A short Fe-Fe distance in peroxodiferric ferritin: Control of Fe substrateversus cofactor decay?

The reaction of oxygen with protein diiron sites is important in bioorganic syntheses and biomineralization. An unusually short Fe-Fe distance of 2.53 angstroms was found in the diiron (mu-1,2 peroxodiferric) intermediate tha t forms in the early steps of ferritin biomineralization. This distance sug gests the presence of a unique triply bridged structure. The Fe-Fe distance s in the mu-1,2 peroxodiferric complexes that were characterized previously are much longer (3.1 to 4.0 angstroms). The 2.53 angstrom Fe-Fe distance r equires a small Fe-O-O angle (similar to 106 degrees to 107 degrees). This geometry should favor decay of the peroxodiferric complex by the release of H2O2 and mu-oxo or mu-hydroxo diferric biomineral precursors rather than b y oxidation of the organic substrate. Geometrical differences may thus expl ain how diiron sites can function either as a substrate (in ferritin biomin eralization) or as a cofactor (in O-2 activation).