Formation of singlet oxygen by decomposition of protein hydroperoxide in photosystem II.

Ankush Prasad,Vinay Pathak,Pavel Pospíšil,Rajagopal Subramanyam

doi:10.1371/journal.pone.0181732

Ankush Prasad, Vinay Pathak + Show 2 more

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https://doi.org/10.1371/journal.pone.0181732

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Journal: PloS one	Publication Date: Jul 21, 2017
Citations: 14	License type: CC BY 4.0

Affiliation: Palacký University, Olomouc

Abstract

Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. Protein hydroperoxide is formed by protein oxidation initiated by highly oxidizing chlorophyll cation radical and hydroxyl radical formed by Type I photosensitization reaction. Under highly oxidizing conditions, protein hydroperoxide is oxidized to protein peroxyl radical which either cyclizes to dioxetane or recombines with another protein peroxyl radical to tetroxide. These highly unstable intermediates decompose to triplet carbonyls which transfer energy to O2 forming 1O2. Data presented in this study show for the first time that 1O2 is formed by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex.

Highlights

Photosystem II (PSII), a pigment-protein complex present in the thylakoid membrane, catalyzes the reduction of plastoquinol and oxidation of water [1,2,3]
Detection of superoxide anion and hydroxyl radicals by EPR spintrapping To monitor O2− and HO formation in PSII membranes deprived of Mn4O5Ca complex EPR spintrapping spectroscopy was used
Whether HO formation occurs in the PSII antenna complex, POBN-CH(CH3)OH adduct EPR spectra were measured in light-harvesting complex II (LHCII) complex isolated from PSII membranes deprived of Mn4O5Ca complex

Summary

Introduction

Photosystem II (PSII), a pigment-protein complex present in the thylakoid membrane, catalyzes the reduction of plastoquinol and oxidation of water [1,2,3]. Oxidizing TyrZ and reducing Pheo− equivalents are used for the oxidation of water and the reduction of plastoquinone on the lumenal and stromal side of the thylakoid membrane, respectively.

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