Concentration Gradient Effects of Sodium and Lithium Ions and Deuterium Isotope Effects on the Activities of H-ATP Synthase from Chloroplasts

We explored the concentration gradient effects of the sodium and lithium ions and the deuterium isotope's effects on the activities of H⁺-ATP synthase from chloroplasts (CF₀F₁). We found that the sodium concentration gradient can drive the ATP synthesis reaction of CF₀F₁. In contrast, the lithium ion can be an efficient enzyme-inhibitor by blocking the entrance channel of the ion translocation pathway in CF₀. In the presence of sodium or lithium ions and with the application of a membrane potential, unexpected enzyme behaviors of CF₀F₁ were evident. To account for these observations, we propose that both of the sodium and lithium ions could undergo localized hydrolysis reactions in the chemical environment of the ion channel of CF₀. The protons generated locally could proceed to complete the ion translocation process in the ATP synthesis reaction of CF₀F₁. Experimental and theoretical deuterium isotope effects of the localized hydrolysis on the activities of CF₀F₁, and the energetics of these related reactions, support this proposed mechanism. Our experimental observations could be understood in the framework of the well-established ion translocation models for the H⁺-ATP synthase from Escherichia coli, and the Na⁺-ATP synthase from Propionigenium modestum and Ilyobacter tartaricus.