The ATP-driven Na +-pump in the plasma membrane of the marine unicellular alga, Platymonas viridis

The ATP-supported 22NA + uptake by plasma membrane vesicles from the marine microalga, Platymonas viridis, was studied. At pH 7 in the medium, Na + uptake did not occur in the presence of ATP although ΔpH across the plasma membrane was generated. The ATP-dependent Na + uptake was induced by adding the protonophore, CICCP. At pH 8, Na + uptake took place when ATP was added even without CICCP. The ΔpH generated across the plasma membrane was negligible under these conditions. The Na + uptake at pH 8 was not affected by CICCP and amiloride, an inhibitor of the Na +/H + antiporter. It is concluded that the ATP-supported Na + uptake by Pl. viridis vesicles is catalyzed by Na +-ATPase.