STRUCTURE OF THE IRON-CONTAINING CORE IN FERRITIN BY THE EXTENDED X-RAY ABSORPTION FINE-STRUCTURE TECHNIQUE

Extended X-ray absorption fine structure (EXAFS) measurements are used to determine the structure of the ironcontaining core of ferritin. By comparing the EXAFS from ferritin with that from an Fe-glycine model compound, it is found that at room temperature the irons are surrounded by 6.4 ± 0.6 oxygens at 1.95 ± 0.02 Å which are likely in a distorted octahedral arrangement. Each iron also has 7 ± 1 iron neighbors at an average distance of 3.29 ± 0.05 Å. Considerable structural disorder was found which increased when the ferritin solution was frozen, indicating a possible phase transition occurring at lower temperatures. Combining these results with the known stoichiometry and density it is shown that the structure for the iron core is a layered arrangement with the iron in the interstices between two nearly close-packed layers of oxygens with approximate sixfold rotational symmetry, and that these compact O-Fe-O layers are only weakly bound to adjacent layers. The known phosphorus component is accounted for by terminating the layer into a strip whose width naturally explains the size of the core. The ferritin core consists, in this picture, of a strip folded back and forth upon itself in the form of a pleat. Measurements are also presented for two forms of the polymer of Spiro and Saltman. and it is found that only one form is possibly similar to ferritin. © 1979, American Chemical Society. All rights reserved.