Indications for a K+/H+ cotransport system in plasma membranes from two acidophilic microorganisms
1990
Glaser, H.U. | Sekler, I. | Pick, U.
The unicellular green alga Dunalielia acidophila grows optimally at pH 1.0 while maintaining a neutral cytoplasmic pH and a positive membrane potential. To study the mechanism of K+ uptake in this organism and in the acidophilic yeast Metschnikowia reukaufii, 86Rb was trapped in plasma membrane vesicles of these organisms, by freezing and thawing with phospholipid vesicles. Both preparations possess K+-stimulated, vanadate-sensitive H+-ATPases. ATP stimulates 86Rb efflux from the reconstituted vesicles, and the stimulation is abolished by vanadate. The protonophore SF-6847 also inhibits the ATP-dependent 86Rb efflux. In contrast, the lipophilic anion SCN-, which abolishes the ATP-induced membrane potential, does not inhibit 86Rb efflux. An artificial pH difference, acid inside, stimulates 86Rb efflux in reconstituted D. acidophila plasma membranes and the stimulation is not affected by vanadate but is inhibited by SF-6847. These results suggest the existence of a K+/H+ cotransport system acting in parallel to the H+-ATPase in the plasma membranes of these organisms. It can explain how acidophiles accumulate K+ against a large electrochemical potential gradient.
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