Portal de Periódicos da CAPES

Comparison of ΔpH‐ and Δ φ ‐driven ATP synthesis catalyzed by the H + ‐ATPases from Escherichia coli or chloroplasts reconstituted into liposomes

1999; Wiley; Volume: 457; Issue: 3 Linguagem: Inglês

10.1016/s0014-5793(99)01060-1

1873-3468

Susanne Fischer, Peter Gräber,

Mitochondrial Function and Pathology

The H + ‐ATPases from Escherichia coli , EF 0 F 1 , and from chloroplasts, CF 0 F 1 , were reconstituted in liposomes from phosphatidylcholine/phosphatidic acid. The proteoliposomes were energized by an acid‐base transition and a K + /valinomycin diffusion potential and the initial rate of ATP synthesis was measured as a function of the transmembrane pH difference, ΔpH, and the electric potential difference, Δ φ . With EF 0 F 1 , a rate of 80 s −1 is observed at ΔpH=4.1 and Δ φ ≈140 mV. The rate decreases sigmoidally with Δ φ and at Δ φ ≈0 mV, the rate is about 1 s −1 although ΔpH is still 4.1. Under the same conditions with CF 0 F 1 , a rate of 280 s −1 is observed which decreases to 190 s −1 when Δ φ is abolished, i.e. ATP synthesis catalyzed by EF 0 F 1 and CF 0 F 1 depends in a different way on ΔpH and Δ φ . EF 0 F 1 ‐catalyzed ATP synthesis was measured as a function of ΔpH at a constant Δ φ . The rate depends sigmoidally on ΔpH reaching a maximal rate which cannot be further increased by increasing ΔpH. However, this maximal rate depends on Δ φ , i.e. ΔpH and Δ φ are not kinetically equivalent in driving ATP synthesis. We assume that EF 0 F 1 must be converted into a metastable, active state before it catalyzes proton transport‐coupled ATP synthesis. For EF 0 F 1 , this activation step depends only on Δ φ , whereas for CF 0 F 1 , the activation depends on ΔpH and Δ φ .