Common metabolites and reducing/chelating agents do not mobilize iron from intracellular ferritin but can (like lysosomal extracts) dissolve ferritin iron mineral

Abstract

Although in several cell types release of storage Fe involves movement of ferritin (Ft) to and degradation in lysosomes (Lys), we wondered whether common Fe binding metabolites and reducing agents might also play a role, and also contribute to solubilization of the Fe mineral within Ft. HepG2 cells, loaded overnight with 59Fe so radioactivity was almost exclusively with Ft, were washed and incubated with and without mM concentrations of ascorbate, citrate and glutathione for 1–12h. Loss of 59Fe from cellular Ft was measured by rocket immunoelectrophoresis and phosphorimaging. No changes in Ft 59Fe contents were observed. The same was the case when cells were treated with agents that increased or reduced glutathione. To begin to understand how Lys juices might dissolve the Fe in Ft once the protein “shell” had been degraded, Fe mineral cores in Ft were purified after boiling to dissolve the protein. Portions of the cores were incubated with the same metabolites and reducing agents, at pH 5 or 7, and amounts of Fe in the supernatants were measured at various times thereafter. All 3 reagents efficiently solubilized Ft Fe, as did extracts from purified Lys. These findings support previous conclusions that Ft Fe is only released in conjunction with its degradation in Lys, and identifies substances that could be in Lys that would be able to dissolve the Fe exposed by degradation of the Ft shell. Supported in part by USPHS Grant HD 46949.