Involvement of oxo-bridged binuclear iron centers in oxygen transport, oxygen reduction, and oxygenation.

The occurrence of an oxo-bridged binuclear iron site is well-established for the oxygen transport protein, hemerythrin, and strongly implicated in ribonucleotide reductase, purple acid phosphatase, ferritin, and methane monooxygenase. Key identifying characteristics are an antiferromagnetic interaction between the two iron atoms, an Fe-O-Fe vibrational mode in the resonance Raman spectrum, and an S = 1/2 EPR signal upon one-electron reduction. In hemerythrin the oxo bridge serves as a hydrogen bond acceptor which stabilizes the bound hydroperoxide. In ribonucleotide reductase both the binuclear iron center and a protein tyrosine undergo oxidation in the presence of molecular oxygen, whereas in methane monooxygenase a binuclear iron moiety may activate O2 for substrate oxygenation.