Iron Content of Saccharomyces cerevisiae cells grown under Iron-Deficient and Iron-Overload Conditions

摘要

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 ~150 μM Fe, distributed primarily into nonheme high-spin (NHHS) Fe^II species and mitochondrial Fe. Most NHHS Fe^II was not located in mitochondria, and their function is unknown. Mitochondria isolated from Fe-deficient cells contained [Fe4S4]²⁺ clusters, low- and high-spin hemes, S=½ [Fe2S2]¹⁺ 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 were 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 WT yeast cells was EPR-active Mn^II and not located in mitochondria or vacuoles. Fermenting cells grown on Fe-sufficient and Fe-overloaded medium contained 400 – 450 μM Fe. In these cells the concentration of nonmitochondrial NHHS Fe^II declined 3-fold, relative to in Fe-deficient cells, whereas the concentration of vacuolar NHHS Fe^III increased to a limiting cellular concentration of ~ 300 μM. 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 of nutrient Fe levels. The ability to limit Fe import prevents cells from overloading with Fe.