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Cytochrome b 6 / f Complex as an Indigenous Photodynamic Generator of Singlet Oxygen in Thylakoid Membranes
Author(s) -
Suh HwaJin,
Kim Chang Sook,
Jung Jin
Publication year - 2000
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2000)0710103cbfcaa2.0.co2
Subject(s) - thylakoid , singlet oxygen , photochemistry , chemistry , membrane , cytochrome b6f complex , singlet state , indigenous , oxygen , biophysics , biology , biochemistry , physics , chloroplast , ecology , organic chemistry , excited state , atomic physics , gene
ABSTRACT Possible association of photodynamic sensitization by cytochrome b 6 / f complex (cyt b 6 / f ) via singlet oxygen ( 1 O 2 ) mechanism with photoinhibition damage to photosystem II (PS II) was studied using such subthylakoid preparations as photosystem I (PS I) particles, PS II core complex and cyt b 6 / f from spinach leaves. Upon exposure to bright light, PS II core complex lost photosynthetic electron transport activity to a certain extent, whose spectral dependence implied that pheophytin a is likely involved in photoinactivation of PS II core complex in itself. The presence of PS I particles exerted virtually no effect on PS II core photoinactivation. However, the inclusion of cyt b 6 / f in samples resulted in a marked exacerbation of the photoinactivation, particularly in UV‐A and blue light. Such effect of cyt b 6 / f was suppressed by azide and enhanced by the medium deuteration. Photogeneration of 1 O 2 from cyt b 6 / f was confirmed by ESR and spectrophotometry, chemically trapping 1 O 2 . Action spectra for both 1 O 2 photoproduction and PS II core photoinactivation by cyt b 6 / f bore a close resemblance to each other, seemingly carrying the absorption characteristics of the Rieske Fe‐S protein. A complex deficient in the Rieske protein prepared from intact cyt b 6 / f showed virtually no generation of 1 O 2 in light, whereas an efficient photoformation of 1 O 2 was seen in the Rieske protein preparation. The results suggest that cyt b 6 / f , rather specifically the Rieske center, may play a prominent role in photoinhibition processes through type II photosensitization in thylakoids.