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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

Paper ID Volume ID Publish Year Pages File Format Full-Text
29618 44425 2011 8 PDF Available
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.

Graphical abstractThe effect of UV and visible light on [MnIII(O)2MnIV(H2O)2(Terpy)2](NO3)3 (Terpy = 2,2′:6′,2″-terpyridine) and PS II complexes ware examined at six wavelengths. UV light irradiation caused the formation of a Mn(IV/IV) species, and visible light did not. The results support that UV photoinhibition is triggered at the Mn4Ca center of the oxygen-evolution complex in PS II by forming a Mn(IV) species.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► UV irradiation of a Mn(III,IV)-Terpy complex generates a Mn(IV/IV) species but visible light does not. ► Spectroscopic measurements indicate that UV light causes disproportionation of the Mn complex. ► The results suggest that UV photoinhibition is triggered at the Mn4Ca center of photosystem II.

Keywords
Manganese-oxo compound; UV effect; Oxygen evolution; PS II; Photodamage; Photoinhibition
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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
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 104, Issues 1–2, July–August 2011, Pages 118–125
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us