Binuclear Manganese(III) Complexes as Electron Donors in D1/D2/Cytochrome b 559 Preparations Isolated from Spinach Photosystem II Membrane Fragments

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Abstract
The capability of different manganese complexes to act as PS II electron donors in D1/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 revealed: a) the donor capacity of synthetic binuclear Mn (III)₂complexes 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 D1/D2/cytochrome b559 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.

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