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The MoFe protein from Azotobacter vinelandii undergoes a six-electron oxidation by various organic dye oxidants with full retention of initial activity. Reduction of the oxidized protein by S2O42- and by controlled potential electrolysis indicates the presence of two reduction regions at -290 and -480 mV, each requiring three electrons for complete reaction. Control of the oxidation conditions provides a means for preparing two distinct MoFe protein species selectively oxidized by three electrons. Selective reduction of the redox region at -290 mV causes development of the EPR signal associated with fully reduced MoFe protein while reduction at -480 mV produces a change in the visible spectrum but has no effect on the EPR signal intensity. Kinetic differences for reduction of the two redox regions indicate that the cofactor region undergoes a more rapid reaction with reductant than the other metal redox sites.

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