Iron-binding and mobilization from ferritin by polypyridyl ligands

Abstract

Polypyridyl ligands were investigated for their ability to bind and mobilize iron(II) from ferritin in aqueous solution. Association constants with iron(II) (pFe^II) were determined for the pentadentate ligands N4Py (pFe^II = 14.4) and Bn-TPEN (pFe^II = 13.7) using a competition method with the hexadentate ligand TPEN (pFe^II = 14.6, 0.1 M KNO₃). Ferrous complexes were formed using the polypyridyl ligands and ferritin as the sole iron source in the presence of reductant. The observed rates of iron mobilization from ferritin were dependent on reductant and were higher in the presence of ascorbate than dithiothreitol. TPEN, N4Py and Bn-TPEN demonstrated comparable and in some cases faster rates and higher levels of iron mobilization when compared to the iron(II) chelator 1,10-phenanthroline, particularly at low concentrations of chelator.