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Mechanism of Na + /H + exchange by Escherichia coli NhaA in reconstituted proteoliposomes
Author(s) -
Dibrov P.A.,
Taglicht D.
Publication year - 1993
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(93)80869-v
Subject(s) - antiporter , chemistry , sodium , escherichia coli , ion exchange , vesicle , sodium–hydrogen antiporter , antiporters , ion , efflux , biophysics , membrane , chromatography , biochemistry , organic chemistry , biology , gene
Purified NhaA, a Na + /H + antiporter from Escherichia coli , reconstituted into proteoliposomes was used to study partial reactions catalyzed by this protein. Homologous Na + /Na + exchange as well as Na + /Li + exchange via NhaA were detected by monitoring the effects of external Li + and Na + ions on the ΔpH‐driven sodium uptake into NH 4 Cl‐loaded vesicles. Furthermore, a sodium counterflow reaction was demonstrated in proteoliposomes preloaded with non‐radioactive Na + and placed into the experimental buffer containing low amounts of 22 Na + under experimental conditions when both components of protonmotive force generated by the antiporter. ΔΨ and ΔpH, were dissipated by corresponding ionophores. The apparent K m for sodium counterflow is 1.1 mM, and V max is 80 of protein. External Na + accelerates the downhill efflux of 22 Na + suggesting that the translocation of the Na + loaded form of the carrier is faster than the rest of the catalytic cycle.