title: Generation of reactive oxygen species upon strong visible light irradiation of isolated phycobilisomes from Synechocystis PCC 6803.
abstract: The mechanism of photodegradation of antenna system in cyanobacteria was investigated using spin trapping ESR spectroscopy, SDS-PAGE and HPLC-MS. Exposure of isolated intact phycobilisomes to illumination with strong white light (3500 micromol m(-2) s(-1) photosynthetically active radiation) gave rise to the formation of free radicals, which subsequently led to specific protein degradation as a consequence of reactive oxygen species-induced cleavage of the polypeptide backbone. The use of specific scavengers demonstrated an initial formation of both singlet oxygen (1O2) and superoxide (O2(-)), most likely after direct reaction of molecular oxygen with the triplet state of phycobiliproteins, generated from intersystem crossing of the excited singlet state. In a second phase carbon-based radicals, detected through the appearance of DMPO-R adducts, were produced either via O2(-) or by direct 1O2 attack on amino acid moieties. Thus photo-induced degradation of intact phycobilisomes in cyanobacteria occurs through a complex process with two independent routes leading to protein damage: one involving superoxide and the other singlet oxygen. This is in contrast to the mechanism found in plants, where damage to the light-harvesting complex proteins has been shown to be mediated entirely by 1O2 generation.
authors: Department of Environmental Sciences, University of Tuscia, Viterbo, Italy.
authors: Sara
authors: S
authors: Rinalducci
authors: Jens Z
authors: JZ
authors: Pedersen
authors: Lello
authors: L
authors: Zolla
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D013058:Mass Spectrometry; D045524:Phycobilisomes / Q000378:metabolism / Q000528:radiation effects*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D026082:Singlet Oxygen / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D046939:Synechocystis / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D045524:Phycobilisomes; D017382:Reactive Oxygen Species; D013481:Superoxides; D026082:Singlet Oxygen