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Electron acceptors of photosystem 2 in the cyanobacterium Phormidium laminosum
Author(s) -
Atkinson Y.E.,
Evans M.C.W.
Publication year - 1983
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(83)80433-5
Subject(s) - photosystem ii , p680 , electron acceptor , dcmu , chemistry , electron paramagnetic resonance , semiquinone , acceptor , photochemistry , pheophytin , p700 , photosynthetic reaction centre , flavodoxin , redox , photosystem i , electron transfer , photosynthesis , nuclear magnetic resonance , inorganic chemistry , physics , ferredoxin , biochemistry , enzyme , condensed matter physics
Photosystem 2 preparations with very high rates of oxygen evolution from the thermophilic cyanobacterium Phormidium laminosum have been studied by EPR spectrometry. In the presence of DCMU the g = 1.82 signal of the iron—quinone electron acceptor (Q) can be observed. It is proposed that DCMU is necessary to disrupt a magnetic interaction, between the semiquinone forms of Q and the secondary acceptor B, which otherwise prevents detection of the Q − Fe signal. A doublet EPR signal arising from magnetic interaction between Q − Fe and the reduced intermediary electron acceptor pheophytin (I − ), and a spin‐polarized triplet signal assumed to arise from the back reaction between I − and P680 + can also be seen. Preliminary redox titrations of Q reduction have been carried out, indicating E m ⋍ 0 mV.