H+‐translocating ATPase and Na+/H+ antiport activities in the plasma membrane of the marine alga Platymonas viridis

Abstract
Proton transport by the vanadate-sensitive ATPase in plasma membrane (PM) vesicles from the marine unicellular microalga Platymonas viridis was investigated. The ATP-dependent generation of ΔpH across the membranes of PM vesicles was followed by the changes in the absorbance of the aminoacridine probe. Acridine orange, Na+ caused the decay of ΔpH generated by the ATPase, the rate of the decay being dependent on the concentrations of Na+ added. The phenomenon was specific for Na+. Amiloride inhibited Na+-dependent ΔpH decay. The experiments support the idea of a Na+-extruding mechanism (H+-translocating ATPase plus Na+/H+ antiporter) operating in the PM of marine alga Pl. viridis