A requirement for Ca2+ in the extraction of O2-evolving Photosystem 2 preparations from the cyanobacterium Anacystis nidulans

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Abstract
Ca2+ was essential for the retention of maximal O2-evolving activity in photosystem [PS] 2 particles extracted by using dodecyldimethylamine oxide from A. nidulans thylakoids. The effect cannot entirely be mimicked by using Mg2+. Ca2+ stimulates electron transport from diphenylcarbazide to 2,6-dichloroindophenol catalysed by lead-inhibited cation-free preparations, showing the presence of 2 cation-binding sites in these particles. PS 2 preparations extracted in Ca2+-containing buffer show the presence of 3 polypeptides at MW 30,000, 33,000 and 36,000, which are absent or much decreased in preparations extracted in Mg2+-containing buffer. The calmodulin antagonist chlorpromazine inhibits activity of the PS 2 preparation, suggesting the presence of a Ca2+-binding protein.