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Calcium transport mediated by NhaA, a Na + /H + antiporter from Escherichia coli
Author(s) -
Dibrov P.A.
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)80870-z
Subject(s) - antiporter , chemistry , vesicle , calcium , biophysics , ion transporter , membrane , membrane potential , biochemistry , biology , organic chemistry
In everted membrane vesicles of E. coli strain EP432/pGM42, which has only one Na + /H + antiporter (NhaA), external CaC4 inhibits dissipation of the respiration‐dependent ΔpH in response to the addition of NaCl at pH 7.5, and decreases equilibrium concentration of the intravesicular Na + . In the NhaA proteoliposomes, imposition of an artificial ΔpH (acid inside) leads to the several‐fold accumulation of calcium. The apparent K m for this ΔpH‐driven Ca 2+ uptake at pH 8.5 is 2 mM, and the V max is 1.79 of protein. Dissipation of ΔpH causes release of calcium from the vesicles. CaCl 2 was found to inhibit the ΔpH‐driven Na + uptake mediated by reconstituted NhaA, and vice versa. Further, heterological Ca 2+ /Na + exchange has been demonstrated in proteoliposomes containing NhaA. Transmembrane electric potential difference proved to drive this process. All these data are consistent with the assumption that NhaA can also catalyze Ca 2+ /H + exchange.