The kinetics and mechanism of oxidation of reduced spinach ferredoxin by molecular oxygen and its reduced products

Reduced spinach ferredoxin reacts with molecular oxygen in an autocatalytic reaction characterized by a hyperbolic dependence on oxygen concentration. The kinetics of the reaction indicate formation of a reduced ferredoxin-oxygen intermediate complex and production of superoxide anion which may also react with reduced ferredoxin. Hydrogen peroxide, which is formed from superoxide, in turn reoxidizes reduced ferredoxin at a rate nearly 10-times faster than that of the comparable reaction with oxygen. The kinetics of reaction of hydrogen peroxide with reduced ferredoxin are biphasic. The substrate dependence of the first phase of the reaction is consistent with a simple one-step equilibrium reaction. The second phase of the reaction could be eliminated by addition of the radical trapper, sodium formate.