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English: Fluorescence and EPR data representing the effects of HC removal on the electron-acceptor side of PSII. (A) Fluorescence measurements reflecting the decay of QA−, upon illumination of thylakoids of Synechocystis 6803 after the third flash (repetitive rate of 1 Hz) at pH 7.5 (modified and reproduced from Cao and Govindjee, 1988). The fluorescence decay was measured in control (i.e., HC-containing) samples (closed squares), HC-depleted samples (open triangles), and HC-depleted samples after the re-addition of 2.5 mM HCO3−. (B) EPR spectra of the iron–semiquinone in the dark-adapted PSII samples from thermophilic cyanobacterium P. laminosum upon 5 min illumination at 77 K in the absence (spectrum 1) and the presence of 100 mM formate (spectrum 2). The used concentration of formate (100 mM) has been shown to be sufficient for the removal all HC bound to PSII (Govindjee et al., 1991b; Shevela et al., 2008b). (C) EPR spectra of the g = 6 non-heme iron region of the dark-adapted PSII samples from spinach at pH 7.5. The spectra were obtained in the absence (spectrum 1) and the presence of 100 mM formate (spectrum 2). For EPR settings, see Nugent et al. (1988). Abbreviations: g, is the electronic splitting factor (in case of free electron g-factor, it has a value of 2.0023); mT (millitesla), values for the magnetic field. (B,C) were modified and reproduced from Nugent et al. (1988).