The relationship between light‐induced increases in the H+ conductivity of thylakoid membranes and activity of the coupling factor

Roger HANGARTER, Doland R. ORT

Research output: Contribution to journalArticle

Abstract

In the absence of a transmembrane electric field, about 15 saturating single‐turnover flashes are required for chloroplast thylakoid membranes to accumulate the 80 mmol H+· mol chlorophyll−1 that are necessary to form a ΔpH sufficiently large to initiate net ATP synthesis. Lowering the number of turnovers of proton‐producing redox components by decreasing the flash intensity increased the number of flashes required for the onset of ATP formation. Thus, regardless of the intensity, the accumulation of the same number of hydrogen ions was needed for phosphorylation to begin. Since the size of the threshold input was constant over a very wide range of proton accumulation rates, it follows that there were no significant proton leakages during the filling of the pool to its threshold level. However, non‐productive leaks were initiated once phosphorylation began since progressively lower phosphorylation efficiencies were observed at lower and lower flash intensities. It is difficult to explain this observation except in terms of competing, non‐phosphorylating hydrogen ion fluxes only when the threshold accumulation had been reached. We observed an increase in the permeability of thylakoid membrane to hydrogen ions that correlated with indications of coupling factor activity: the onset of ATP synthesis, the release of tightly bound ADP and, in dithiothreitol treated membranes, the initiation of ATPase activity. Our data support the notion that the dependence of coupling factor activation and deactivation on the ΔpH accounts for the substantial changes in the ion conductivity that occur in thylakoid membranes.

Original languageEnglish (US)
Pages (from-to)7-12
Number of pages6
JournalEuropean Journal of Biochemistry
Volume158
Issue number1
DOIs
StatePublished - Jul 1986

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Thylakoids
Protons
Phosphorylation
Membranes
Adenosine Triphosphate
Dithiothreitol
Chloroplasts
Adenosine Diphosphate
Oxidation-Reduction
Adenosine Triphosphatases
Permeability
Chemical activation
Electric fields
Ions
Fluxes

ASJC Scopus subject areas

  • Biochemistry

Cite this

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abstract = "In the absence of a transmembrane electric field, about 15 saturating single‐turnover flashes are required for chloroplast thylakoid membranes to accumulate the 80 mmol H+· mol chlorophyll−1 that are necessary to form a ΔpH sufficiently large to initiate net ATP synthesis. Lowering the number of turnovers of proton‐producing redox components by decreasing the flash intensity increased the number of flashes required for the onset of ATP formation. Thus, regardless of the intensity, the accumulation of the same number of hydrogen ions was needed for phosphorylation to begin. Since the size of the threshold input was constant over a very wide range of proton accumulation rates, it follows that there were no significant proton leakages during the filling of the pool to its threshold level. However, non‐productive leaks were initiated once phosphorylation began since progressively lower phosphorylation efficiencies were observed at lower and lower flash intensities. It is difficult to explain this observation except in terms of competing, non‐phosphorylating hydrogen ion fluxes only when the threshold accumulation had been reached. We observed an increase in the permeability of thylakoid membrane to hydrogen ions that correlated with indications of coupling factor activity: the onset of ATP synthesis, the release of tightly bound ADP and, in dithiothreitol treated membranes, the initiation of ATPase activity. Our data support the notion that the dependence of coupling factor activation and deactivation on the ΔpH accounts for the substantial changes in the ion conductivity that occur in thylakoid membranes.",
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