A Mossbauer determination of the iron core particle size distribution in ferritin

The important biological iron bearing molecule ferritin has been studied using the 57Fe Mossbauer resonance. Natural and reconstituted ferritin samples have been studied in the temperature range 4--300 K. At low temperatures six-line magnetic hyperfine spectra are observed but with noticeably asymmetric line shapes, at high temperatures doublets are observed and in an intermediate temperature range (30--40 K) complex spectra characteristic of superparamagnetic behaviour are observed. From a theoretical study of the dependence of the hyperfine splitting parameters on particle size and from the experimental probability distributions obtained for these parameters from the Mossbauer spectra, it has been possible to derive the ferritin micelle particle size distributions for four different samples. It is found that the natural and reconstituted samples have roughly similar distributions except for the sample reconstituted from apoferritin in the presence of a phosphate environment. This sample is shown to have a slightly narrower particle size distribution centred on a smaller mean diameter. The information derived from these Mossbauer measurements are finally shown to be consistent with conclusions reached from separate biochemical experiments.