MoFe proteins redox properties

The MoFe proteins exhibit complex redox properties. Each tetra-meric a2/32 molecule of MoFe protein contains two P clusters and two FeMoco centers and, as normally isolated in the presence of sodium dithionite, the FeMoco centers are EPR-active, exhibiting an S = spin state with g values near 4.3 and 3.7 and 2.01 (Fig. 6). The P clusters are EPR silent and there is a wealth of evidence (39) using a variety of techniques that indicates that the iron atoms in these clusters are all reduced to the Fe state. 

Pierik, A.J., Wassink, H., Haaker, H., and Hagen, W.R. 1993. Redox properties and EPR spectroscopy of the P clusters of Azotobacter vinelandii MoFe protein. European Journal of Biochemistry 212 51-61. 

The FeMo cofactor is located within the a subunit of the MoFe protein, 14 A away from the P cluster. It can be studied when it is buried within the MoFe protein or extracted into Ai-methylformamide (NMF). " " The FeMo cofactor can undergo reversible one-electron oxidation and reduction," and it is generally accepted that the FeMo cofactor provides the site for substrate reduction. The redox properties of the FeMo cofactor and their physiological relevance will be discussed further in Section 3.2. 

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