Oxidation-reduction and transient kinetic studies of spinach ferredoxin-dependent glutamate synthase.

Spinach leaf ferredoxin-dependent glutamate synthase has been shown to contain one FMN but no FAD. The oxidation-reduction midpoint potentials of the FMN and the other prosthetic group, a [3Fe-4S]1+,0 cluster, have both been estimated to be -225 mV by cyclic voltammetry. Confirmation of the isopotential nature of the two prosthetic groups of the enzyme has been obtained using deazariboflavin phototitrations. Flash photolysis measurements have allowed determination of the second-order rate constants for reduction of both of the prosthetic groups of the enzyme by the 5-deazariboflavin semiquinone radical.