THE ATP-DRIVEN NA-PUMP IN THE PLASMA-MEMBRANE OF THE MARINE UNICELLULAR ALGA, PLATYMONAS-VIRIDIS()

The ATP-supported (22)NA(+) uptake by plasma membrane vesicles from th e marine microalga, Platymonas viridis, was studied. At pH 7 in the me dium, Na+ uptake did not occur in the presence of ATP although Delta p H across the plasma membrane was generated. The ATP-dependent Na+ upta ke was induced by adding the protonophore, CICCP. At pH 8, Na+ uptake took place when ATP was added even without CICCP. The Delta pH generat ed across the plasma membrane was negligible under these conditions. T he Na+ uptake at pH 8 was not affected by C1CCP and amiloride, an inhi bitor of the Na+/H+ antiporter. It is concluded that the ATP-supported Na+ uptake by PI. viridis vesicles is catalyzed by Na+-ATPase.