title: The 28 kDa apoprotein of CP 26 in PS II binds copper.
abstract: Photosystem II (PS II) particles isolated from spinach in the presence of 10 μM CuSO4 contained 1.2 copper/300 Chl that was resistant to EDTA. When CuSO4 was not added during the isolation, PS II particles contained variable amounts of copper resistant to EDTA (0.1-1.1 copper/300 Chl). No correlation was found between copper content and oxygen evolving capacity of the PS II particles. To identify the copper binding protein, we developed a fractionation procedure which included solubilisation of PS II particles followed by precipitation with polyethylene glycol. A 22-fold purification of copper with respect to protein was achieved for a 28 kDa protein. Partial amino acid sequence of a 13 kDa fragment, obtained after V8 (endo Glu-C) protease treatment, showed identity with CP 26 over a 14 amino acid stretch. EPR measurements on the purified protein suggest oxygen and/or nitrogen as ligands for copper but tend to exclude sulfur. We conclude that the 28 kDa apoprotein of CP 26 from spinach binds one copper per molecule of CP 26. A possible function for this copper protein in the xanthophyll cycle is discussed.
authors: Plant Biochemistry, University of Lund, POB 7007, S-220 07, Lund, Sweden.
authors: P O
authors: PO
authors: Arvidsson
authors: C E
authors: CE
authors: Bratt
authors: L E
authors: LE
authors: Andréasson
authors: H E
authors: HE
authors: Kerlund