Role of critical charged residues in reduction potential modulation of ferredoxin-NADP+ reductase -: Differential stabilization of FAD redox forms

Reduction potential determinations of K75E, E139K and E301A ferredoxin-NADP(+) reductases provide valuable information concerning the factors that contribute to tune the flavin reduction potential. Thus, while E139 is not involved in such modulation, the K75 side-chain tunes the flavin potential by creating a defined environment that modulates the FAD conformation. Finally, the E301 side-chain influences not only the flavin reduction potential, but also the electron transfer mechanism, as suggested from the values determined for the E301A mutant, where E (ox/rd) and E (sq/rd) shifted +41 and +102 mV, respectively, with regard to wild-type. Reduction potentials allowed estimation of binding energies differences of the FAD cofactor upon reduction.