A study of ferritin iron formation in the rabbit alveolar macrophage

In order to investigate the intracellular pathway of iron to ferritin, rabbit alveolar macrophages were incubated with ⁵⁹FCl₃, homogenized by sonification, and a soluble cell fraction separated from the stroma by centrifugation at 23 000 g. The soluble fraction was examined by gel filtration using Sephadex. Two peaks were identified in the eluate at 254 nm; peak I contained a group of proteins, including ferritin, and most of the eluted radioactivity. The ⁵⁹Fe in this peak was confined to ferritin; no other ⁵⁹Fe-binding protein was identified. Peak II contained a small amount of ⁵⁹Fe. Chase experiments with ‘cold’ iron showed that peak I ⁵⁹Fe was derived from ⁵⁹Fe associated with the cell stroma. A protein carrier for ⁵⁹Fe between the stroma and ferritin was not identified in the eluate of the soluble fraction. Rather it appeared that iron moved from the stroma through the cytoplasm to ferritin in a low molecular weight form.