The Na + -translocating ATPase in the plasma membrane of the marine microalga Tetraselmis viridis catalyzes Na + /H + exchange

Abstract

Our previous investigations have established that Na+ translocation across the Tetraselmis viridis plasma membrane (PM) mediated by the primary ATP-driven Na+-pump, Na+-ATPase, is accompanied by H+ counter-transport [Y.V. Balnokin et al. (1999) FEBS Lett 462:402-406]. The hypothesis that the Na+-ATPase of T. viridis operates as an Na+/H+ exchanger is tested in the present work. The study of Na+ and H+ transport in PM vesicles isolated from T. viridis demonstrated that the membrane-permeant anion NO3- caused (i) an increase in ATP-driven Na+ uptake by the vesicles, (ii) an increase in (Na(+)+ATP)-dependent vesicle lumen alkalization resulting from H+ efflux out of the vesicles and (iii) dissipation of electrical potential, deltapsi, generated across the vesicle membrane by the Na+-ATPase. The (Na(+)+ATP)-dependent lumen alkalization was not significantly affected by valinomycin, addition of which in the presence of K+ abolished deltapsi at the vesicle membrane. The fact that the Na+-ATPase-mediated alkalization of the vesicle lumen is sustained in the absence of the transmembrane deltapsi is consistent with a primary role of the Na+-ATPase in driving H+ outside the vesicles. The findings allowed us to conclude that the Na+-ATPase of T. viridis directly performs an exchange of Na+ for H+. Since the Na+-ATPase generates electric potential across the vesicle membrane, the transport stoichiometry is mNa+/nH+, where m> n.

Changes in plasmalemma K+Mg2+-ATPase dephosphorylating activity and H+ transport in relation to seasonal growth and freezing tolerance of Festuca pratensis Huds

“…In this respect, the Na + -ATPase of the plasma membrane of the marine microalgae Tetraselmis viridis directly performs an exchange of Na + for H + , which makes a vital contribution to salt tolerance of algae cells (Balnokin et al, 2004). The activity of the proton pump in cucumber (Cucumis sativus) root plasmalemma, after 1 day of exposure at 8 1C, decreases from 30 to 16 mM P i mg À1 protein h À1 (Lee et al, 2004).…”

“…Investigations into the membrane proton pump mechanism have been conducted by using different parts of the plants: coleoptiles and roots of barley, wheat and maize, cucumber seedlings and, especially, cells of algae (Arango et al, 2003;Balnokin et al, 2004;Lee et al, 2004). The H + transport function ensures maintenance of transmembrane potential and cell homeostasis.…”

Na+-stimulated ATPase of alkaliphilic halotolerant cyanobacterium Aphanothece halophytica translocates Na+ into proteoliposomes via Na+ uniport mechanism

“…In this study, we attempted to elucidate the mechanism of Na + - and H + -transport by Na + -stimulated ATPase reconstituted into liposomes. Two possible mechanisms of Na + -transport can be hypothesized [30]. Mechanism 1 proposes that the Na + -stimulated ATPase operates as a uniporter catalyzing only Na + transport across proteoliposomes, subsequently, H + transport is driven by the membrane potential generated by Na + -stimulated ATPase.…”

“…H + efflux does not occur directly via Na + -stimulated ATPase but is driven by the membrane potential generated during Na + -stimulated ATPase operation. The operation of Na + -stimulated ATPase as a Na + uniporter has been previously reported in the halotolerant microalga Dunaliella maritima [28] while Na + -translocating ATPase in the marine microalga Tetraselmis viridis operates as a Na + /H + exchanger [30]. …”

“…In the halotolerant microalga Dunaliella maritima , it was found that Na + uptake across the plasma membrane by Na + -ATPase is electrogenic [28] and the mechanism of Na + transport by Na + -ATPase is suggested to operate as an Na + uniporter which carries only Na + ions for transport across the plasma membrane while the transport of H + , a counterion, is driven by an electrical membrane potential generated by Na + -ATPase [29]. On the contrary, the mechanism of Na + transport across the plasma membrane of the marine microalga Tetraselmis viridis by Na + -ATPase is suggested to operate as an Na + /H + exchanger which catalyzes an exchange of Na + for H + [30]. In this study, Na + -stimulated ATPase from A. halophytica was purified and reconstituted into liposomes.…”