STUDY OF Fe K—EDGE ABSORPTION CHARACTERS AND RECONSTITUTION OF FERRITINS

The XANES of Fe K-edge in ferritins were measuured by using highly intensive synchrotron radiation light source and fluorescence technique. The Fe K-edge of ferrous sulfate and ferric nitrate solutions were characterized carefully. The differences of chemical shift are 1.3, 4.5 and 6.2 eV for the transition of 1s to 5t_1u, 7t_1u and uppermost states respectively. The fitting of Fe K-edge absorption curves in ferritins is based on the accurate determination of the Fe K-edges of FeSO₄ and Fe（NO₃）₃. The change of Fe valence state in ferritin was investigated quantitatively. The results show that the low Fe（Ⅱ） concentration and high ratio of Fe / protein decrease the oxidation velocity of ferritins during the reconstitution process. Zn binding on apoferritin can retard the oxidation of Fe（Ⅱ）. The results of dispersive XAS indicate that the natural ferritin is much more stable than the reconstituted one in the reduction. In the reconstitution process of ferritin, thepreedge structure of Fe K-edge seems to become clearer gradually, the environment around Fe atoms in ferritins varys from a normal oxygen octahydral coordinauon to an unsymmetry one. An obvious shoulder peak also appears on HSF carve just be hind the main peak. The results show that, with the extent of oxidation, the originally single shell coordinated Fe—O cluster is getting bigger and leads to the appearence of Fe-Fe multiple shell coordination, and then forms the Fe centers of ferritins.