Na+ transport via Na+/H+ antiport in Halobacterium halobium envelope vesicles.

Using H. halobium cell envelope vesicles containing either bacteriorhodopsin plus Na+ pump, bacteriorhodopsin alone, Na+ pump alone, or no light-responsive pigment altogether, it could be shown that the large majority of light energized Na+ extrusion in these mutants is linked to bacteriorhodopsin and to protonmotive force, and therefore must be facilitated by a Na+/H+ antiporter. Thus, the recently discovered primary Na+ pump makes only a minor contribution to light-mediated Na+ flux. The activity of the Na+/H+ antiporter appears to be independent of the presence of any photoreactive pigments, since an artifical electron donor will drive rapid Na+ extrusion in all of the vesicle preparations tested.