1. Mrp-dependent Na(+)/H(+) antiporters of Bacillus exhibit characteristics that are unanticipated for completely secondary active transporters.
- Author
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Ito M, Guffanti AA, and Krulwich TA
- Subjects
- Acridine Orange pharmacology, Biological Transport, Biological Transport, Active, Cloning, Molecular, Coloring Agents pharmacology, Dose-Response Relationship, Drug, Electron Transport, Escherichia coli metabolism, Hydrogen-Ion Concentration, Multidrug Resistance-Associated Proteins, Sodium Chloride pharmacology, Sodium-Hydrogen Exchangers metabolism, ATP-Binding Cassette Transporters metabolism, Bacillus metabolism, Escherichia coli Proteins, Hydrogen metabolism, Sodium metabolism
- Abstract
The Na(+)/H(+) antiport activity encoded by the seven-gene mrp operons of Bacillus subtilis and alkaliphilic Bacillus pseudofirmus OF4 were cloned into a low copy plasmid, were expressed in several Escherichia coli mutant strains and compared side-by-side with similarly cloned nhaA, a major secondary antiporter from E. coli. All three antiporter systems exhibited electron donor-dependent antiport in a fluorescence-based vesicle assay, with NhaA being the most active. In whole cells of the same antiporter-deficient strain from which the vesicles were made, E. coli KNabc, Mrp-mediated Na(+) exclusion was significantly more protonophore-resistant than that conferred by NhaA. The Mrp systems were also more efficacious than NhaA: in supporting anaerobic Na(+) resistance in wild type and a terminal oxidase mutant strain of E. coli (SBS2115); and in increasing non-fermentative growth of an NADH dehydrogenase-minus E. coli mutant (ANN0222). The results suggest the possibility that the Mrp systems may have both secondary and primary energization capacities.
- Published
- 2001
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