title: A novel antiporter activity catalyzing sodium and potassium transport from right-side-out vesicles of E. coli.
abstract: Downhill sodium efflux from right-side-out E. coli membrane vesicles was found to be stimulated by negative electric potential, as has been reported earlier [Bassilana et al., Biochemistry 23 (1984) 1015-1022], and in agreement with the concept of electrogenic Na+/nH+ antiporters with n > 1. However, sodium efflux was much more accelerated by positive electric potential, indicating the operation of another sodium transport system. delta pH (alkaline inside), created by a pH shift from 8.5 to 6.8 in the medium was found to drive sodium efflux against its concentration gradient, but only when the vesicles had been loaded with both Na+ and K+. Efflux of K+ against the concentration gradient was also observed under these conditions. When the vesicles were loaded separately with sodium tricine or potassium tricine, no K+ efflux and insignificant Na+ efflux were observed. We propose that there are at least two different mechanisms responsible for Na+ efflux in E. coli vesicles. One is the Na+/nH+ antiporter previously described, and the other is a novel Na+,K+/mH+ antiporter.
authors.affiliation: Institute of Biomedical Sciences, Department of Medical Chemistry, University of Helsinki, Finland.
authors.forename: M L
authors.initials: ML
authors.lastname: Verkhovskaya
authors.forename: M I
authors.initials: MI
authors.lastname: Verkhovsky
authors.forename: M
authors.initials: M
authors.lastname: Wikström
mesh_terms: D017920:Antiporters / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D004058:Diffusion; D004926:Escherichia coli / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000378:metabolism; D008564:Membrane Potentials; D009025:Morpholines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D017920:Antiporters; D008081:Liposomes; D009025:Morpholines; D017923:Sodium-Hydrogen Exchangers; D014634:Valinomycin; C008550:morpholinopropane sulfonic acid; D012964:Sodium; D002794:Choline; D011188:Potassium