A redox-dependent interaction between two electron-transfer partners involved in photosynthesis

Ferredoxin:NADP(+):reductase (FNR) catalyzes one terminal step of the conve rsion of light energy into chemical energy during photosynthesis. FNR uses two high energy electrons photoproduced by photosystem I (PSI) and conveyed , one by one, by a ferredoxin (Fd), to reduce NADP+ to NADPH. The reducing power of NADPH is finally involved in carbon assimilation. The interaction between oxidized FNR and Fd was studied by crystallography at 2.4 Angstrom resolution leading to a three-dimensional picture of an Fd-FNR biologically relevant complex. This complex suggests that FNR and Fd specifically inter act prior to each electron transfer and disassemble upon a redox-linked con formational change of the Fd.