K-DEPENDENT NA+ TRANSPORT DRIVEN BY RESPIRATION IN ESCHERICHIA-COLI-CELLS AND MEMBRANE-VESICLES()

Respiration-driven Na+ transport from Escherichia coli cells and right -side-out membrane vesicles is strictly dependent on K+. Cells from an E. coli mutant deficient in three major K+ transport systems were inc apable of accumulating K+ or expelling Na+ unless valinomycin was adde d. Membrane vesicles from an E. coli mutant from which the genes encod ing the two known electrogenic Na+/nH(+) antiporters nhaA and nhaB wer e deleted transported Na+ as well as did vesicles from wild-type cells . Quantitative analysis of Delta psi and Delta pH showed a high drivin g force for electrogenic Na+/nH(+) antiport whether K+ was present or not, although Na+ transport occurred only in its presence. These resul ts suggest that an Na+/nH(+) antiporter is not responsible for the Na transport. Respiration-driven efflux of Na+ from vesicles was found t o be accompanied by primary uphill efflux of K+. Also, no respiration- dependent efflux of K+ was observed in the absence of Na+. Such coupli ng between Na+ and K+ fluxes may be explained by the operation of an N a+, K+/H+ antiporter previously described in E. coli membrane vesicles (Verkhovskaya, M.L., Verkhovsky, M.I. and Wikstrom, M. (1995) FEBS Le tt. 363, 46-48). Active Na+ transport is abolished when Delta<(mu)over bar>(H+) is eliminated by a protonophore, but at low concentrations t he protonophore actually accelerated Na+ transport. Such an effect may be expected if the Na+, K+/H+ antiporter normally operates in tight c onjunction with respiratory chain complexes, thus exhibiting some phen omenological properties of a primary redox-linked sodium pump.