The ferritin superfamily of iron storage proteins includes ferritin proper and Dps (DNA binding protein from starved cells) along with bacterioferritin. We examined the release of Fe from the Dps of Trichodesmium erythraeum (Dpstery) and compared it to the release of Fe from horse spleen ferritin (HoSF) under various conditions. Both desferrioxamine B (DFB), a Fe(III) chelator, and ascorbic acid were able to mobilize Fe from Dpstery at rates comparable to those observed for HoSF. The initial Fe release rate from both proteins increased linearly with the concentration of DFB, suggesting that the chelator binds to Fe in the protein. A small but significant rate obtained by extrapolation to zero concentration of DFB implies that Dpstery and HoSF might release Fe(III) spontaneously. A similar result was observed for HoSF in the presence of sulfoxine. In a different experiment, Fe(III) was transferred from holoferritin to apotransferrin across a dialysis membrane in the absence of chelator or reducing agent. The apparent spontaneous release of Fe from HoSF and Dpstery brings forth the hypothesis that the Fe core in Fe storage proteins might be continuously dissolving and re-precipitating in vivo, thus maintaining it in a highly reactive and bioavailable form.
Bibliographical noteFunding Information:
This work was supported by the Center for Environmental BioInorganic Chemistry, NSF Grant # CHE-0221978.
- Iron dissolution
- Iron storage proteins