Recovery Of Mrs3 Delta Mrs4 Delta Saccharomyces Cerevisiae Cells Under Iron- Sufficient Conditions And The Role Of Fe-580

Mrs3 and Mrs4 are mitochondrial inner membrane proteins that deliver an unidentified cytosolic iron species into the matrix for use in iron-sulfur cluster (ISC) and heme biosynthesis. The Mrs3/4 double-deletion strain (Delta Delta) grew slowly in iron-deficient glycerol/ethanol medium but recovered to wild-type (WT) rates in iron-sufficient medium. Delta Delta cells grown under both iron-deficient and iron-sufficient respiring conditions acquired large amounts of iron relative to WT cells, indicating iron homeostatic dysregulation regardless of nutrient iron status. Biophysical spectroscopy (including Mossbauer, electron paramagnetic resonance, and electronic absorption) and bioanalytical methods (liquid chromatography with online inductively coupled plasma mass spectrometry detection) were used to characterize these phenotypes. Anaerobically isolated mitochondria contained a labile iron pool composed of a nonheme high-spin Fe-II complex with primarily O and N donor ligands, called Fe-580. Fe-580 likely serves as feedstock for ISC and heme biosynthesis. Mitochondria from respiring Delta Delta cells grown under iron-deficient conditions were devoid of Few, ISCs, and hemes; most iron was present as Fe-III nanoparticles. O-2 likely penetrates the matrix of slow-growing poorly respiring iron-deficient Delta Delta cells and reacts with Fe-580 to form nanoparticles, thereby inhibiting ISC and heme biosynthesis. Mitochondria from iron-sufficient AA cells contained ISCs, hemes, and Fe-580 at concentrations comparable to those of WT mitochondria. The matrix of these mutant cells was probably sufficiently anaerobic to protect Fe-580 from degradation by O-2. An similar to 1100 Da manganese complex, an similar to 1200 Da zinc complex, and an similar to 5000 Da copper species were also present in Delta Delta and WT mitochondrial flow-through solutions. No lower-mass copper complex was evident.