Proton slip in the ATP synthase of Rhodobacter capsulatus: induction, proton conduction, and nucleotide dependence

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• 作者：Boris A. Feniouk ; Armen Y. Mulkidjanian ; Wolfgang Junge
• 关键词：ATP synthase ; Proton slip ; Regulation ; Rhodobacter capsulatus
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2005
• 出版时间：7 January 2005
• 年：2005
• 卷：1706
• 期：1-2
• 页码：184-194
• 全文大小：630 K

文摘

F_OF₁-ATP synthase converts two energetic “currencies” of the cell (ATP and protonmotive force, pmf) by coupling two rotary motors/generators. Their coupling efficiency is usually very high. Uncoupled proton leakage (slip) has only been observed in chloroplast enzyme at unphysiologically low nucleotide concentration.

We investigated the properties of proton slip in chromatophores (sub-bacterial vesicles) from Rhodobacter capsulatus in the single-enzyme-per-vesicle mode. The membrane was energized by excitation with flashing light and the relaxation of the transmembrane voltage and pH difference was photometrically detected. We found that: (1) Proton slip occurred only at low nucleotide concentration (<1 μM) and after pre-illumination over several seconds. (2) Slip induction by pmf was accompanied by the release of ≈0.25 mol ADP per mole of enzyme. There was no detectable detachment of F₁ from F_O. (3) The transmembrane voltage and the pH difference were both efficient in slip induction. Once induced, slip persisted for hours, and was only partially reverted by the addition of ADP or ATP (>1 μM). (4) There was no pmf threshold for the proton transfer through the slipping enzyme; slip could be driven both by voltage and pH difference. (5) The conduction was ohmic and weakly pH-dependent in the range from 5.5 to 9.5. The rate constant of proton transfer under slip conditions was 185 s⁻¹ at pH 8.

Proton slip probably presents the free-wheeling of the central rotary shaft, subunit γ, in an open structure of the (αβ)₃ hexagon with no nucleotides in the catalytic sites.