Cores of Ferritins and Bacterioferritins

Other physical properties also show that the iron cores of native ferritins and bacterioferritins are different. Mossbauer spectra of ferritins measured as a function of temperature (Fig. 1) show quadrupole split doublets, with an isomer shift typical of Fe +, gradually being replaced as the temperature is lowered (between about 50 and 15 K) by a magnetic hyperfine spectrum (30, 31). The transition temperature, Tb, is lower than the ordering temperature, Tord (240 K) observed for bulk ferrihydrite (32), because of fluctuations in the direction of mag- 

Fe Mossbauer absorption spectra measured for horse spleen ferritin measured at four temperatures relative to a room-temperature CoRh source. Reproduced from Ref 31. The solid lines represent computer fits to the experimental data. The average blocking temperature, Tb, for this ferritin is near 40 K and the calculated distribution of iron core diameters extends from 36 to nearly 90 A. with a maximum at 63 A. 

Chemical Composition of Horse Spleen Ferritin Iron Cores  

Ferritin source Fe atoms/ molecule Fe atoms/ phosphate Fe atoms/ P atoms Crystallinity n 7 ord Ref  

The presence on apoferritin of ferroxidase centers is suggested by four observations (1) that tbe initial oxidation step when Fe(II) is added to apoferritin requires a specific oxidant, dioxygen (48Y, (2) that Fe(III) can be produced from Fe(II) in the presence of apoferritin—and intercepted by transferrin under conditions in wbicb hydrolysis is kept 

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