Photodamage of a Mn(III/IV)-oxo mixed-valence compound and photosystem II: Evidence that a high-valent manganese species is responsible for UV-induced photodamage of the oxygen-evolving complex in photosystem II

Zi Wei, Clyde W. Cady, Gary W Brudvig, Harvey J M Hou

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Abstract

The Mn cluster in photosystem II (PS II) is believed to play an important role in the UV photoinhibition of green plants, but the mechanism is still not clear at a molecular level. In this work, the photochemical stability of [MnIII(O)2MnIV(H2O) 2(Terpy)2](NO3)3 (Terpy = 2,2′:6′,2″-terpyridine), designated as Mn-oxo mixed-valence dimer, a well characterized functional model of the oxygen-evolving complex in PS II, was examined in aqueous solution by exposing the complex to excess light irradiation at six different wavelengths in the range of 250 to 700 nm. The photodamage of the Mn-oxo mixed-valence dimer was confirmed by the decrease of its oxygen-evolution activity measured in the presence of the chemical oxidant oxone. Ultraviolet light irradiation induced a new absorption peak at around 400-440 nm of the Mn-oxo mixed-valence dimer. Visible light did not have the same effect on the Mn-oxo mixed-valence dimer. We speculate that the spectral change may be caused by conversion of the Mn(III)O2Mn(IV) dimer into a new structure - Mn(IV)O2Mn(IV). In the processes, the appearance of a 514 nm fluorescence peak was observed in the solution and may be linked to the hydration or protonation of Terpy ligand in the Mn-oxo dimer. In comparing the response of the PS II functional model compound and the PS II complex to excess light radiation, our results support the idea that UV photoinhibition is triggered at the Mn4Ca center of the oxygen-evolution complex in PS II by forming a modified structure, possibly a Mn(IV) species, and that the reaction of Mn ions is likely the initial step.

Original languageEnglish
Pages (from-to)118-125
Number of pages8
JournalJournal of Photochemistry and Photobiology B: Biology
Volume104
Issue number1-2
DOIs
Publication statusPublished - Jul 2011

Fingerprint

Photosystem II Protein Complex
Manganese
manganese
dimers
Oxygen
valence
oxygen
Viridiplantae
Light
Ultraviolet Rays
irradiation
Oxidants
ultraviolet radiation
Fluorescence
hydration
Ions
Radiation
Ligands
aqueous solutions
fluorescence

Keywords

  • Manganese-oxo compound
  • Oxygen evolution
  • Photodamage
  • Photoinhibition
  • PS II
  • UV effect

ASJC Scopus subject areas

  • Radiation
  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology
  • Biophysics

Cite this

@article{186cd65f2482419a94f05789ce26dd52,
title = "Photodamage of a Mn(III/IV)-oxo mixed-valence compound and photosystem II: Evidence that a high-valent manganese species is responsible for UV-induced photodamage of the oxygen-evolving complex in photosystem II",
abstract = "The Mn cluster in photosystem II (PS II) is believed to play an important role in the UV photoinhibition of green plants, but the mechanism is still not clear at a molecular level. In this work, the photochemical stability of [MnIII(O)2MnIV(H2O) 2(Terpy)2](NO3)3 (Terpy = 2,2′:6′,2″-terpyridine), designated as Mn-oxo mixed-valence dimer, a well characterized functional model of the oxygen-evolving complex in PS II, was examined in aqueous solution by exposing the complex to excess light irradiation at six different wavelengths in the range of 250 to 700 nm. The photodamage of the Mn-oxo mixed-valence dimer was confirmed by the decrease of its oxygen-evolution activity measured in the presence of the chemical oxidant oxone. Ultraviolet light irradiation induced a new absorption peak at around 400-440 nm of the Mn-oxo mixed-valence dimer. Visible light did not have the same effect on the Mn-oxo mixed-valence dimer. We speculate that the spectral change may be caused by conversion of the Mn(III)O2Mn(IV) dimer into a new structure - Mn(IV)O2Mn(IV). In the processes, the appearance of a 514 nm fluorescence peak was observed in the solution and may be linked to the hydration or protonation of Terpy ligand in the Mn-oxo dimer. In comparing the response of the PS II functional model compound and the PS II complex to excess light radiation, our results support the idea that UV photoinhibition is triggered at the Mn4Ca center of the oxygen-evolution complex in PS II by forming a modified structure, possibly a Mn(IV) species, and that the reaction of Mn ions is likely the initial step.",
keywords = "Manganese-oxo compound, Oxygen evolution, Photodamage, Photoinhibition, PS II, UV effect",
author = "Zi Wei and Cady, {Clyde W.} and Brudvig, {Gary W} and Hou, {Harvey J M}",
year = "2011",
month = "7",
doi = "10.1016/j.jphotobiol.2011.01.017",
language = "English",
volume = "104",
pages = "118--125",
journal = "Journal of Photochemistry and Photobiology B: Biology",
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TY - JOUR

