Rapid-Scan Time-Resolved ATR-FTIR Study on the Photoassembly of the Water-Oxidizing Mn4CaO5Cluster in Photosystem II

Akihiko Sato, Yuki Nakano, Shin Nakamura, Takumi Noguchi

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1 Citation (Scopus)


The catalytic center of photosynthetic water oxidation, the Mn4CaO5 cluster, is assembled in photosystem II (PSII) through a light-driven process called photoactivation, whose mechanism remains elusive. Here, we used rapid-scan time-resolved Fourier transform infrared (FTIR) spectroscopy combined with the attenuated total reflection (ATR) technique to monitor the photoactivation process. Rapid-scan ATR-FTIR spectra of apo-PSII with Mn2+ upon flash illumination showed spectral features typical of carboxylate stretching vibrations, which were attributed to two carboxylate ligands, D1-D170 and D1-E189, by quantum chemical calculations. The FTIR signal decayed with a time constant of ∼0.7 s, showing that the subsequent "dark rearrangement"step occurred with a low quantum yield and Mn3+ ions were mostly released during this decay. Simulation of the kinetic process provided a slow intrinsic rate of the dark rearrangement, which was attributed to a large protein conformational change. The photoassembly mechanism of the Mn4CaO5 cluster is proposed based on these findings.

Original languageEnglish
Pages (from-to)4031-4045
Number of pages15
JournalJournal of Physical Chemistry B
Issue number16
Publication statusPublished - Apr 29 2021
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry


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