Na super(+)-transporting ATPase in the plasma membrane of halotolerant microalga Dunaliella maritima operates as a Na super(+) uniporter

• Published in: Russian journal of plant physiology Vol. 53; no. 4; pp. 474 - 480
• Main Authors: Popova, L G, Kornilova, A G, Shumkova, G A, Andreev, I M, Balnokin, YuV
• Format: Journal Article
• Language: English
• Published: 01.07.2006
• Subjects: Dunaliella
• ISSN: 1021-4437; 1608-3407
• DOI: 10.1134/S1021443706040078

A fraction of inside-out membrane vesicles enriched in plasma membranes (PM) was isolated from Dunaliella maritima cells. Attempts were made to reveal ATP-driven Na super(+)-dependent H super(+) efflux from the PM vesicles to external medium, as detected by alkalization of the vesicle lumen. In parallel experiments, ATP-dependent Na super(+) uptake and electric potential generation in PM vesicles were investigated. The alkalization of the vesicle lumen was monitored with an impermeant pH-sensitive optical probe pyranine (8-hydroxy-1,3,6-pyrenetrisulfonic acid), which was loaded into vesicles during the isolation procedure. Sodium uptake was measured with super(22)Na super(+) radioactive label. The generation of electric potential in PM vesicles (positive inside) was recorded with a voltage-sensitive probe oxonol VI. Appreciable Na super(+)-and ATP-dependent alkalization of vesicle lumen was only observed in the presence of a protonophore CCCP (carbonyl cyanide-chlorophenylhydrazone). In parallel experiments, CCCP accelerated the ATP-dependent super(22)Na super(+) uptake and abolished the electric potential generated by the Na super(+)-ATPase at the vesicle membrane. A permeant anion NO super(-) sub(3) accelerated ATP-dependent super(22)Na super(+) uptake and promoted dissipation of the electric potential like CCCP did. At the same time, NO super(-) sub(3) inhibited the ATP-and Na super(+)-dependent alkalization of the vesicle lumen. The results clearly show that the ATP-and Na super(+)-dependent H super(+) efflux from PM vesicles of D. maritima is driven by the electric potential generated at the vesicle membrane by the Na super(+)-ATPase. Hence, the Na super(+)-transporting ATPase of D. maritima carries only one ion species, i.e., Na super(+). Proton is not involved as a counter-ion in the catalytic cycle of this enzyme.