Characterization and reconstitution of the Na+/H+ antiporter from the plasma membrane of the halotolerant alga Dunaliella.

Na+/H+ exchange activity in plasma membrane preparations isolated from the unicellular halotolerant alga, Dunaliella salina, is shown to be competitively inhibited by amiloride or Li+, with Ki values of 25 and 30 microM, respectively. The activity can be followed by either the sodium-dependent change in transvesicular delta pH, as monitored by absorbance changes of Acridine orange, or by the delta pH-dependent uptake of 22Na+ into the intravesicular space. The activity was solubilized, by extraction with Triton, and reconstituted into active proteoliposomes. The activity of the reconstituted proteoliposomes was strongly stimulated by the presence of valinomycin and KCl, suggesting that the exchanger is electrogenic, presumably exchanging more than one proton for each Na+ ion. Partial purification of the Triton-extracted exchanger was obtained by fractionation on a DEAE-cellulose column.