Spectroscopic Characterization of Ferritins and Bacterioferritins

In combination with the rapid freeze-quench methodology, EPR spectroscopy has been instrumental in the detection of reaction intermediates during the reconstitution of horse spleen ferritin from apoferritin, Fe , and O2 [486]. Within the first second after mixing of the reactants, a monomeric Fe -protein complex with a characteristic resonance at geff = 4.3, a mixed-valent Fe -Fe species with a peak 1-87 (which accumulates quantitatively from the monomeric Fe species), and a radical species (gy = 2.042, = 2.0033) that may be associated with either 

Fe or Fe (whose function may potentially involve storage of the oxidizing equivalents for subsequent Fe oxidation) have been observed. 

Similarly, the oxidation of Fe during iron core formation in recombinant human H subunit ferritin and its variants has been investigated by stopped-ftow kinetics and Mossbauer spectroscopy [494]. An intermediate species, attributed to the purple Fe -Tyr34 complex in the Fe2 site, was shown to form rapidly ( ox 1000 s ) and to decay within the first 5-10 s. This Fe -tyrosinate complex was shown to form following the rapid uptake and oxidation of Fe, and was proposed as one of the initial steps in the fast mineralization process [474]. The oxidation of Fe has been shown to lead to the formation of various species, including Fe monomers, dimers, and some larger clusters. Specifically, the observed fast oxida- 

NATASA MITIC, GERHARD SCHENK AND GRAEME R. HANSON 

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