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. ΔpH (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. © 1995.
Verkhovskaya, M. L., Verkhovsky, M. I., & Wikström, M. (1995). A novel antiporter activity catalyzing sodium and potassium transport from right-side-out vesicles of E. coli. FEBS Letters, 363(1–2), 46–48. https://doi.org/10.1016/0014-5793(95)00281-D