PRESENCE OF A SODIUM-TRANSLOCATING ATPASE IN MEMBRANE-VESICLES OF THE HOMOACETOGENIC BACTERIUM ACETOBACTERIUM-WOODII

Inverted membrane vesicles of the homoacetogenic bacterium Acetobacterium woodii catalyzed the hydrolysis of ATP with a rate of 100-150 nmol . min-1 . mg protein-1. The ATPase was stimulated 1.4-1.6-fold by NaCl and inhibited by N,N'-dicyclohexylcarbodiimide, tributyltin or azide. The degree of inhibition caused by F0-directed but not F1-directed inhibitors was affected by the Na+ concentration in the medium. These experiments indicated the presence of a sodium-translocating ATPase. This was verified by transport studies. Upon addition of ATP to inverted vesicles, Na-22(+) was actively transported into the intravesicular space up to a 24-fold accumulation. Na+ transport was inhibited by the sodium ionophore N,N,N'N',-tetracyclohexyl-1,2-phenylenedioxydiacetamide but stimulated by valinomycin with potassium whereas the protonophore 3,5-di-tert-butyl-4-hydroxybenzylidenemalonitrile was without effect. N,N'dicyclohexylcarbodiimide and tributyltin inhibited Na-22(+) transport. These experiments are in accordance with a primary electrogenic Na+ transport as catalyzed by a F1F0-ATPase.