T1 - Photodamage of a Mn(III/IV)-oxo mixed-valence compound and photosystem II

T2 - Evidence that a high-valent manganese species is responsible for UV-induced photodamage of the oxygen-evolving complex in photosystem II

AU - Wei, Zi

AU - Cady, Clyde W.

AU - Brudvig, Gary W

AU - Hou, Harvey J M

PY - 2011/7

Y1 - 2011/7

N2 - The Mn cluster in photosystem II (PS II) is believed to play an important role in the UV photoinhibition of green plants, but the mechanism is still not clear at a molecular level. In this work, the photochemical stability of [MnIII(O)2MnIV(H2O) 2(Terpy)2](NO3)3 (Terpy = 2,2′:6′,2″-terpyridine), designated as Mn-oxo mixed-valence dimer, a well characterized functional model of the oxygen-evolving complex in PS II, was examined in aqueous solution by exposing the complex to excess light irradiation at six different wavelengths in the range of 250 to 700 nm. The photodamage of the Mn-oxo mixed-valence dimer was confirmed by the decrease of its oxygen-evolution activity measured in the presence of the chemical oxidant oxone. Ultraviolet light irradiation induced a new absorption peak at around 400-440 nm of the Mn-oxo mixed-valence dimer. Visible light did not have the same effect on the Mn-oxo mixed-valence dimer. We speculate that the spectral change may be caused by conversion of the Mn(III)O2Mn(IV) dimer into a new structure - Mn(IV)O2Mn(IV). In the processes, the appearance of a 514 nm fluorescence peak was observed in the solution and may be linked to the hydration or protonation of Terpy ligand in the Mn-oxo dimer. In comparing the response of the PS II functional model compound and the PS II complex to excess light radiation, our results support the idea that UV photoinhibition is triggered at the Mn4Ca center of the oxygen-evolution complex in PS II by forming a modified structure, possibly a Mn(IV) species, and that the reaction of Mn ions is likely the initial step.

AB - The Mn cluster in photosystem II (PS II) is believed to play an important role in the UV photoinhibition of green plants, but the mechanism is still not clear at a molecular level. In this work, the photochemical stability of [MnIII(O)2MnIV(H2O) 2(Terpy)2](NO3)3 (Terpy = 2,2′:6′,2″-terpyridine), designated as Mn-oxo mixed-valence dimer, a well characterized functional model of the oxygen-evolving complex in PS II, was examined in aqueous solution by exposing the complex to excess light irradiation at six different wavelengths in the range of 250 to 700 nm. The photodamage of the Mn-oxo mixed-valence dimer was confirmed by the decrease of its oxygen-evolution activity measured in the presence of the chemical oxidant oxone. Ultraviolet light irradiation induced a new absorption peak at around 400-440 nm of the Mn-oxo mixed-valence dimer. Visible light did not have the same effect on the Mn-oxo mixed-valence dimer. We speculate that the spectral change may be caused by conversion of the Mn(III)O2Mn(IV) dimer into a new structure - Mn(IV)O2Mn(IV). In the processes, the appearance of a 514 nm fluorescence peak was observed in the solution and may be linked to the hydration or protonation of Terpy ligand in the Mn-oxo dimer. In comparing the response of the PS II functional model compound and the PS II complex to excess light radiation, our results support the idea that UV photoinhibition is triggered at the Mn4Ca center of the oxygen-evolution complex in PS II by forming a modified structure, possibly a Mn(IV) species, and that the reaction of Mn ions is likely the initial step.

KW - Manganese-oxo compound

KW - Oxygen evolution

KW - Photodamage

KW - Photoinhibition

KW - PS II

KW - UV effect

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