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The effect of chloride on paramagnetic coupling of manganese in the oxygen-evolving complex of CaCl2--washed PS II preparations was examined using Q-band ESR. When these PS II preparations were depleted of chloride, a strong 6-line ESR signal characteristic of protein-bound, uncoupled manganese was observed. Incubation at high chloride concentrations caused the disappearance of this signal. By repeated removal and addition of chloride, the signal could be cycled on and off without loss of bound manganese. When in a chloride-depleted state, the ESR-detectable protein-bound manganese could be removed by treatment with EDTA. Subsequent heating of EDTA-treated preparations revealed a second pool of protein-bound manganese associated with PS II. One of these pools requires a high concentration of chloride to maintain paramagnetic coupling while the second pool (within the limits of our observations) does not appear to require chloride for the maintenance of the paramagnetically coupled state. © 1986.

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FEBS Letters

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