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Correlation between membrane-localized protons and flash-driven ATP formation in chloroplast thylakoids
Journal of Bioenergetics and Biomembranes
|June 1, 1984
Summary
Protonated amine groups in spinach chloroplasts are essential for efficient ATP formation. Deprotonating these groups delays ATP synthesis, but reprotonation restores normal function, highlighting their role in energy coupling.
Area of Science:
- Plant Physiology
- Bioenergetics
- Photosynthesis Research
Background:
- Adenosine triphosphate (ATP) formation in chloroplasts is driven by proton gradients across thylakoid membranes.
- Membrane-bound amine buffering pools play a role in regulating proton concentration during photophosphorylation.
- The precise mechanism and location of amine buffering in proton coupling remain under investigation.
Purpose of the Study:
- To investigate the role of the protonated state of membrane protein amine buffering pools in flash-induced ATP synthesis in spinach thylakoids.
- To determine the impact of deprotonation and reprotonation of these pools on the kinetics of ATP formation.
- To explore the potential localization of amine buffering within membrane protein structures.
Main Methods:
- Utilized spinach thylakoids and a luciferin luminescence assay to measure ATP formation kinetics under single turnover flashes.
- Manipulated the protonation state of membrane amine pools using specific conditions and the uncoupler desaspidin.
- Assessed ATP formation onset lag under protonated, deprotonated, and reprotonated states of the amine buffering pool.
Main Results:
- Deprotonation of the amine buffering pool delayed the onset of ATP formation by approximately 10 flashes.
- Reprotonation of the deprotonated pool restored the initial ATP formation kinetics, reducing the delay significantly.
- The size of the proton released by flashes matched the capacity of the amine buffering pool, supporting its involvement.
Conclusions:
- The protonated state of amine buffering groups is critical for efficient proton flow to the coupling complex and subsequent ATP synthesis.
- These buffering groups are likely sequestered within membrane proteins, facilitating localized proton transfer.
- The findings support a model where localized proton buffering sites within membrane proteins are essential for photophosphorylation.