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

Abstract

A transport system for branched-chain amino acids (designated as LIV-II system) in Pseudomonas 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 2.5 mM, values of apparent Km and Vmax 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.

Microbial Genomics and the Periodic Table

“…In E. coli, lithium detoxification is at least partly mediated by Li ϩ efflux via an Na ϩ /H ϩ antiporter (51). Despite its toxicity, Li ϩ can substitute for Na ϩ in the cotransport of amino acids and some sugars in some bacteria (23,71,122,129,131,132,133). Li ϩ can also replace Na ϩ in driving the flagellar motor of Vibrio alginolyticus (69).…”

Is the protein/lipid hydrophobic matching principle relevant to membrane organization and functions?

“…Interestingly, the amount of decane required to restore optimal (Ca 2+ , Mg 2+ )ATPase activity in the short chain lipids was almost exactly equivalent to increasing the chain length to 20 carbon atoms [37], thus supporting the conclusion that hydrophobic mismatch was responsible for the loss in protein activity. The activities of the human erythrocyte hexose transporter in diCn:1‐PC [43], of the leucine transport system of Lactococcus lactis [44] and Pseudomonas aeruginosa [45] in phosphatidylethanolamine/PC mixtures, of cytochrome c oxidase and the (F1,F0)ATPase complex in diCn:1‐PC [46] were also found to be chain length‐dependent, with maximum activity around 16–18 carbon atoms. MelB affords the first example in which the influences of the protein on the lipids and of the lipids on the protein were analyzed both quantitatively and by reference to the d P and d L parameters (Dumas et al).…”

Secondary solute transport in bacteria

“…Unlike these transporters, the leucine carrier of P. aeruginosa is activated by PE or PG, but not by PC [228]. For the leucine carrier proteins of L. lactis and P. aeruginosa maximal activities have been observed with phospholipids with an acyl chain length of about 18, indicating that also the bilayer thickness is contributing to important lipid-protein interactions [229,230]. Mismatches between the thickness of the hydrophobic a-helices of the membrane proteins and the lipid bilayer are energetically unfavourable (exposure of hydrophobic residues to the water phase).…”