Ion Effects on the H^+-Translocating Adenosine Triphosphatase and Pyrophosphatase Associated with the Tonoplast of Chara corallina

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H^+-translocating ATPase and pyrophosphatase (PPase) associated with the tonoplast of Chara corallina were isolated with the aid of a perfusion technique, and the effects of ions on their activities were studied. All the alkali metal cations tested stimulated the ATPase and ATPdependent H^+ pumping activities only by 10 to 40%・ Anions, on the other hand, strongly affected the activities. Potassium salts of Cl^- and Br^- stimulated them, while F^- and NO_3^- inhibited them. By contrast, the H^+-translocating PPase was insensitive to anions but sensitive to cations. The order of cation stimulation was Rb+=K^+>Cs+>Na^+=Li^+>choline^+. NO_3^- (50 mM), thought to be a specific inhibitor of the tonoplast-type H^+-ATPase, inhibited the ATPdependent H^+ pumping almost completely but the ATPase activity by only about 50%. Na^+ inhibited the PP_i-dependent H^+ pumping (I_<50&t;=50 mM) in the presence of 50 mM KCl but not the ATPdependent one. The PPase was more sensitive to F^- (I_<50>=400 μM) than the ATPase. Both the H^+-ATPase and the H^+-ppase required Mg^<2+> for their activities, although an excess was inhibitory to both. The different sensitivities of the PP_i-dependent and the ATP-dependent H^+- pumping enzymes to ions correspond to the tonoplast enzymes of higher plants and may be used as "markers" to distinguish between these enzymes in characean cells.
日本植物生理学会の論文