Structure-function relationships in the ferredoxin/ferredoxin: NADP+ reductase system from Anabaena.

We have used a combination of laser flash photolysis time-resolved spectrophotometry and site-specific mutagenesis of surface amino acid residues to investigate the structural factors which influence electron transfer from Anabaena ferredoxin to its physiological partner ferredoxin-NADP+ reductase. Two ferredoxin residues (E94 and F65) are found to be highly critical interaction sites, whereas other nearby residues are found to be either inconsequential or to have only moderate effects. Basic residues near the N-terminus of the reductase are also found to exert a significant influence on interprotein electron transfer. The mechanistic implications of these results are discussed.