurred into an osmotically active space. The stimulatory effect of Na+ on alanine transport was most striking in the purified sarcolemma vesicles, where Na+-stimulated alanine flux was 45 +/- 14 pmol X mg-1 X min-1. Furthermore, Na+-dependent alanine transport activity appeared to copurify with Na+-K+-ATPase activity, which served as a marker for sarcolemma membrane when these activities were compared in the three different membrane preparations. Leucine transport by sarcolemma was not altered by an imposed Na+ gradient. However, leucine uptake was a saturable function of extravesicular leucine and was inhibited by valine. In contrast, in sarcoplasmic reticulum membrane vesicles leucine uptake increased proportionately with increasing media leucine and was unaffected by valine. Our results demonstrate the feasibility of directly studying the transport of naturally occurring amino acids in membrane vesicles from mammalian heart, and the presence of Na+-dependent alanine transport system and a Na+-independent leucine transporter in the sarcolemma but not in sarcoplasmic reticulum of canine ventricular myocardium.

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Amino acid uptake by Saccharomyces cerevisiae plasma membrane vesicles

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/0005-2736(80)90252-7 ◽

1980 ◽

Vol 595 (1) ◽

pp. 109-120 ◽

Cited By ~ 9

Author(s):

Glenn J. Merkel ◽

Fred Naider ◽

Jeffrey M. Becker

Keyword(s):

Saccharomyces Cerevisiae ◽

Plasma Membrane ◽

Amino Acid ◽

Membrane Vesicles ◽

Amino Acid Uptake ◽

Acid Uptake ◽

Plasma Membrane Vesicles

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Anionic amino acid uptake by microvillous membrane vesicles from human placenta

AJP Cell Physiology ◽

10.1152/ajpcell.1989.257.5.c1005 ◽

1989 ◽

Vol 257 (5) ◽

pp. C1005-C1011 ◽

Cited By ~ 91

Author(s):

A. J. Moe ◽

C. H. Smith

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Glutamate Uptake ◽

Membrane Vesicles ◽

Amino Acid Uptake ◽

Maternal Blood ◽

Acid Uptake ◽

Dependent Manner ◽

Concentration Dependent Manner

The transport mechanisms for anionic amino acids in trophoblast microvillous (maternal facing) membrane were investigated by characterization of L-[3H]aspartate and L-[3H]glutamate uptake in membrane vesicles. Uptake of the anionic amino acids was by a single high-affinity Na+-dependent K+-stimulated cotransporter that is pH sensitive and electrogenic. A second Na+-dependent transporter could not be discriminated, and there was no observable Na+-independent uptake. An outwardly directed K+ gradient (100 mM KCl inside) resulted in a 5- to 10-fold stimulation in glutamate uptake in the presence of Na+. Intravesicular KCl had no effect on transporter affinity but increased transporter velocity in a concentration-dependent manner. Inhibition of Na+-K+-dependent uptake of L-aspartate and L-glutamate (20 mM, 30 s) by 2 mM unlabeled amino acids demonstrated stereoselectivity for L-glutamate but not for L-aspartate. The neutral amino acids (L-alanine, L-threonine, L-serine, L-cysteine, L-phenylalanine) were not effective inhibitors. These data are consistent with an anionic amino acid transporter in the microvillous membrane of the trophoblast, which has characteristics qualitatively similar to the X-AG system found in other epithelia. This system may mediate the concentrative placental uptake of anionic amino acids from maternal blood in utero.

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Placental amino acid uptake. VI. Regulation by intracellular substrate

AJP Cell Physiology ◽

10.1152/ajpcell.1982.243.1.c46 ◽

1982 ◽

Vol 243 (1) ◽

pp. C46-C51 ◽

Cited By ~ 9

Author(s):

R. B. Steel ◽

C. H. Smith ◽

L. K. Kelley

Keyword(s):

Amino Acid ◽

Placental Tissue ◽

Membrane Vesicles ◽

Amino Acid Uptake ◽

Maternal Plasma ◽

Acid Uptake ◽

L System ◽

Intracellular Amino Acids ◽

Human Placental Tissue

Amino acid uptake by human placental tissue is regulated by intracellular amino acids. alpha-Aminoisobutyric acid (AIB) uptake was reduced at intracellular AIB concentrations of 0.8 mM. The magnitude of reduction increased sharply between 1 and 3 mM and reached a maximum of 45% at 5 mM. Suppression was specific to the "A" system. It occurred only when both the amino acid used for preloading and that used as an uptake substrate were active with that system. In the "L" system, facilitation apparently occurs, and in the "ASC" system there is no apparent effect. The system specificity as well as other evidence indicated that suppression is caused by substrate present intracellularly rather than by dilution of extracellular substrate. Suppression was independent of inhibitors of protein synthesis and was not seen in membrane vesicles prepared from preloaded tissue, indicating that intracellular substrate interacts directly with the carrier (transinhibition) rather than altering its synthesis or degradation. The A system transinhibition has the potential to regulate syncytial uptake in vivo and limit variation due to changes in maternal plasma amino acid concentration.

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