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During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...
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Related Experiment Video

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High efficient cyclic electron flow and functional supercomplexes in Chlamydomonas cells.

Pierre Joliot1, Julien Sellés1, Françis-André Wollman1

  • 1Laboratoire de Biologie du Chloroplaste et Perception de la Lumière Chez les Microalgues, Institut de Biologie Physico-Chimique, CNRS UMR 7141, Sorbonne Université, Paris, France.

Biochimica Et Biophysica Acta. Bioenergetics
|August 11, 2022
PubMed
Summary
This summary is machine-generated.

Cyclic electron flow (CEF) around Photosystem I (PSI) in Chlamydomonas reinhardtii is highly efficient, facilitated by a supercomplex involving PSI, cytochrome b6f, and plastocyanin (PC). This supercomplex formation requires a kinase-driven transition to state 2.

Keywords:
Cyclic electron transferCytochrome b(6)fMethyl viologenPSISupercomplex

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Area of Science:

  • Photosynthesis research
  • Plant molecular biology
  • Biochemistry

Background:

  • Cyclic electron flow (CEF) around Photosystem I (PSI) is crucial for ATP production in photosynthesis.
  • Understanding the regulation and efficiency of CEF is key to optimizing photosynthetic processes.

Purpose of the Study:

  • To investigate the mechanism and regulation of high-rate CEF in Chlamydomonas reinhardtii.
  • To identify the molecular components and conditions facilitating efficient CEF.

Main Methods:

  • Measurement of CEF rates in intact Chlamydomonas cells under anaerobic conditions.
  • Analysis of P700 and plastocyanin (PC) absorbance changes.
  • Study of CEF in mutants defective in state transitions.

Main Results:

  • A very high CEF rate (~180-210 s⁻¹) was measured in the presence of methyl viologen (MV).
  • A functional supercomplex of 2 PC, 1 PSI, and 1 cytochrome b6f (cytb6f) is proposed to be responsible for high CEF rates.
  • Supercomplex formation requires a kinase-driven transition to state 2, but not LHCII antenna movement.
  • MV facilitates electron transfer from PSI acceptors to the stromal side of cytb6f.

Conclusions:

  • A PSI-cytb6f-PC supercomplex configuration underlies efficient CEF in Chlamydomonas.
  • State 2 transition, regulated by STT7 kinase and potentially involving PETO protein, is essential for supercomplex formation.
  • Methyl viologen enhances CEF by mediating electron transfer, while supercomplex formation is an intrinsic regulatory mechanism.