Sodium-dependent transport of L-leucine in membrane vesicles prepared from Pseudomonas aeruginosa

Publisher Website
Google Scholar
Abstract
Membrane vesicles were prepared by osmotic lysis of spheroplasts of P. aeruginosa strain P14, and the active transport of amino acids was studied. D-Glucose, gluconate and L-malate supported active transport of various L-amino acids. The respiration-dependent leucine transport was markedly stimulated by Na+. Moreover, without any respiratory substrate, leucine was also transported transiently by the addition of Na+ alone. This transient uptake of leucine was not inhibited by carbonyl cyanide p-trifluoromethoxyphenylhydrazone or valinomycin, but was completely abolished by gramicidin D. Increase in the Na+ concentration of the medium resulted in a decrease of the Km for L-leucine transport, but the Vmax was not significantly affected. Active transport of leucine was inhibited competitively by isoleucine or by valine, whose transport was also stimulated by Na+. Na+ was not required for the uptake of other L-amino acids tested, but rather was inhibitory for some of them. A common transport system for branched-chain amino acids exists in membrane vesicles, the system requires Na+ for its activity, and an Na+ gradient can drive the system.