Relationship between the Na+/H+ antiporter and Na+/substrate symport in Bacillus alcalophilus.
- 1 March 1981
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 78 (3), 1481-1484
- https://doi.org/10.1073/pnas.78.3.1481
Abstract
The Na+/H+ antiporter of the obligate alkalophile B. alcalophilus facilitates growth at alkaline pH and precludes growth below pH 8.5. Thus, nonalkalophilic mutant strains do not exhibit Na+/H+ antiport activity and, interestingly, such strains concomitantly lose the ability to catalyze Na+-dependent accumulation of .alpha.-aminoisobutyrate. Several other Na+-dependent transport systems are now documented in vesicles from the wild-type strain and it is demonstrated that these systems are defective in vesicles from the nonalkalophilic mutant KM23. Surprisingly, the defect seems to result not from the loss of Na+/H+ antiport activity per se, but from a pleiotropic defect in the Na+/substrate symporters themselves. Monensin, an ionophore that catalyzes Na+/H+ exchange, does not restore respiration-driven Na+/substrate symport in KM23 vesicles. With KM23 vesicles, efflux of .alpha.-aminoisobutyrate, L-malate and L-aspartate down their respective concentration gradients is not stimulated by Na+, in contrast to the observations with wild-type vesicles. Because monensin should ameliorate a simple defect in Na+/H+ antiport activity and the antiporter should not be required for Na+/substrate symport down a concentration gradient, the results suggest that there may be a direct relationship between the antiporter and various Na+/substrate symporters. One possibility is that the systems share a Na+-translocating subunit.This publication has 30 references indexed in Scilit:
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