Is there a direct chloride cofactor requirement in the oxygen-evolving reactions of photosystem II?

Tom Wydrzynski, Frank Baumgart, Fraser MacMillan, Gernot Renger

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Abstract

The dark incubation at room temperature of photosystem II (PS II) membrane fragments in a chloride-free medium at pH 6.3 slowly leads to large chloride-restorable and non-restorable O evolution activity losses with time as compared with control samples incubated in the presence of 10 mM NaCl. The chloride requirement in O evolution generated under these conditions reveals a complex interplay among various experimental parameters, including the source of the plant material, the times of incubation, the sample concentration, the chloride concentration, as well as those treatments which are believed to specifically displace chloride from PS II such as alkaline pH pretreatment and NaSO addition. The results indicate that secondary, structural changes within the PS II complex are an important factor in determining the influence of chloride on the O evolution activity and raise the question whether or not chloride ions actually play a direct cofactor role in the water-oxidizing reactions leading to O evolution.
Original languageEnglish
Pages (from-to)59-72
Number of pages14
JournalPhotosynthesis Research
Volume25
Issue number1
DOIs
Publication statusPublished - 1 Jul 1990

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