Sodium-dependent amino acid transport in reconstituted membrane vesicles from Ehrlich ascites cell plasma membranes.
Plasma membranes, isolated from Ehrlich ascites tumor cells, were dissolved in 2% cholate, 4 M urea and then reformed into liposomes upon dialysis at 4 degrees with exogenous phospholipids. Reconstituted vesicles regain the ability to transport amino acids. Na+ was shown to accelerate the uptake of alpha-aminoisobutyrate, phenylalanine, and methionine, but not leucine or epsilon-aminohexanoic acid. With the reconstituted vesicles, methionine, but not leucine, inhibited the uptake of alpha-aminoisobutyrate. An apparent Km value for alpha-aminoisobutyrate uptake of 3.0 mM was obtained. This value is close to that observed with the intact cells and the native membrane vesicles. A Na+ gradient (high Na+ outside) increased alpha-aminoisobutyrate uptake, whereas a reversed gradient (high Na+ inside) increased alpha-aminoisobutyrate efflux. The latter flux was increased by valinomycin, suggesting electrogenic transport. A modest extent of coupling between a Na+ gradient and uphill flow of alpha-aminoisobutyrate was observed.
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D005614:Freeze Fracturing; D007700:Kinetics; D010743:Phospholipids / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*
D000596:Amino Acids; D010743:Phospholipids; D012964:Sodium