Iron core formation in horse spleen ferritin: Magnetic susceptibility, pH, and compositional studies

Abstract

Horse spleen ferritin (HoSF) reconstituted with small iron cores ranging in size from 8 to 500 iron atoms was studied by magnetic susceptibility and pH measurements to determine when the added Fe 3 + begins to aggregate and form antiferromagnetically coupled clusters and also to determine the hydrolytic state of the iron at low iron loading. The Evans NMR magnetic susceptibility measurements showed that at iron loadings as low as 8 Fe 3 +/HoSF, at least half of the added iron atoms were involved in antiferromagnetic exchange interactions and the other half were present as isolated iron atoms with S = 5/2. As the core size increased to about 24 iron atoms, the antiferromagnetic exchange interactions among the iron atoms increased until reaching the limiting value of 3.8 Bohr magnetons per iron atom, the value present in holo HoSE HoSF containing eight or more Fe3+ to which eight Fe z + were added showed that the Fe z + ions were at sites remote from the Fe 3 4; and that the resulting HoSF consisted of individual, noninteracting Fe z + and the partially aggregated Fe 3 +. pH measurements for core reduction showed that Fe(OH)3 was initially present at all iron loadings but that in the absence of iron chelators the reduced iron core is partially hydrolyzed. Proton induced x-ray emission spectroscopy showed that Cl-is transported into the iron core during reduction, forming a stable chlorohydroxy Fe(II) mineral phase.Ferritin from animal sources is a multisubunit protein with an internal cavity that sequesters a core of iron atoms as the ferric oxy-hydroxide mineral ferrihydrite, nominally 5Fe z 0 3 • 9H z O, associated with variable amounts of

Molecular diffusion into horse spleen ferritin: a nitroxide radical spin probe study

“…The failure of the negatively charged 4-carboxy-TEMPO radical to penetrate the protein does not preclude smaller anions such as Cl-, OH-, and HPO2from gaining access to the ferritin cavity, however. Experimental results show that chloride is transported into the cavity during the chemical reduction of the iron core by methylviologen (Hilty et al, 1994). In the special case of OH-, H+ ion is generated in the interior of the ferritin during Fe(III) hydrolysis to form FeOOH with charge compensation being achieved by the H+ ion diffusion out of the cavity (Chen- Barrett, 1994).…”

Quantitative susceptibility mapping (QSM) of white matter multiple sclerosis lesions: Interpreting positive susceptibility and the presence of iron

“…In the MS lesions, in vitro experiments show mostly ferritin in microglia . Therefore, [Fe] maps were converted to susceptibility with an estimate of the molar susceptibility of iron at room temperature like ferritin; 3.78 effective Bohr magnetons and a brain tissue density of 1.04 g/cm 3 . Using the Langevin equation, iron contributes, =1.4ppb*[Fe], where [Fe] is in mg/kg.…”

Mineralization in Ferritin: An Efficient Means of Iron Storage

“…Ferritin cores containing iron in the ferrous state can be produced either by incomplete oxidation of Fe(II) that has been added to the apoprotein or by electrochemical reduction of the Fe(III) core of the holoprotein (Hilty et al, 1994;Rohrer et al, 1987;Watt et al, 1985). Whether such cores occur in vivo or play some role in the biochemistry of iron is unknown.…”