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

Abstract

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.

A comparison of the magnetic properties of polysaccharide iron complex (PIC) and ferritin

“…This may also apply for PIC with its higher density, but PIC also has a larger volume (average diameter = 70 A.) [10,17] than that for our horse spleen ferritin (average diameter = 62 A) [19]. In the superparamagnetic model of Neel [39], the distribution of blocking temperatures reflects the distribution of particle (core) vol umes, In our samples this still applies within the same assembly (same density) of particles.…”

“…PIC is synthesized on an industrial scale by Central Pharmaceuticals essentially by a patented procedure [18] which is described in detail elsewhere [1]. It has been suggested [1] that the synthetic PIC molecule resembles in some ways ferritin [19] as well as other iron-carbo hydrate complexes such as Imferon [20][21][22], which contain different forms and concentrations of iron oxyhydroxides. The differences among these iron oxyhydroxides are mainly due to long-range or der.…”

“…Both the PIC and ferritin samples are com prised of a distribution of particle sizes [10,19]. Experimentally, it is very difficult, but not impos sible, to prepare an assemblage of particles with a narrow size distribution, hence, each sample has a distribution of blocking temperatures.…”

“…As for Ferritin Type I (Fe3+), the particle size distribution has been determined for similar mammalian ferritin containing a range of Fe 3 + ions from 1730 to 2480 [19]. The average diameter was estimated to be 62 A, which gives a 3 volume of 1.3 X 10-19 cm • The anisotropy con stant for ferritin is assumed by many researchers [37] to be of the order K = 10 4 erg/cm 3 , which is that for FeOOH [38].…”

“…The average diameter was estimated to be 62 A, which gives a 3 volume of 1.3 X 10-19 cm • The anisotropy con stant for ferritin is assumed by many researchers [37] to be of the order K = 10 4 erg/cm 3 , which is that for FeOOH [38]. However, St. Pierre and others [8,9,19] showed that it should at least equal K = 10 5 erg/cm 3 , if not higher. Hence, using these values with the Hc(T = 0) for Ferritin Type I to get an order of magnitude for the magnetic moment of the ferritin molecule, we get '" 100 #LB' More information on the mag m FerI netic behavior of the Ferritin I sample is needed to obtain a more accurate value.…”