Binuclear Manganese(III) Complexes as Electron Donors in D1/D 2/Cytochrome b 559 Preparations Isolated from Spinach Photosystem II Membrane Fragments

The capability of different manganese complexes to act as PS II electron donors in D 1/D2/ cytochrome b559 complexes has been analyzed by measuring actinic light-induced absorption changes at 680 nm (650 nm) and 340 nm, reflecting the photoaccumulation of Pheophytin - (Pheo-) and the reduction of NADP+, respectively. The data obtained reveal: a) the donor capacity of synthetic binuclear Mn(III)2 complexes containing aromatic ligands significantly exceeds that for MnCl2 in both cases, i.e. Pheo photoaccumulation and NADP+ reduction; b) manganese complexes can serve as suitable electron donors for light-induced NADP+ reduction catalyzed by D 1/D 2/cytochrome b 559 complexes and ferredoxin plus ferredoxin-NADP+ reductase under anaerobic conditions and c) the specific turnover rate of the system leading to NADP+ reduction is extremely, small. The implications of these findings are briefly, discussed.