Sodium-stimulated amino acid uptake into isolated membrane vesicles from Balb/c 3T3 cells transformed by simian virus 40.

Abstract

Mediated uptake of amino acids by membrane vesicles isolated from Balb/c 3T3 [mouse fibroblast] cells transformed by SV 40 was demonstrated. Initial rates of transport of radioactively labeled L-leucine and .alpha.-aminoisobutyric acid were enhanced by the addition of NaCl (100 mM) to the reaction mixture at the start of the uptake process. This enhancement included a prominent overshoot during initial uptake. Slight stimulation of .alpha.-aminoisobutyric acid uptake was seen with K+, but none with Li+. The mediated nature of the uptake event for L-leucine was shown by saturation kinetics and inhibition with L-valine. The transport assay measured intravesicular amino acid uptake rather than binding, as shown by the variation of uptake in response to changes in extravesicular osmolarity. EM confirmed the presence of closed vesicles. Amino acid transport was characterized in an in vitro membrane vesicle system which should prove useful for studies of growth control.