THE FORMATION, STRUCTURE AND DISSOLUTION OF THE FERRITIN IRON CORE STUDIED BY X-RAY ABSORPTION SPECTROSCOPY

Ferritin is the solution to the problem of rust in biological material. Polynuclear iron complexes of up to 4500 Fe(III) atoms reversibly form a hydrous ferric oxide core inside a hollow spherical protein coat (apoferrritin) that permits the controlled release of iron as needed by the organism. To study intermediates in formation of the iron core (A) and factors which may alter core structure (B), we used EXAFS. To study the factors which may influence the kinetics of iron core reduction and dissolution (C), we used dispersive x-ray absorption spectroscopy (DXAS). The results show (A) that the protein coat appears to control initiation and nucleation of the iron core; (B) that model iron core structures can be influenced by sulfate which appears to nucleare domains of hematite (Fe2O3) that coexist in the soluble complex with FeO.OH ; and (C) that the reduction of core Fe is influenced by buffer ions, suggesting that the availability of ferritin iron in vivo may be modulated by cytoplasmic changes in small ions

X-Ray Absorption Fine Structure Spectroscopy in Fe Oxides and Oxyhydroxides

X-ray absorption fine structure (XAFS) spectroscopies [1–3] have advanced rapidly since the development of synchrotron radiation facilities that provide intense X-ray radiation with a continuous spectrum that can reach 120 keV. XAFS consists of measuring a signal proportional to the absorption coefficient, (E), as a function of the energy E of the incident X-ray radiation near and above the binding energy of a core level electron in an atom