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Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
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Related Experiment Video

Updated: May 5, 2026

Separation of Spinach Thylakoid Protein Complexes by Native Green Gel Electrophoresis and Band Characterization using Time-Correlated Single Photon Counting
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Flash-induced redox changes in oxygen-evolving spinach Photosystem II core particles.

P J van Leeuwen1, C Heimann, P Gast

  • 1Department of Biophysics, Huygens Laboratory of the State University, P.O. Box 9504, 2300 RA, Leiden, The Netherlands.

Photosynthesis Research
|December 10, 2013
PubMed
Summary

Investigating flash-induced redox reactions in spinach Photosystem II (PS II) core particles revealed rapid S-state cycling and unusually fast deactivation of higher S-states. Tyrosine D oxidation kinetics were also determined.

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Area of Science:

  • Biochemistry
  • Photosynthesis research
  • Spectroscopy

Background:

  • Photosystem II (PS II) is crucial for oxygenic photosynthesis.
  • Understanding the S-state cycle and redox reactions within PS II is key to elucidating its mechanism.
  • Previous studies on PS II membranes provide a basis for comparison.

Purpose of the Study:

  • To investigate flash-induced redox reactions in spinach PS II core particles.
  • To characterize the kinetics of S-state transitions and tyrosine D oxidation.
  • To compare findings with those from PS II membrane fragments.

Main Methods:

  • Absorbance difference spectroscopy in the UV-region.
  • Electron Paramagnetic Resonance (EPR) spectroscopy.
  • Utilized flash-induced redox reactions with and without artificial electron acceptors.

Main Results:

  • Period-four oscillations in UV absorbance linked to S-state cycle were restored by electron acceptors, but period-two oscillations were not.
  • All active centers were in state S1 after dark adaptation, unlike in PS II membranes.
  • S-state transition kinetics (Z(+)S1→ZS2, Z(+)S2→ZS3, Z(+)S3→ZS0) and Z(+)S0→ZS1 transition were characterized.
  • Deactivation of higher S-states and oxidation of S0 to S1 occurred rapidly (seconds to minutes).
  • Tyrosine D(+) exhibited similar fast kinetics, appearing in inactive and active centers.

Conclusions:

  • Spinach PS II core particles exhibit distinct S-state cycling behavior compared to PS II membranes.
  • The kinetics of S-state transitions and tyrosine D oxidation are rapid in PS II core particles.
  • Electron transport limitations and the role of electron acceptors influence PS II redox dynamics.