. "Contains chlorophyll a, beta-carotene, pheophytin, plastoquinone, a Mn(4)Ca cluster, heme and non-heme iron." . "Four successive photoreactions, resulting in a storage of four positive charges, are required to oxidize two water molecules to one oxygen molecule." . . . "Photosystem II" . "2 H(2)O + 2 plastoquinone + 4 light = O(2) + 2 plastoquinol." .