Iron Content of Saccharomyces cerevisiae Cells Grown under Iron-Deficient and Iron-Overload Conditions

Fermenting cells were grown under Fe-deficient and Fe-overload conditions, and their Fe contents were examined using biophysical spectroscopies. The high-affinity Fe import pathway was active only in Fe-deficient cells. Such cells contained similar to 150 mu M Fe, distributed primarily into nonheme high-spin (NHHS) Fe-II species and mitochondrial Fe. Most NHHS Fe-II was not located in mitochondria, and its function is unknown. Mitochondria isolated from Fe-deficient cells contained [Fe4S4](2+) clusters, low- and high-spin hemes, S = 1/2 [Fe2S2](+) clusters, NHHS Fe-II species, and [Fe2S2](2+) clusters. The presence of [Fe2S2]2+ clusters was unprecedented; their presence in previous samples was obscured by the spectroscopic signature of Fe-III nanoparticles, which are absent in Fe-deficient cells. Whether Fe-deficient cells were grown under fermenting or respirofermenting conditions had no effect on Fe content; such cells prioritized their use of Fe to essential forms devoid of nanoparticles and vacuolar Fe. The majority of Mn ions in wild-type yeast cells was electron paramagnetic resonance-active Mn-II and not located in mitochondria or vacuoles. Fermenting cells grown on Fe-sufficient and Fe-overloaded medium contained 400-450 mu M Fe. In these cells, the concentration of nonmitochondrial NHHS Fe-II declined 3-fold, relative to that in Fe-deficient cells, whereas the concentration of vacuolar NHHS Fe-III increased to a limiting cellular concentration of similar to 300 mu M. Isolated mitochondria contained more NHHS Fe-II ions and substantial amounts of Fe-III nanoparticles. The Fe contents of cells grown with excessive Fe in the medium were similar over a 250-fold change in nutrient Fe levels. The ability to limit Fe import prevents cells from becoming overloaded with Fe.