IRON K-EDGE ABSORPTION SPECTROSCOPIC INVESTIGATIONS OF THE CORES OF FERRITIN AND HAEMOSIDERINS

The extended X-ray absorption fine structure (EXAFS) associated with the iron K-edge has been measured and interpreted for ferritin and haemosiderin extracted from horse spleen, and haemosiderin extracted from the livers of humans with treated primary haemochromatosis, and from the spleens of humans with treated secondary haemochromatosis. For ferritin, the data are consistent with, on average, each iron atom being in an environment comprised of approx. six oxygen atoms at 1.93 +/- 0.02 angstrom, approx. 1.5 iron atoms at 2.95 +/- 0.02 angstrom and approx. 1.1 iron atoms at 3.39 +/- 0.02 angstrom, with a further shell of oxygens at approx. 3.6 angstrom. Iron in horse spleen haemosiderin is in an essentially identical local environment to that in horse spleen ferritin. In contrast, the EXAFS data for primary haemochromatosis haemosiderin indicate that the iron-oxide core is amorphous; only a single shell of approx. six oxygen atoms at approx. 1.94 +/- 0.02 angstrom being apparent. Secondary haemochromatosis haemosiderin shows an ordered structure with approx. 1.4 iron atoms at both 2.97 +/- 0.02 and 3.34 +/- 0.02 angstrom. This arrangement of iron atoms is similar to that in horse spleen haemosiderin, but the first oxygen shell is split with approx. 2.9 atoms at 1.90 +/- 0.02 angstrom and approx. 2.7 at 2.03 +/- 0.02 angstrom, indicative of substantial structural differences between secondary haemochromatosis haemosiderin and horse spleen haemosiderin.