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A novel antiporter activity catalyzing sodium and potassium transport from right‐side‐out vesicles of E. coli
Author(s) -
Verkhovskaya Marina L.,
Verkhovsky Michael I.,
Wikström Mårten
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)00281-d
Subject(s) - antiporter , vesicle , chemistry , potassium , sodium , biophysics , biochemistry , membrane , biology , organic chemistry
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 + / n H + 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 + / n H + antiporter previously described, and the other is a novel Na + ,K + / m H + antiporter.