Mechanism of Na+/H+ exchange by Escherichia coli NhaA in reconstituted proteoliposomes

FEBS Letters

Taglicht, D.¹  Dibrov, P.A.¹ 

[1] Division of Microbial and Molecular Ecology, The Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Givat Ram, 91904 Jerusalem, Israel

关键词: Na+/H+ exchange;    Na+/H+ antiporter;    NhaA;    Ion transport;    pH regulation;    Escherichia coli;    ΔμH + and ΔμNa +;    transmembrane differences in electrochemical H+ and Na+ potentials;    respectively;    Δψ;    transmembrane electric potential difference;    ΔpH and ΔpNa;    transmembrane H+ and Na+ concentration gradients;    CCCP;    carbonyl cyanide m-chlorophenylhydrazon;   

DOI  :  10.1016/0014-5793(93)80869-V

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

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 NH₄ 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 ²²Na⁺ 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 ²²Na⁺ suggesting that the translocation of the Na⁺loaded form of the carrier is faster than the rest of the catalytic cycle.

【 授权许可】

Unknown