Hemerythrin diferrous forms

The two-electron reduction of the diferric forms of hemerythrin (51), ribonucleotide reductase (27, 50), and methane monooxygenase (31) yields dioxygen-sensitive diferrous forms of the proteins. All three can be generated by dithionite treatment of the corresponding diferric forms, although the RRB2 reduction requires methyl viologen as mediator. The Fe(II) oxidation state is more difficult to probe spectroscopically, and only recently have methods been developed that allow this state to be characterized further. 

The mechanisms for O, utilizaton by MMO d and RRB2jed are not established. The diferrous complex in either protein presumably serves to bind dioxygen, as in hemerythrin, forming a diferric peroxide complex (Fig. 19). This putative intermediate has been observed in neither the MMO nor the RRB2 cycle. Unlike in oxyHr, the peroxide intermediates of MMO and RRB2 must become activated to perform the required oxidation chemistry. This activation may derive from the ligand environments... 

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