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Photoinhibition affects the non‐heme iron center in photosystem II
Author(s) -
Gleiter Hermann M.,
Nugent Jonathan H.A.,
Haag Elisabeth,
Renger Gernot
Publication year - 1992
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(92)81188-r
Subject(s) - electron paramagnetic resonance , photoinhibition , electron transfer , photosystem ii , chemistry , photochemistry , electron acceptor , quantum yield , photosynthetic reaction centre , acceptor , electron transport chain , dcmu , photoinduced electron transfer , fluorescence , photosynthesis , nuclear magnetic resonance , biochemistry , physics , quantum mechanics , condensed matter physics
Effects on the PS II acceptor side caused by exposure to strong white light (180 W/m 2 ) of PS II membrane fragments (spinach) at pH 6.5 and 0°C were analyzed by measuring low temperature EPR signals and flash‐induced transient changes of the flourescence quantum yield. The following results were obtained: (a) the extent of the light induced g = 1.9 EPR signal as a measure of photochemical Fe 2+ Q − A formation declines with progressing photoinhibition. The half‐life of this effect is independent of the absence or presence of an exogenous electron acceptor during the photoinhibitory treatment; (b) in samples photoinhibited in the absence of an electron acceptor and subsequently incubated with K 3 [Fe(CN) 6 ] in the dark, the extent of the g = 8 EPR signal (reflecting the oxidized Fe 3+ form of the endogenous non‐heme iron center) and of the flash‐induced change of the flourescence yield (as a measure of fast electron transfer from Q − A to Fe 3+ after the first flash; [see (1992) Photosynth. Res. 31, 113–126] exhibits the same dependence on photoinhibition time as the g = 1.9 EPR signal; (c) in samples photoinhibited in the presence of an exogenous electron acceptor, the signals reflecting Fe 3+ ‐formation and fast electron transfer from Q − A to Fe 3+ decline faster than the g = 1.9 EPR signal. These results provide for the first time direct evidence that the endogenous non‐heme iron located between Q A and Q B is susceptible to modifications by light stress. The implications of this finding will be discussed.