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Nanosecond fluorescence and absorbance changes in photosystem II at low redox potential
Author(s) -
Shuvalov V.A.,
Klimov V.V.,
Dolan E.,
Parson W.W.,
Ke B.
Publication year - 1980
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(80)80238-9
Subject(s) - photosynthesis , library science , chemistry , computer science , biochemistry
The electron-acceptor system in photosystem II (PS II) reaction centers of green plants is similar to that in bacterial reaction centers. In both kinds of reaction centers, a quinone (Q) acts as an early electron acceptor (ubiquinone or menaquinone in bacterial [l] and plastoquinone in PS II [2,3]). If the quinone is in the reduced form, continuous illumination causes the accumulation of a bacteriopheophytin (BPh) radical anion (BPh’-) in bacterial reaction centers [4-61 and of a pheophytin (Ph) radical anion (Ph.-) in PS II [7-l 31. The radical anions of BPh [5,14,15] and of Ph [12,13] participate inan exchange interaction with the radical anion of the quinone, coupled to a non-heme Fe atom, indicating that the distance between (B)Ph and Q is very short. The reduction of the quinone increases the formation of pigment triplet states in both bacteria [4,16] and PS II [29]. This is inhibited upon photoaccumulation of BPH’or Ph.-. Reduction of Q also is accompanied by the appearance of ns delayed fluorescence, which decreases during photoaccumulation of BPh’[4] or Ph.[9]. The delayed fluorescence has a characteristic magnetic field dependence in bacterial reaction centers [ 17-191 and in PS II [ 181 and an activation energy of 0.04-0.12 eV [4,9]. When the quinone in bacterial reaction centers is reduced, flash excitation generates a state ‘PF’, which has a lifetime of -10 ns [ 16,201. The transient state