Utilization of iron complexes in an animal cell

The ciliate protozoan Tetrahymena thermophila was grown in synthetic nutrient medium in the absence of the iron chelator citrate. Utilization and toxicity of various iron compounds or complexes in iron‐starved cells were assessed from the number of cell doublings obtained within a standard time. The compounds tested included complexes formed between ortho‐phosphates and two forms of ferric hydroxides, native and cationized ferritin, and tris‐acetylacetonato Fe(III). The ferric hydroxo ortho‐phosphate particles are toxic and can be removed from the medium by Millipore filtration. Uptake of ferritin and tris‐acetylacetonato‐Fe(III) is independent of food vacuole formation and seems to occur by micropinocytosis and by plasma membrane translocation, respectively.