BINUCLEAR MANGANESE(III) COMPLEXES AS ELECTRON-DONORS IN D1 D2/CYTOCHROME B559 PREPARATIONS ISOLATED FROM SPINACH PHOTOSYSTEM-II MEMBRANE-FRAGMENTS/

The capability of different manganese complexes to act as PS II electr on donors in D1/D2/cytochrome b559 complexes has been analyzed by meas uring actinic light-induced absorption changes at 680 nm (650 nm) and 340 nm, reflecting the photoaccumulation of Pheophytin(-) (Pheo(-)) an d the reduction of NADP(+), respectively. The data obtained reveal: a) the donor capacity of synthetic binuclear Mn(III)(2) complexes contai ning aromatic ligands significantly exceeds that for MnCl2 in both cas es, i.e. Pheo(-) photoaccumulation and NADP(+) reduction; b) manganese complexes can serve as suitable electron donors for light-induced NAD P(+) reduction catalyzed by D1/D2/cytochrome b559 complexes and ferred oxin plus ferredoxin-NADP(+) reductase under anaerobic conditions and c) the specific turnover rate of the system leading to NADP(+) reducti on is extremely small. The implications of these findings are briefly discussed.