Na+(Li+)/Branched-chain amino acid cotransport inPseudomonas aeruginosa

Summary A transport system for branched-chain amino acids (designated as LIV-II system) inPseudomonas aeruginosa requires Na⁺ for its operation. Coupling cation for this system was identified by measuring cation movement during substrate entry using cation-selective electrodes. Uptakes of Na⁺ and Li^– were induced by the imposition of an inwardly-directed concentration gradient of leucine, isoleucine, or valine. No uptake of H^– was found, however, under the same conditions. In addition, effects of Na⁺ and Li⁺ on the kinetic property of the system were examined. At chloride salt concentration of 2.5mm, values of apparentK _m andV _max for leucine uptake were larger in the presence of Na⁺ than Li⁺. These results indicate that the LIV-II transport system is a Na⁺(Li⁺)/substrate cotransport system, although effects of Na⁺ and Li⁺ on kinetics of the system are different.