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 my 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 cmnperable 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.
A very broad circular dichroism band is observed in reduced spinach ferredoxin at 3600cm-1. The maximum At is +l.1 M-1. cm-1. The rotational strength is +1.0. 10-39erg.cm 3 (÷0.11 Debye-Bohr magneton); the minimum magnetic transition dipole moment is 0.14 Bohr magneton. These values are roughly consistent with expectations for a d ~ d transition of tetrahedrally coordinated Fe 2 +. No CD is detected in the oxidized protein between 5000 and 2800 cm-~.
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