Iron Content of Saccharomyces cerevisiae Cells Grown under Iron-Deficient and Iron-Overload Conditions
journal contributionposted on 08.01.2013, 00:00 by Gregory P. Holmes-Hampton, Nema D. Jhurry, Sean P. McCormick, Paul A. Lindahl
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) FeII species and mitochondrial Fe. Most NHHS FeII 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 FeII 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 FeIII 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 MnII 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 FeII declined 3-fold, relative to that in Fe-deficient cells, whereas the concentration of vacuolar NHHS FeIII increased to a limiting cellular concentration of ∼300 μM. Isolated mitochondria contained more NHHS FeII ions and substantial amounts of FeIII 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.